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Three Elements

Article reprinted with permission and originally appeared in the February Issue of the NYMC Bulletin - http://www.newyorkmineralogicalclub.org/

 “It’s Elemental” is a series of columns by Bill Shelton written this in year in recognition of the United Nations’ International Year of the Periodic Table of Chemical Elements.

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 We all know oxygen, silicon, and aluminum are common elements in the Earth’s crust. They are also the three most common but in terms of the number of minerals that contain them, we find a somewhat different accounting. Oxygen is the most numerous in the number of species, silicon is third and aluminum is seventh. They all have more than 1,000 known species which is also the case for five other elements. (Those other elements are hydrogen, calcium, iron, sulfur and sodium.)

These elements can occur in an uncombined state. Oxygen is present as an important component of our atmosphere (about 21%). We cannot consider it as a mineral however, because it is a gas; minerals are defined as solids. Silicon has a presence in the Earth’s crust as a native element just as we find in the list of Back, 2018. One unusual place where we see this is in fulgarites that form when lightning strikes the earth’s surface. Aluminum, perhaps surprising us, occurs in two elemental forms – one we call aluminum while the other is called steinhardtite. (Dr. Paul Steinhardt lectured to the NYMC in January 2014 about quasicrystals.) I would readily consider the native elements for silicon and aluminum as greatly restricted in occurrence; specimens are mainly very small and probably of little interest to many mineral collectors.

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The combined occurrences for these three elements are very well known. Oxygen and silicon alone produce quartz, opal and a host of varietals like agate and jasper. The essential materials for all of these species are the same. Their widespread presence, and interest to collectors, makes them important to us. Far less interest is noted for tridymite and coesite who also share identical chemistry. If one or two other elements are included, there are many more possible species.

Oxygen and aluminum produce the species corundum which includes the varieties ruby and sapphire. It is very important as a gem material and will be likely to be present in a huge number of mineral and/or gem collections. Diaspore comes close but requires hydrogen with the other elements listed here. Adding another element or two greatly expands the number of possible species as we see with diaspore.

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For all three together, we find the mineral kyanite. This is very popular amongst collectors especially as bright blue crystalline examples. The occasional gem usage appears to be quite limited but the very best faceted stones are quite appealing. Sillimanite and andalusite belong here but seem to be less common in some collections. All three species can be used to suggest the degree of metamorphism in rocks.

If we add one or two more elements, we have the bulk of the rock-forming minerals. Feldspars, micas, pyroxenes, amphiboles and so forth are composed mainly of oxygen, silicon, aluminum and one or two more elements. We see, therefore, that despite the very common presence of these elements in mineral species, there are really very few examples made up of only these three elements. Perhaps this is not what you would have guessed. When you look at lists for say, aluminum species, you find the various combinations noted in nature exceeds 1,000.


2019 International Year of the Periodic Table

The UN Proclaims 2019 the International Year of the Periodic Table of Chemical Elements

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 On 20 December 2017, during its 74th Plenary Meeting, the United Nations (UN) General Assembly 72nd Session has proclaimed 2019 as the International Year of the Periodic Table of Chemical Elements (IYPT 2019). In proclaiming an International Year focusing on the Periodic Table of Chemical Elements and its applications, the United Nations has recognized the importance of raising global awareness of how chemistry promotes sustainable development and provides solutions to global challenges in energy, education, agriculture and health. Indeed, the resolution was adopted as part of a more general Agenda item on Science and technology for development. This International Year will bring together many different stakeholders including UNESCO, scientific societies and unions, educational and research institutions, technology platforms, non-profit organizations and private sector partners to promote and celebrate the significance of the Periodic Table of Elements and its applications to society during 2019.

The development of the Periodic Table of the Elements is one of the most significant achievements in science and a uniting scientific concept, with broad implications in Astronomy, Chemistry, Physics, Biology and other natural sciences. The International Year of the Periodic Table of Chemical Elements in 2019 will coincide with the 150th anniversary of the discovery of the Periodic System by Dmitry Mendeleev in 1869. It is a unique tool enabling scientists to predict the appearance and properties of matter on Earth and in the Universe. Many chemical elements are crucial to enhance the value and performance of products necessary for humankind, our planet, and industrial endeavors. The four most recent elements (113, 115, 117 and 118) were fully added into the Periodic Table, with the approval of their names and symbols, on 28 November 2016.

The International Year of the Periodic Table of the Chemical Elements will coincide with the Centenary of IUPAC (IUPAC100). The events of IUPAC100 and of IYPT will enhance the understanding and appreciation of the Periodic Table and chemistry in general among the public. The 100th Anniversary of IUPAC will be on the UNESCO Calendar of Anniversaries on 28th July 2019.

“As the global organization that provides objective scientific expertise and develops the essential tools for the application and communication of chemical knowledge for the benefit of humankind, the International Union of Pure and Applied Chemistry is pleased and honored to make this announcement concerning the International Year of the Periodic Table of Chemical Elements” said IUPAC President, Professor Natalia Tarasova.

