The Micromount Corner

Figure 3 – Malachite - Maid of Sunshine Mine, Arizona (25 X magnification)

In some specimens of Malachite several different crystal morphologies can be seen in close proximity to each other. In the specimen shown in Figure 3 we see a “Jackstraw” arrangement of acicular Malachite microcrystals placed just above a collection of blocky looking crystals made up of many slender acicular Malachite crystals all parallel to each other. The color ranges from dark green (almost black) to a light bluish green. This specimen is also from the Maid of Sunshine Mine, Gleeson District, Dragoon Mountains, Cochise County, Arizona. (25X magnification) unaware of the hidden wonder that can be found even in the most common of minerals with just a hot mug of tea, some patience, a little careful investigation and a good stereo microscope. A whole world of wonder lies waiting to be discovered. I encourage those of you who have not tried mineral micromounting to give it a try, you will be amazed at what you may discover.

Greetings everyone. This month we will be investigating micromounts of the mineral beryl. Chemically, beryl is a beryllium aluminum silicate. There are several varieties exhibiting minor chemical impurities which cause specific wavelengths of light to be absorbed resulting in a very strong color to the mineral. Listed below are the most common varieties of beryl and their colors:

Green: Emerald
Pale Blue: Aquamarine
Red: Bixbite (Also called red beryl)
Pink: Morganite
Greenish-Yellow: Heliodor
Colorless: Goshenite

The red variety of beryl is the only one that occurs as micro-crystals. The topaz bearing rhyolite of the Wah Wah Mountains in Utah is the most common location for red beryl. Although pricy, micromounts of red beryl are readily available from mineral dealers. There is something almost mystical about the deep red color of red beryl, particularly when strongly illuminated under the microscope. The other
colored varieties of beryl are much more difficult to obtain as micromounts. I have found some very small gemmy crystals of morganite, the pink variety of beryl in the topaz bearing rhyolite at Topaz Mountain, Utah. These are rare and you need to break down a lot of material to find one. Aquamarine is the most readily available variety of beryl, but still difficult to find in gemmy crystals. Much of the aquamarine specimens I have seen have been pale blue opaque crystals. By far the real prizes for micromounters are gemmy crystals of emerald, the deep green variety of beryl. Occasionally you will find a mineral dealer with good “in matrix” thumbnail specimens of emerald crystals. These can be broken down to make some very fine micromounts. However, be prepared to pay a princely sum for the specimens. Specimens from the Columbian emerald mines afford the best specimens. Shown at right is a photomicrograph of a gemmy micromount of emerald from the Muzo Mine in Columbia. (Photographed with Kodak 400 color print film at 50X with white LED illumination – 4 second exposure.) Although beryl represents a challenge to the micromount collector, when you find a fine specimen it adds immeasurably to your collection. At the upcoming mineral shows, I will be prowling the mineral dealer tables on the look out for some fine beryl specimens for micromounts. See you there. Until then may all your skies by blue and may all your vugs be crystal filled.

Greetings everyone; this month I would lke to highlight one of my favorite micro mineral subjects, the mineral legrandite. Chemically this mineral is a hydrated zinc arsenate hydroxide. The type locality for this mineral is the Flor de Pena Mine, Lampazos, Nueva Leon, Mexico. Current thinking is that legrandite forms under very special conditions by the action of arsenic bearing secondary solutions on weathering zinc deposits. This is a rare mineral being found in only a few localities in the world. Legrandite is highly sought after by collectors of micro minerals because of its beautiful straw yellow color and well formed prismatic crystals. Shown below is a photomicrograph of legrandite on matrix from the Ojuela Mine, near Mapimi, Durango, Mexico. Notice the Monoclinic prismatic 2/m crystal habit with the wedge shaped crystal terminations. (Photomicrograph at 25X with 4 second exposure on ASA 400 film.)