 Chemical elements play a vital role in our daily lives and are crucial for humankind and our planet, and for industry. The International Year of the Periodic Table of Chemical Elements will give an opportunity to show how they are central to linking cultural, economic and political aspects of the global society through a common language, whilst also celebrating the genesis and development of the periodic table over the last 150 years. It is critical that the brightest young minds continue to be attracted to chemistry and physics in order to ensure the next generation of scientists, engineers, and innovators in this field. Particular areas where the Periodic Table and its understanding have had a revolutionary impact are in nuclear medicine, the study of chemical elements and compounds in space and the prediction of novel materials.


 The IYPT is endorsed by a number of international Scientific Unions and the International Council for Science (ICSU). The IYPT will be administered by an International Steering Committee in collaboration with the UNESCO International Basic Sciences Programme and an International Secretariat, to start operating in early 2018. In addition to IUPAC, IYPT is supported by the International Union of Pure and Applied Physics (IUPAP), the European Chemical Sciences (EuCheMS), the International Astronomical Union (IAU) and the International Union of History and Philosophy of Science and Technology (IUHPST).

Cubic Crystals

By Bill Shelton


It seems as though it might be a simple matter to deal with this topic.  Well, perhaps it is but I have the idea that mineral collectors may not exactly know what is involved.  Any source reveals that there are seven systems and 32 crystal classes where the system is subdivided based on characteristic symmetry for that system.  Here, we shall look at the cubic system and the five classes within the system.  Each class is named for a certain form that characterizes the class; also, we find a customary reference to the class where numbers and letters will also describe the same class.  This is also called the point group.   The full symbol and an abbreviated symbol are commonly used for the same purpose.  Below, I have arbitrarily listed examples that I consider to be more or less important for collectors.  Species that are not included are the ones I think many collectors do not seem interested in as well as rarely found samples that will be hard to collect and/or purchase.

The first class is the tetrahedral pentagonal dodecahedral; also noted as 23.  We find the name tetartohedral used as well.  References may call this class the ullmannite type.  Some older sources say cobaltite belongs here.  Actually, it has been moved to the orthorhombic, pseudcubic division where we can see crystals that look like pyritohedra but are not. Kostov and Kostov (1999) indicate that it can and does resemble pyrite which is in a higher symmetry class, 2m3.  Sadly, this is the most notable member of this class.  So, who’s left?  Well, we have ullmannite and I believe it is of little interest so this class is of minor concern in my opinion for we collectors.  Ullmannite fits in P23 space group and will display octahedral, pyritohedral and tetrahedral crystal forms as well as twins.

 The next class (2m3 or m3) is the di(akis) dodecahedral which is also labeled pentagonal hemihedral, dipliodal, didodecahedral and pyritohedral class.  References may call it the pyrite type.  I choose to refer to four species as the prime examples for us to consider.  This class is important and the members are likely to be familiar and present in your collections.  Sperrylite, Pa3 space group, resembles pyrite especially regarding morphology and variation of crystal habits.  It is less common among collector material than the others listed here.  Smaltite, a name found in older sources has been discredited and is considered as a variety of skutterudite.  The Handbook of Mineralogy (1990) shows analytical data for CoAs2 (more like the material previously classified as smaltite and data for CoAs3 that is akin to the original skutterudite.  Space group Im3 is for this mineral; cubic, octahedral and cubo-octahedral forms are commonly present.  Bixbyite, Im3 space group, exhibits cubic forms and often has twins.  Pyrite, the namesake here, is a member of Pa3 space group.  Pyritohedral, dodecahedral, cubic, and octahedral forms are common as are twins.  It is the most prevalent example for this class.

 Third among the five classes, we find bar43m.  This is the hexa(kis) tetrahedral, hextetrahedral, of tetrahedral hemihedral class. The names tetrahedral class and tetrahedrite type are also used in some sources.  Members more or less noted in collections and numerous by comparison to some other classes, include sphalerite.  It is Fbar43m space group and an exhibit tetrahedral, cubo-octahedral, dodecahedral forms and twins.  This very common mineral is no doubt well-known to you.  Tetrahedrite, Ibar43m space group, shows tetrahedral forms and twins.  Tennantite, also Ibar43m space group, looks essentially the same in general as tetrahedrite.  Last, we find helvite, space group Pbar43m, with tetrahedral forms and twins. 

 Class 432 also noted as 43 is the plagiohedral.  I have chosen to say no more - it has no mineral representatives anyway.  Previously, cuprite was placed here.  The Handbook says it is m3m and space group Pn3m – so look for it in the next class.

 Finally, the major class, called the normal class or galena type, is represented as 4m3m2 which is abbreviated as m3m.  The name hexoctahedral or holohedral may be found.  A lot of collector type minerals are placed here.  I include thirteen examples below but there are nearly 30 very well-known species in this class.

 Species           Space Group                         Forms                                                              twins?

Copper            Fm3m             cube, octahedral, dodecahedra,tetrahedra.                          twins

Gold                Fm3m             octahedral, dodecahedra, cube                                             twins

Platinum          Fm3m         cube (often isoferroplatinum and then twins, Pm3m.              twins?

Halite               Fm3m             cubic                                                  

Galena            Fm3m             cube, octahedral, cobo-octahedra                                         twins

Fluorite            Fm3m             cube, octahedral, dodecahedra                                            twins

Spinel              Fd3m               octahedral, cube, dodecahedra                                            twins

Diamond         Fd3m               octahedral, dodecahedra, cube                                            twins

Grossular        Ia3d                 dodecahedra, trapezohedra (garnet grp)               

Sodalite           P43n                dodecahedra                                                                        twins

Analcime         Ia3d                 trapezohedra                                                                        twins

Microlite          Fd3m               octahedral                                          

Pollucite          Ia3d                 cube, dodecahedra, trap. (rare)

 Well, now we should list a few others.  Silver, lead, iron, alabandite, magnetite, argentite (acanthite pseudos), gahnite, franklinite, chromite, pyrochlore, and uraninite all belong here.  Also, all the garnet group like almandine, andradite, pyrope, spessartine and uvarovite are best included here.  So, the best group for further study is the so-called normal group since we find so many minerals we all enjoy and probably have in our collections.  Based on the source I chose to use, I think the data here is more or less correct and up to date. 

Color in Beryl

By Bill Shelton

Color in Beryl

We should consider the fact that a pure beryl has no color-causing element in its formula.  Beryllium, aluminum and silicon do not turn out to be among the various elements that usually impart color to a mineral.  In nature, we can occasionally find examples where beryl is identified as white, colorless of nearly colorless.  The examination of some of these samples shows the absence of a few elements that are typically present in beryl which does exhibit color.  We should be especially aware of iron, manganese and chromium because these elements do impart color to the vast majority of specimens we see in collections and dealer stock. 

Let’s start out with the variety emerald – the color we usually see is attributed to a trace of chromium in the traditional sense and more recently to vanadium or even a combination or the two.   In one analysis, an emerald from Chivor, Columbia was noted to have 0.14% (by weight) chromium.  Another example, from Rhodesia, was recorded as having 0.28 to 0.59% chromium which can be compared to a further sample from the Ural mountains in Russia where results state .04 to .38% chromium were present.  So, we should conclude there is quite a range of values reported but what the absolute limits may be are not clear and may be subject to change with more reports being issued all the time.  Consider the unusual data for a piece from Zambia:  it has a value of .01 for vanadium, .07 for chromium and .73 for iron.  In spite of the mixture present, the color is said to be a nice emerald green.  Analytical results suggest the values for chromium in synthetic emeralds may be higher than the values seen in natural examples. 

 Red beryl, which has been assigned a few other names, is a rare variety known from a handful of localities.  Crystals are small and can be pale to intense in color.  The data available indicates the color is due to the presence of trace amounts of manganese.  One report lists the value at .08% which can be compared to another variety, morganite where the values are often lower.  Chemical testing shows red beryl may contain traces of titanium, zinc, tin, chromium, cesium, lithium, rubidium, boron, zirconium, niobium, lead and others.  I dare say beryl from most other places does not have a list like this; it also is odd that red beryl has essentially no water while most all pieces of other types will have water from .76 to over 2.5%.  The most noted location seems to be the Wah Wah Mountains, Utah but even the Topaz Mountain area has been noted as a source of similar pieces.  The common associates in the area include bixbyite, hematite, calcite, fluorite, garnet, hyalite, pseudobrookite, quartz and topaz. 

Morganite, a pink variety of beryl, is noted to contain small amounts of manganese and the color is attributed to it.  Besides containing manganese, morganite often also has alkali rich chemistry and this does not seem to affect color but may influence the habit (tabular) that is common in this variety.  While an orange colored type exists, it may be a bit unstable and reports say that these pieces will slowly alter to pink with exposure to light.  When a yellow tinge is present in morganite, heat treatment may remove it and improve the color to a better pink. 

Aquamarine may be the most desired variety for gemstones due to acceptance by customers, availability and price.  Here, color is attributed to iron; blue shades are caused by iron 2 in the channel site and this is the classic color for aquamarine.  Some sources also include green in the aquamarine sector and then we find color is due to iron also.  The difference is that both iron 2 and iron 3 are present.  This green color seems to be especially common in both ordinary beryl and gem grade material. Heat treatment may improve the green color to a better blue because the iron 3 is driven off and only blue will remain.  You may not be aware of it, but heat treatment is far more common that one may think. 

 If a beryl contains only iron 3, it will be yellow and perhaps called heliodor.  We find this variety to be less common than aquamarine and less desirable for gem use.  The color may range from golden to brownish yellow and the rarely seen deep shades are very pretty but still not widely offered as gems.  Some greenish samples are also sold as heliodor and here we can quibble about exactly what colors are acceptable under this variety – it seems to me that as one might expect, the definition for any variety may be a bit flexible. 

I referred to colorless and white beryl in the beginning – the varietal name goshenite is used here and it implies there is no trace element chemistry causing color in the example.  Well, as usual, it may be a bit more involved since iron 2 in the octahedral site and iron 3 in the channel site do not impart color to the mineral.  The presence of alkalis and other trace elements also do not add color.  So, a clever individual will see that the so-called pure beryl may just be lacking chromophores and not be technically pure.  An indirect piece of evidence is hidden in fluorescent data for beryl.  Here, mostly we find all types are inert or usually so.  Some goshenite, some emerald and a few morganites do fluoresce.  These are the very ones that are likely to be relatively iron-free.  When we consider the varieties aquamarine, heliodor and red beryl, they are all inert to fluorescent light.  Green beryl seems to behave in the same manner.  As you may know, iron is often described as quenching fluorescence in a great many mineral species. 