Legrandite is named after the Belgian mining engineer, Mr. Legrande. The mineral appears in several crystal habits ranging from slender acicular prismatic crystals to the large prismatic crystals with wedge shaped terminations shown in the above photomicrograph. Good specimens of legrandite are hard to come by on the collector market. Be prepared to pay a princely sum for good specimens. One of the interesting aspects of legrandite is the prevalence of sub faces on crystals. In the photomicrograph shown below a small crystal below the two large wedge shaped crystal terminations. This smaller crystal shows some of the smaller facets on the crystal termination. (Photographed at 50X with a 4 second exposure on ASA 400 film.

I have found that Legrandite specimens from the Ojuela Mine near Mapimi, Durango, Mexico yield the best transparent “gemmy” crystallized specimens. I have purchased Legrandite specimens from a number of mineral dealers. Another interesting aspect of Legrandite specimens from the Ojuela Mine is the complex vuggy matrix on which the crystals are formed: A complex combination of tubes, stringers and botryoidal masses with a mind blowing combination of pinks, browns and yellows. Sometimes I think the matrix is almost as interesting as the mineral crystals. Countless enjoyable hours can be spent exploring the miniature world under the microscope with the Ojuela Mine specimens. It is fun sometimes to imagine that you have shrunk down to a size that would fit on the specimen and are literally “walking the specimen”.
I would be interested in hearing of your own adventures when exploring the miniature worlds of micro-minerals. You can reach me at: d.babulski@comcast.net. Until next month, may all your skies be blue and all your vugs be crystal filled.

Dana, E.S., A Textbook of Mineralogy, John Wiley & Sons, Inc, New York, Fourth Edition, Pages 390 - 392.

Grafe, Markus; Nachtegall, Maartin and Sparks, Donald,
Formation of Metal-Arsenate Precipitates at the Goethite-Water Interface, Environ. Sci. Technol., 2004, 38, 6561 – 6570.

Lindgren, W., Mineral Deposits, McGraw-Hill, New York, Second Edition, Pages 99; 871-874.

Internet References:
http://webmineral.com/data/Legrandite.shtml
http://www.mindat.org/min-2365.html
http://www.xtal-dbeals.com/Ojuela_2.htm
http://10.1911encyclopedia.org/M/MI/MINERAL_DEPOSITS.htm

One of the striking aspects of the mineral world is the large variety of colors that minerals present. One of the most striking of these colors is the pink to red of the cobalt arsenate hydrate mineral erythrite. Cobalt deposits often feature erythrite as a secondary mineral from alteration of the primary cobalt minerals such as the siegenite (cobalt nickel sulfide) and linnaeite (cobalt sulfide). This mineral is called "Cobalt Bloom" by miners and is used to indicate the presence of cobalt ore minerals. Its pink to red color is distinctive and stands out against the drab coloration of the host rocks. The mineral gets its name from the Greek, erythros for "red".

From the micromounters perspective erythrite is somewhat rare but produces striking specimens. At mineral shows, I have found that this mineral fetches a princely sum for really good micromount specimens. In micro form the mineral forms flattened monoclinic form plates, usually a transparent pink or red color. As the crystals become larger, the mineral becomes less transparent and deeper in color. It is interesting that erythrite forms a solid solution series with the nickel arsenate annabergite. The crystal form for both minerals is almost the same. The photograph shown below is of erythrite from the Aghbar Mine, Bou Azzer, Anti-Atlas Mountains, Morocco. The mineral was photographed through the microscope at a magnification of 30X with Fuji ASA 200 color print film using a white LED as the light source and a 4 second exposure.

Although good micromount specimens of erythrite are a bit hard to come by, the beauty and unique color of the mineral makes a must have for the micromount collection. I have found that the easiest specimens to obtain and that have good micromount potential are those form the Bou Azzer area of Morocco.

Until next time may all your skies be blue and may all your vugs be crystal filled.