Colors in Garnets

By Bill Shelton

Colors in Garnets

Perhaps, we can find 10 major colors in garnets that belong to the six main species recognized by many sources.  What are the colors and which species are noted to occur in those colors?  Well, it appears that as one might guess that red is most common and will be seen in five out of six species.

The six species we refer to are almandine, andradite, grossular, pyrope, spessartine and uvarovite.

Red is never seen in uvarovite but will occur in all the others.  Pink is noted for three species – they are andradite, grossular and pyrope.   Orange, a nice color for garnet, is present in grossular and spessartine.  Yellow will likely occur in andradite and grossular.  Green, a personal favorite, is noted in andradite, grossular and uvarovite where it is also the only color to be seen.  Purple is unique to pyrope; however there are hints in certain almandines.  Brown, not a collector favorite, can occur in andradite, grossular and spessartine.  Black is mainly noted for andradite but a few grossulars may be this color.  Colorless garnet would be a rare thing in a general sense; pure grossular does exhibit this color now and then.  White rarely is found and when it is, expect the species pyrope and grossular to be present.  So, the winner is grossular with a total of 15 different shades.   I suppose uvarovite is the big loser with only one shade.  Almandine has three, andradite has eight, spessartine has six and pyrope has four.

The exact cause of the various colors is suggested to be due to chemicals present in the garnet.   Iron may impart red and yellow-green; yellow, orange and black (often with titanium); also purple when chromium is also present as well.   Chromium is also thought to cause green and notably in uvarovite where this is the only color we see.  Vanadium will be credited with yellow-green; manganese is responsible for pink and orange.  You may note that more than one cause is given for some colors.   The odd alexandrite effect may be due to chromium, vanadium and manganese together.

Various sources list the following colors for grossular.  They are pink, red-brown, orange, yellow, pale green, emerald green, greenish-blue, colorless (or nearly so), olive green, cherry red, dark green, honey brown brown orange-brown and black. I find the colorless and white garnets to be a peculiar thing – the explanation is said to be due to the lack of chromophores and is limited to pyrope and grossular when they are pure.  There is no iron or manganese; also no chromium or vanadium which all can be suspected causes of color in garnets. 


Bright Colors

By Bill Shelton

Proustite, Pyrargyrite, Pyromorphite, Mimetite & Vanadinite

I can write pages on all five species - for a collector, they all matter since availability is fair or better and all will brighten most any display.  According to mindat.org, here are the locality numbers for this group.  Proustite – 698   Pyrargyrite – 1,300   Pyromorphite – 1,510   Mimetite – 993   Vanadinite – 605.   The first two are the least common and, unfortunately, rather expensive members of this group.  For classic localities, one should consider the examples given below.  Proustite and pyrargyrite are especially noted from Andreasbrg, Freiburg and Pribram.  Also, Bolivia, Chile and Mexico.  U.S. localities include Colorado, Idaho, Nevada and New Mexico.  Cobalt, Ontario is also important.  Pyromorphite, with the most given localities in the group, is noted from Ems, Pribram, Beresovsk, Cumberland and Leadhills.  U.S. localities include Phoenixville, PA and Idaho.  Mimetite can be found from Tsumeb; Australia is another possible choice.  Mexico is famous as well.  Vanadinite can be found from Morocco and Africa amongst other worldwide localities.  U.S. localities are very common in New Mexico and Arizona.  I have found Morocco to be a very prolific source and one could buy as many as one wanted with ease. It may have the fewest localities but it seems to be the most available. 

 Color is a major concern and I suggest buying the brightest, pure shade you can find.  For example, vanadinite from Morocco is often an unpleasant hue with orange and/or brown mixed with red.  Get yourself an excellent pure red specimen.  They occur on black matrix and, as such, can be very dramatic.  The case lighting will affect the appearance so pay attention when selecting case lights for your samples.  As some of you know, red is a scantily represented color in the mineral kingdom.  The very best proustite can be a vivid red but exposure to light may darken them so keep that in mind.  Small crystals with excellent color have been recently available from Morocco but large, excellent crystals are very rare.  Chile produced some of the best pieces; these will likely cost a lot!

 I do not cover micromounts much in my articles but here we can find affordable representatives of most all the 100 species in this series.  You can find modest pyromorphite examples in Massachusetts and Pennsylvania with a little luck even today.  In the past, Connecticut produced examples at Canton and Thomaston (pyromorphite) but mostly micro size crystals.  A cursory glance suggests some, and perhaps all of these five species can be found in any size range.  The last three are likely to be more moderately priced. 

 A couple years back, I helped prepare and sell about 30 large boxes of mimetite.  They were white to clear, mostly small crystals; all were on dark matrix from Mexico.  Hundreds of samples were sold; the market seems to have absorbed them all; this is actually a typical circumstance.  Samples were highly lustrous and glittered when placed under any type of light.  You may already have one in your collection. 

 Some minerals seem to be stellar examples of misdirection, etc. and, as such, present a collector with perplexing problems; noteworthy might be turquoise.  Rarely have I encountered obvious defraudulent specimens within this group under consideration here.  I have seen pink fluorite and spessartine samples where additional small crystals were glued onto the matrix to provide a “better:” specimen.  None of this has, so far, been seen with these species.  In the event a specimen looks too amazing to believe, examine it with care for obvious glued connections.  A black light may be useful in this respect.  Much has been said regarding fakes and frauds before – you can check on the internet for a detailed report on this topic.

 Incidentally, all of the five species are good indicators of possibly valuable ore deposits.  Proustite and pyrargyrite are often associated with silver deposits worldwide.  Pyromorphite is found with lead and even zinc deposits but it only contains lead.  Mimetite, which is noted for lead, also contains arsenic.  Finally, as the very name suggests, vanadinite will contain vanadium; it also has lead in its formula.  Generally, we would consider vanadinite as a source of vanadium and a minor lead ore.


Azurite and Malachite

By Bill Shelton

Recently, we held a class on the two species listed above – apparently a few people thought it was a good lesson and would like a short review of the highlights on the website for TGMS. 

 I think the associated species are worth knowing about and please note six are found with both azurite and malachite.  They are cuprite, tenorite, calcite, chrysocolla, copper and wad – all according to Dana texts we consulted.  Azurite also may be seen with Fe oxides and chalcedony.  Malachite may come with chalcocite or limonite.  Of course, there are others but these are perhaps the most common and well-documented associates.  We also find pseudomorphs are commonly noted and for azurite we include azurite after cuprite, cerussite, tetrahedrite and gypsum. In the case of malachite, it is noted to replace azurite and cuprite.  There are others as well but they are probably less common or widely known than the examples given. 

Chemistry is one good way to compare minerals and here we find a great deal of similarity – they are both basic cupric carbonates.  For your own benefit, take a look at the formulas on mindat.org or in your favorite textbook.  While azurite has 69.2% CuO, malachite has 71.9%CuO – a minor difference.  Malachite has, upon chemical testing, shown to contain occasional traces of zinc.  Azurite is in contrast, ordinarily quite pure. 

Because of this, you may expect the properties to be even more similar than they are – the actual results may be a bit surprising.

 Clarity is dissimilar in that azurite is transparent to translucent while malachite is translucent to opaque.  This will best describe the majority of samples one may encounter – exceptional examples may be good additions to your collection.  Crystals of malachite are rare and almost always twins.  Azurite, on the other hand tends to be common as crystals and here twins are rare.  Color is quite different and azurite is azure blue to very dark blue. Most malachite is a bright green and may also be deeper shades that approach black which will sometimes be seen in banded pieces and also on crystals when they are found.  Micro size crystals are noted to be green and transparent but such material is not usually seen.  Malachite is also likely to be massive and can be botryoidal in form.  Azurite is often in crystals but botryoidal and stalactitic forms occur as well. 

Using mindat.org, I found that malachite has 5,478 photos and 11,798 localities.  Azurite has 6,274 photos and 5,340 localities.  An area of controversy concerns the type locality for azurite – some claim it to be Chessy, France but I am inclined to say there is no type locality because, as it says for malachite, it was known since antiquity.  You should look at the lists for the localities given on mindat.org – there is a lot of valuable data here. 

According to Minerals and their localities (2015) malachite is “a very common oxidation product of chalcopyrite and other secondary Cu sulfides occurring with azurite and some other secondary Cu minerals in gossan.  It is widespread throughout the world”.  Azurite is a “very abundant product of oxidation of Cu sulfides and it nearly always accompanies malachite.  The Handbook of mineralogy lists aggregates to 9 cm and exhibiting several forms (maybe 20 or so) for malachite.  They list crystals to 30 cm for azurite with typically complex crystals and over 100 forms.  You should look at the Mineralogy of Arizona for the long lists that they contain – you will find a lot of places for both species on a county by county basis. 

We do not make a huge effort to cover gem data but it seemed appropriate to do so and chose several sources. First, the Color encyclopedia of gemstones, where we find azurite as a source of rare faceted stones, mostly less than a carat but cabochons may be up to several inches.  Malachite is virtually unknown as a faceted stone but cabochons and carvings are very frequently observed.  If faceted, the stone would be under ½ carat and opaque. As you know, we do not usually bother to facet a stone when it is not quite transparent.  Masses to 50 tons are also noted, so we should take that fact into consideration.  Fluorescence, in multiple sources is said to be non-existent. 

 As a final note, we can find information as to what causes the two species to be different colors.  It seems that the structure is different enough to affect the absorption of the copper ions and perhaps the bond size as well so that azurite produces a blue color unlike the green we see in malachite.  In 1979, Marfunin said the structure in azurite was arranged so that the copper ion was in elongated octahedral coordination while malachite was in octahedral coordination – the difference may translate to bond length and that can cause a slight change in the absorption and color you actually see.

Collection Building

By Bill Shelton

Collections might seem to have a life of their own, but that is not the case for many of us. We have a plan of sorts that helps guide us when it comes to acquiring and managing samples in our cabinets.  Exactly how can an individual proceed?  What are some of the many decisions they may make to expand and mature their own collection?

This can be a very complex process; we may not be doing the same things as other collectors.  Living here in Arizona, it is likely that you at least think about a suite of minerals from here – but do you also choose certain places; i.e. Bisbee and Ajo or places in a particular county like Pima?  Maybe the selection process will involve a chemical context such as lead bearing species or perhaps secondary minerals (that will involve a chemical signature) and again you can limit the choices to certain areas.  One can easily do a collection of unusual crystal forms or more or less common species from little-known localities. 