The element arsenic (As) is located on the Periodic Table of elements in the same semi-metal band as the elements boron, silicon and tellurium. As such, the element arsenic exhibits similar characteristics to the other semi-metals. Silicon for example, when combined with the element oxygen forms the silicate (SiO2) radical. This unique combination of the elements silicon and oxygen bonds with a bewildering array of other elements to form the large number of silicate minerals. Likewise when the element arsenic is combined with oxygen, it forms the arsenate (AsO4) radical. Like the silicate radical, this unique combination of the elements arsenic and oxygen bonds with a large number of other elements (mostly metallic in nature) to form the large number of arsenate mineral species.

Interestingly enough, the metallic element copper (Cu) bonds readily with the arsenate combination and forms the bulk of the arsenate mineral species. For the micromounter this is a fortuitous situation as there are a number of well-known primary copper mineral deposits
where arsenic bearing hydrothermal fluids have reacted with the primary copper minerals under oxidizing conditions forming the secondary copper arsenate minerals. Most of these unique mineral species only crystallize in micro form. One of more well known of these mineral occurrences is the Tintic Mining District in Utah and the Antelope Mining District in Nevada. When more than one of the copper arsenates are present in one specimen, the color and variety of crystal form is just awesome. In the Gold Hill Mine in Tooele County, Utah, the copper arsenates conichacite, strashimirite and mixite occur together in one specimen.

The photographs at right show these three minerals in one specimen. A careful analysis of this specimen shows that all three of these copper arsenate minerals did not crystallize at the same time, but most likely represent subtle changes in the chemistry of the hydrothermal mineralizing fluids. Strashimitite, which is a copper arsenate hydroxide penta-hydrate, appears to have been deposited first, followed by conichalcite and then mixite. Chemically speaking, conichalcite is a calcium copper arsenate hydroxide and mixite is a bismuth copper
arsenate hydroxide tri-hydrate. The mineralizing fluids appear to have become enriched in calcium and bismuth as the minerals were being deposited. What is really cool about these specimens is the conichalcite. This mineral occurs as bright green spherules. A very close examination under the microscope of these spherules shows them to be hollow spheres of conichalcite. It is unknown at this point if the hollow spheres are actually filled with fluid. It is also interesting to speculate on how these hollow spherules formed. In this image, ball like sprays of green acicular strashimirite and light blue mixite populate the matrix.

In this image, conichalcte, strashimirite and mixite are all present on the matrix.

(Both photographs above are courtesy of Dave Babulski from his collection. They were photographed with Kodak ASA 400 film at a magnification of 25X. The light source was a white light LED.)

So for some real interesting micromounting adventures you can't beat those magnificent copper arsenates. Most of the mineral dealers carry copper arsenates from a variety of localities. Those from the Tintic Mining District in Tooele County, Utah are among the finest. Until next time, may all your skies be blue and all your vugs be crystal filled.

This month we will investigate the mineral CAVANSITE. As mineral species go, cavansite is a relative newcomer, being officially recognized as a mineral species in 1967. The type locality is the Owyhee Dam, Lake Owyhee State Park, Malheur County in Oregon. The host rocks in this area are Miocene volcanics consisting of massive rhyolite and andesite. The cavansite occurs as minute, rather unimpressive, crystals in gas cavities in the volcanic rocks. As this mineral occurrence was rather unimpressive, cavansite was relegated to the status of a mineral curiosity until the early 1970’s when the mineral was discovered in the Deccan trap basalts in the Poona district in India. At this locality, cavansite occurs as well developed spherical aggregates of deep blue crystals associated with large crystals of stilbite in gas cavities in the basalt. This mineral occurrence created a sensation in the mineral collecting world. At mineral shows these days it is not uncommon to see rather awesome large specimens of stilbite festooned with spherical groups of deep blue cavansite from the Poona, India locality. The name of this mineral is derived from its chemical composition of calcium, vanadium and the silicate radical. The deep blue color is a result of the vanadium content. Good micromounts of cavansite from the Poona, India locality are very hard to find. You have to break down some thumbnail size specimens to get at the “Good Stuff”. The “Good Stuff” is relatively open radiating clusters of deep blue transparent crystals that occur in the void areas between large crystals of stilbite. Shown below are some photomicrographs of some of the “Good Stuff” extracted from thumbnail size specimens purchased from dealers at the December GMS show. Magnification is 25X. An interesting aspect that micromounters have is a visual examination of change in the intensity of color as the vanadium content in the mineral varies. Pale blue crystals with deep blue tips are just awesome things to look at. An examination of the recent mineralogical literature indicates that most geologists agree that vanadium in cavansitecomes from the host volcanic rocks. Reports of vanadium content as high as 600 to 750 ppm in the basalts near Poona have been presented by several geologists working in the area. Another interesting observation is the sequence of mineral deposition. Stilbite appears to have been deposited first, followed by cavansite. In some cases a third depositional phase of heulandite or calcite is observed as tiny crystals deposited on crystals of cavansite. All in all, some superb micromounts can be had by having the courage to break down thumbnail size material. I for one will be looking for some good thumbnail size specimens of cavansite at the upcoming spring gem and mineral show. There is a real thrill when you break down a larger specimen and find some of the ”Good Stuff”. Until next month, may all your skies be blue and all the vugs you find are crystal filled. (photos by Dave Babulski)