Did you ever go to mindat.org and just enter Bisbee or Ajo and see what pops up?  Well, when I did there was a very brief list for “Bisbee” and prominently displayed we find 326 species and varieties and almost no other places were included.  Ajo on the other hand will show pages of worldwide places that contain “ajo” anywhere in the name and among them is Ajo, Arizona with 127 species and varieties listed.  In terms of worldwide localities, Bisbee ranks very high based on the number of noted species and varieties.  As a collector, you may decide to try and get all the macro size species or only the rarer species found in selected localities. It is all about choices and what you determine you would like to do. As one can see, a collector might choose to build a collection of all the species that are found in both of these districts.  There will be quite a few since the deposits are somewhat alike and azurite is famous from both as an example. 

We found 286 valid species for Bisbee and 100 for Ajo – also there are 6 type minerals for Bisbee and 2 type minerals for Ajo.  One can see where this may lead – type collecting has always been a part of our hobby. Besides, you only need to get 8 specimens.  You may already see that it is a trap of sorts since that will be easier said than done.  Add a few type species from other places and you are on your way to a new collection or perhaps a new sub collection.  How many places have odd or unusual quartz crystals here?  That can be a topic to investigate and perhaps you will add it to the growing collection you are creating.  I bet you will have a lot more than eight samples if you choose to do this!

As for me, I seem to have this penchant for former Soviet Union minerals and that is a lot of area and species to cover, but it does focus me away from collecting everything.  Among the many items, I have a small suite of odd eudialyte group minerals and seem to think it is a good idea to get more of them if they ever come available.  I also feel a need to get as many different Dalnegorsk minerals as possible in macro specimens and with hopefully decent crystals present – as you see, I must be picking and choosing, but then you get to omit things you really don’t care to have anyway.  But the disease is never cured since I must have twenty or more beryls form the Urals and so on and so forth.  So, why so many beryls you may ask?  Well, I like them, and why not if they please me?  After all, you make up the rules for what will be in your collection and then follow or change them to suit yourself.  

The number of pieces you may have can be an issue.  It has been said that some collectors add one and get rid of one so they keep the same number of species in the collection.  Well, I seem to add but not get rid of much and think a lot of you do the same thing.  After all, the best collections are in museums and heaven knows how many they may have. Well, actually I do know – the American Museum of Natural History has about 100,000 minerals according to their website – it seems to me like a lot more may be there. They also claim 3,700 gems and actually have 5,000 minerals on display.  So, we now know that it is imperative to go to New York and see all 5,000 of them for ourselves.   According to data from the internet, the Smithsonian in Washington, D.C. has 413,616 records (for specimens) and has 560 type mineral specimens.  The Sorbonne in France has 13,000 samples with 1500 on display.  The University of Manchester (Manchester Museum) states that they have some 17,000 specimens of meteorites, gemstones, ore samples and rare minerals. I also found the British Museum claims to have 80 million specimens including minerals and much more.

Did you realize that a great many pieces came from private collectors in the past? Even today, we see collectors sometimes choose to donate their pieces to museums. So there is another thing you can think about doing at some point.  If you ask a museum, they might tell you what they want and then you can work together to achieve a goal. They will probably like to have all the type material and a full set from Bisbee will no doubt be of interest too.  As a cautionary note, museums do reject donations when the specimens are not sufficiently good to achieve their purposes.  You should plan ahead if you have a notion of donating away your collection at some time in the future.  With a good plan, you help build their collection just as you have built your own.  

Collecting Eudialyte

By Bill Shelton

Eudialyte is a proper mineral species and the name of a mineral group.  There are 26 species within the group; I find about 20 are very restricted in their occurrence meaning they are present at only one or two localities.  The chemistry and structure of most of the species have only been studied in detail in the last 10 to 15 years.  Variability in the chemistry was noted over 100 years ago and this is one reason why we now have so many species.  In some ways, this is reminiscent of the similar circumstances surrounding the tourmaline group.  Fortunately, the name of that group (tourmaline) is not currently accepted as a mineral species.  As a collector, I am interested in similarities and differences between species within a mineral group.  The locality data is also significant to me; for the eudialyte group many species occur within the former Soviet Union which is my main collecting focus.

Based on webmineral and mindat, I have found the dates for all 26 species in the eudialyte group.  They are, indeed, a new group because all of the species were identified since 1990 with one exception.  Eduialyte dates to 1801 and has been accepted for a very long time.  The next entry is in 1990, and that would be alluaivite.  Three more were accepted in 1998: they are kentbrooksite, manganokhomyakovite and oneillite.  In 1999, we add khomyakovite.  All the rest are in the 21st century. So, 20 species might be called relatively new.  Few groups can claim this status.   

Color may be one of the most interesting properties among minerals; many collectors value it above most any other trait.  I decided to try and create a list of all the colors suggested for eudialyte, the species [as presented in a number of different sources].  They are red, pink, rose-red, carmine red, cherry red, orange-red, brownish-red, orange, yellow, yellow-brown, greenish-yellow, green, violet and brown.  When I collected at Mt. St. Hilaire, there were red, pink and orange crystals which we assumed to be eudialyte.  Only occasional eudialyte group members and then perhaps only certain examples of other group members exhibit colors not already listed for eudialyte the species.  I find color to be unreliable and probably misleading in the identification of the 26 species included in this group.