This month we will look at the mineral vanadinite. In the world of mineral micromounts, vanadinite, with its typical red color and distinctive crystal forms, is a favorite among mineral micromounters. I would hazard a guess that just about every mineral micromounter has at least one vanadinite specimen in their collection. Vanadinite is classed as a lead chlorovanadate and is the result of the action of vanadium rich hydrothermal solutions in the oxidation zone of primary lead sulphide deposits. Vandanite is part of a chemical series with the minerals pyromorphite and mimetite and these three minerals are sometimes found in the same mineral deposit. Pyromorphite is a lead chlorophosphate and mimetite is a lead chloroarsenate. All three of these minerals have very similar crystal forms, varying primarly only in color. Although the pure form of each is colorless or very pale yellow, vanadinite is primarily red, pyromorphite is primarily green and mimetite is primarily yellow. Vanadinite crystallizes in the Hexagonal-Tripyrimidal form. The most common crystal habits are:

Vanadinite was first discovered at Zimapan, Hildago, Mexico and is named for its Vanadium content. I have noted that most of the Vanadinite seen at mineral shows in the past year is from the Moroccan mines. Vanadinite specimens from other locations are available from dealers on the internet and via mail order but you really have to “dig” for them. An interesting aspect of vanadinite in micromount form is the reflection of light from inclusions and internal fractures in the crystal. Although this mineral is primarily red in color, light reflected internally comes out as yellow. I have found that some of the vanadinite from the Hamburg Mine, when brightly illuminated looks like it is on fire! Some of the vanadinite from Mibladen, Morocco when brightly illuminated shows a beautiful shiller from many parallel reflective planes in the crystal.

This month's installment of the Micromount Corner will address the "Wonderful World of Wulfenite". Named after the Austrian mineralogist, Franz Xavier von Wulfen (1728 – 1805), wulfenite is one of the most sought after micromount specimens. Officially classed as a lead molybdate, although other elements can sometimes substitute for lead, providing a range of mineral compositions. Like the mineral calcite, wulfenite crystallizes in a number of habits and appears in a wide range of colors from white to black and a whole range from yellow to red. There is even a green Wulfenite. This mineral occurs in the oxidized portion of zinc-lead deposits and as such is often associated with other colorful secondary lead zinc minerals. Fortunately for the micro-mounter, some of the crystal habits of wulfenite only occur as micro-crystals. The Fourth Edition of Dana’s Handbook of Mineralogy has some very nice drawings of the more common wulfenite crystal habits.