The proper identification of any eudialyte group member will be a complex process. As the scientific community moves toward structural mineralogy and site occupancy for species, the mineral collector is somewhat left in the lurch.  One good aspect (if you like more species) is this: new species identifications based on structural differences have resulted in many new species being described.  In 1990, there were two species in this group; by the year 2000 we had six.  Currently, the total is up to 26 (or more) and that is worth factoring into your collecting plans.  Identifying the 26 members is a challenge; the following article will briefly describe the members and their chemistry as well as noting some important locality data.  You probably need X-ray data, site occupancy information and detailed chemical analysis to positively identify a given species in the eudialyte group.

The chemistry of eudialyte is in a word, scary or so it seems to me.  Is there a mineral group that contains about half of the elements of the periodic table besides the eudialyte group?  One reference, Khomyakov (2008) claims this to be a fact.  I can confirm at least a third of all elements are at least occasionally present in the 26 group members.  My claim is based on published analytical data from multiple sources but is not to be considered as exhaustive or necessarily complete. The difference is possibly composed partly of additional REE’s that I have not found in the references searched so far.  Based on the ideal formula (see Back, 2014), you might assume that it would be easy to separate the 26 species; I’m not so sure it will be a simple matter. In the ideal formulas as given in Back (2014) there are 18 elements plus REE and vacancy.  The total chemistry is even more complex; see table 1 below. 


Table #1    Elements in eudialyte group minerals.

Al    Ba    C    Ca    Ce    Cl    Dy    Er    F    Fe    Gd    H

Hf    K    La    Mn    Na    Nb    Nd    O    P    Pr    S    Si    

Sm    Sn    Sr    Ta    Ti    W    Y     Yb    Zr


Rastsvetaeva et al (2012) refers to “isomorphic substitutions at several structural sites”, p. 496.  The descriptive notes for the sites are non-equivalent in various sources but the version below is hopefully correct.   The N sites (there are 5) usually host Na; K, Sr, Ba, Mn, Ca, REE, Y, H3O, H2O, Ce and vacancy are also noted as possible occupants.  The four M sites may contain (M1) Ca, Mn, Na, Sr, Fe and REE.  (M2) may house Fe, Mn, Na, Zr, Ta, Ti, K, Ba and H2O.  (M3 and 4) may contain Si, S, Nb, Ti, W, Na, Ce and vacancy.  The Z site houses Zr, Ti, Nb, Al, Fe, Mn, W and vacancy.  The O’ site contains O, OH, and H2O.  The “Si” site contains Si and Al.  The X (1 and2) sites contain Cl, F, H2O, OH, CO3, SO4, AlO4, and MnO4.  Jonhsen et al (2003) states that “a wide variation in chemical composition” (p. 786) is present in the eudialyte group minerals; further he claims “the theoretical number of mineral species based on the non-silicate cations only, extends far beyond several thousands”, (p. 788).  This may turn out to be a much more difficult project than we have time to resolve.  The general formula would look like N 1-5, M 1-4, Z, Si, O’, and X but see Rocks and Minerals, Vol. 89 (2014), Rastvetaeva (2012) or Johnsen et al (2003) for more detailed information.  Also, see the site data example under the description for kentbrooksite.

Solid solutions, either complete or partial, are widespread in the eudialyte group minerals.  Examine and compare the ideal formula for zirsilite-(Ce) and carbokentbrooksite – you will find (Na,Ce) in carbokentbrooksite while zirsilite-(Ce) has (Ce,Na).  This is typical of solid solution minerals and shows relationships fairly clearly.  The names kentbrooksite and ferrokentbrooksite are considered to be the Mn and Fe analogues but you will notice another difference.  Some REE is present – but only in the ideal version of kentbrooksite.  We can speculate that a series may extend from REE bearing to REE free examples in addition to the Mn-Fe series.  Alluaivite, rich in Ti, suggests a partial series might extend toward some Zr rich (the usual state) eudialyte species.  At least a few possible new species might exist at least theoretically.  Khomyakovite, richer in iron, and mangankhomyakovite, richer in manganese, offer another example of a series.  Via multiple substitutions, several species can be considered as members of solid solutions, also called solid solution series.  Just by manipulating the Fe and Mn, in ideal formula terms, there are possibly a dozen more new species.    Occasionally, we find a eudialyte described in terms of percentages of various species.  For example, Chakrabarty et al (2012) describes hydrothermal eudialyte from Sushina as “representative of the solid solution series between kentbrooksite- taseqite-Ce-zirsilite”.  Rastsvetaeva et al (2012) states “the relative amounts of the alluaivite, eudialyte and kentbrooksite structures in rastsvetaevite are about 50, 40 and 10 % respectively” on page 495.  This is another way to describe a specimen.  As a collector, I would like to be able to label the sample as a species in common usage today.

One of the slabbed specimens that is in my collection is from Khibiny; according to RAMAN data, it is ferrokentbrooksite.  This is very interesting to me and I hope the results are accurately portraying the sample.  Associated species are lorenzenite, nepheline and aegirine.  The label claims it is from the Partomdor mine; maybe actually the Partomchorr Mt.?  The specimen is a fair match to the description given by Yakovenchuk et al. in Khibiny (2005) on page 77.   Arem indicates “faceted gems well under one carat in size have been cut from Quebec material.  They are deep red and extremely rare.”  This material is possibly from Kipawa, Quebec; however Arem indicates Mt. St. Hilaire is a source for facetable material.  I have seen cabochons and lapidary slices of eudialyte with various minerals such as lorenzenite, nepheline, aegirine and agrellite etc. from Canada and Russia, the spheres and eggs made from this material are all quite interesting and occasionally spectacular.  If you decide to buy any of this material for specimens or lapidary use, find out what it might look like and where it is said to come from.  Use the internet to help determine if photos are available and then compare the appearance and stated locality.  Choose your dealer wisely since you will probably be relying on his expertise and supply chain to be reasonably sure that you get what you expect.  As always, a fine crystal is preferable to a grain or mass if you have the choice.  Not all species will be available as nice crystals. 

Finally, a note about rare earth elements: defined in different ways, I will use the list from Wikipedia.  There are 17 REE’s: Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu.  Many have been documented within various eudialyte group minerals.  Refer to Back (2014) and you will see several members of this group have REE; several more have Ce (cerium) in the ideal formula too.  At least nine species fall within this category based on the criteria given above.  

In summary, a collector faces some difficult choices when purchasing eudialyte group minerals.  From my perspective, I see many more or less massive examples that may or may not contain variable percentages of the rarer species.  Of course, a fine crystal is always a better specimen but will you lay out, say $250 or more for a sample that will be partially consumed in a more or less definitive study that may cost several hundred dollars more?  Probably, one needs chemical and structural data to be near positive of the correct identity of a given sample.  That sounds to me like it will be quite expensive and perhaps not worth your efforts.  As noted repeatedly in my brief species descriptions, there is very complex chemistry and variable amounts of components.  If one or more elements start to rise in terms of weight percent, the possibility exists that you have a different species; perhaps even a new species!  The samples themselves will often be intergrowths with two or perhaps more species present and intimately associated.  This is characteristic for this group of minerals. 


By Bill Shelton

If we consider a crystallized well-formed example of any mineral in comparison to the bulk of the crust, it will be infinitesimally small in terms of percent.  Hence, it could be characterized as rare.  A mineral collector often has a different slant on things and may refer to rare species or rare habits; also rare from a certain locality.            

RARE: May mean distinctive or uncommon as it applies to minerals.  Similar to infrequent; also may imply choice such as the best piece.                        

Amongst various factors affecting rarity and our perception of rarity consider the following possibilities.   A rare element may greatly restrict how much of a certain mineral exists – then consider how much might actually be identified and recovered.  Then, what quantity gets into the “mineral marketplace” and ultimately becomes available to you, the collector.  Further, will you be aware of the few dealers who may have this “rarity”?  Minerals that may be considered rare on the basis of chemistry might include minerals found to contain certain rare elements, perhaps in significant quantities as seen in their formulas.  Certain rare elements, however, have quite a few commonly found minerals readily available for sale.  Rubidium, #22 in rarity, has essentially no mineral examples where it is present in much quantity because it tends to be dispersed in low amounts in other species such as the feldspar group.  Bismuth, #70 in rarity has almost 150 mineral species – a huge number for such a rare element. Bismuth can be found as a native element and in species like bismuthinite. Rarity for elements is a number from 1 to 92 based on the relative abundance in the earth’s crust.   See the 2011 Gem and Mineral Almanac Section V: Elements and mineralogy for more on this topic.

Now a real factor to deal with is the mineral marketplace.  If you can’t find a sample for sale perhaps it is simply unavailable rather than truly rare.  Maybe there are only a few examples of the mineral known to exist.  That sounds like it might be really rare.  Examples exist where a single specimen is known –they certainly qualify as rare.  A few minerals are only known from one or a few places – they may be rare but not necessarily.  Consider charoite from Russia – essentially none exists elsewhere but a collector can buy a dozen pieces at most any major mineral show – never mind online.  One locality minerals may be rare-it might be dependent on the number of pieces available for sale rather than anything else. 

If location is factored in, rarity takes on a new appearance.  Some minerals are almost never found at particular places.  They can be described as rare from that place.  A collector can go to mindat.org and get a number for each species that suggests how many places it has been recorded from.  Similarly, quality can affect our perception of rarity.  A number of minerals rarely produce very fine crystal groups even though they are common species.  These minerals, then, are rare as fine specimens.  Crystal size can also be used.  Large, perfect crystals for many species can be few and far between even for minerals that are relatively common.

A gwindel of quartz may be rare from some places but collectors generally discount quartz as a rare species due to the ready availability of ordinary specimens and the fact that it is found at so many localities.  Yet, a large, perfect gwindel will not be easy to find.  So, when you hear that something is rare, listen for an explanation.  It is my impression that “rare’ is probably overused and incorrectly applied with regard to mineral specimens.  Also, bear in mind that sellers can use the concept of rarity to influence potential buyers.  Texts in our field use the term rare in a relative sense.  For example, Dana’s Manual of Mineralogy (1971) lists rare hydrous carbonates on page 325 and includes aurichalcite.  On page 415, aegirine is said to be relatively rare.  Page 471 tells the reader pollucite is a rare isometric mineral.  Mindat.org lists 869 places for aurichalcite, 989 for aegirine and about 150 for pollucite.  Compare these to, say, diamond with 696 localities or charoite with only 9.  I would like to add that none of these is rare in the marketplace in my opinion.