("Tips and Trips", Vol. XXXV/8, August 2006, page 12 & 13.)
Secondary Uranium Minerals – Part 1

Hello everyone, this month the Micromount Corner will begin a series on secondary uranium-bearing minerals. Generally speaking, secondary uranium minerals are brightly colored and make for some striking additions to a micromount collection. This month we will investigate three secondary uranium minerals that are often found together. These are the minerals, meta-uranocircite, schoepite and ianthinite. As is often the case with mineral micromounts, more than one mineral species can be found in a given specimen. Figure 1 is a photomicrograph at a magnification of 30X of the minerals meta-uranocircite, schoepite, and ianthinite. The specimen is from the
Krunkelbach Valley Uranium Deposit, Menzenschwand, Black Forest, Baden-Wurttemberg, Germany. The specimen was photographed through the microscope with Kodak ASA 400 color print film with a four second exposure. The microscope light source is a white light
emitting diode.

Figure 1

In Figure 1, the light green waxy looking mineral is the meta-uranocircite. Uranocircite is a hydrated barium uranium phosphate. The meta form is a dehydrated form of the mineral. This mineral is characterized by its green color and waxy appearance and tabular crystals that look very similar to the uranium bearing mineral autunite. The tabular greenish crystal of meta-uranocircite is surrounded by masses of bright yellow acicular crystals of the mineral schoepite. This mineral is a uranium oxide hydroxide hydrate and is highly radioactive. Both the metauranocircite and the schoepite are deposited on a dark brown resinous botryoidal matrix of the mineral ianthinite. Ianthinite is a complex uranium oxide deca-hydrate. All of these secondary uranium bearing minerals are on a light brown matrix of uraninite. Figure 2 is a closer view of the specimen photographed at a magnification of 60X

Figure 2
The Krunkelbach Valley Uranium Deposit was a series of uranium bearing barite-flourite veins hosted by granite. This deposit was worked until 1990. The dumps have now been removed and the area has been landscaped. The mineral uranocircite is named for its uranium content and the Greek for falcon – referring to Falkenstein, Saxony, Germany, where the mineral is commonly found. The mineral schoepite is named for Alfred Schoep (1881-1966), Belgian mineralogist who studied uranium mineralogy. The mineral ianthinite is named for the Greek ianthinos, “violet” as this mineral often has a somewhat purple coloration. Mineral species that are alteration products of primary uranium bearing minerals offer some interesting color and challenges to a micromount collection. Because these secondary minerals are often highly radioactive, care must be taken when placing the specimens in your micromount collection. Some mineral species are very sensitive to
radioactivity. Some collectors house all their radioactive specimens in special shielded containers. I encourage you to investigate these colorful mineral species.

("Tips and Trips", Vol. XXXV/9, September 2006, page 13.)
"MIXITE"

Greetings everyone, this month I would like to introduce you to a mineral that many micromounters refer to as “the blue-green fuzzies,” so called because the mineral occurs as radial groups of fine hair-like acicular crystals. This is the mineral mixite. On a list of rare minerals, mixite is certainly up near the top. You can count the number of mixite occurrences on the fingers of both hands. In the United States the arsenic bearing mineral deposits in the Tintic District in Utah are the most well known occurrence. Another well known mixite occurrence that yields excellent micromounts is the Majuba Hill Mine in Pershing County, Nevada. This rare mineral species has another distinction
in that it is one of the very few minerals containing the element bismuth.

Chemically, mixite is a hydrated bismuth copper arsenate hydroxide. The mineral forms in the oxidation zone of metal ores that probably contained primary Bismuth Sulfides such as Emplecite or Bismuthinite. Mixite was discovered in 1879 in Czechoslovakia and is named for the Czech mining engineer, A. Mixa.

Color varies from emerald green to blue-green. The fine color and unusual crystal form plus its rarity makes mixite a highly sought after mineral species for micromount collectors.

Most mineral dealers have good specimens of mixite, but be prepared to pay a bit for the really fine specimens. Shown in the photographs below are specimens of mixite crystal spays in vuggy quartz from the Gold Chain Mine, 300 foot level, Mammoth, East Tintic Mountains, Juab, Utah. The specimens were photographed through the microscope at 30X with Kodak ASA400 color print film with a four second exposure.