TELLURITE, A TELLURIUM OXIDE

The element tellurium is a silver-white metalloid (possesses properties of both metals and non-metals) with the symbol Te and the atomic number of 52 (number of protons in the nucleus of the atom). Tellurium exhibits oxidation states of 6+, 5+, 4+, 3+, 2+. 1+, 1-, 2-; however, only 6+, 4+ and 2- are stable. Tellurium can act as a cation with a 4+ oxidation state (IV) as in the uncommon mineral tellurite, TeO₂, or with a 6+ oxidation state (VI) as in jensenite, Cu₃TeO₆-2H₂O.   The telluride anion with a charge of 2- can combine with gold and silver cations in the minerals calaverite (AuTe₂) and sylvanite (AuAgTe₄); both minerals form major gold ores at Cripple Creek, Colorado.

Tellurium is an extremely rare element as most rocks contain about 3 parts per billion and is 8 times less abundant than gold. Tellurium is rarely found in a native form in rocks of the earth’s crust. MinDat listed 135 valid species containing essential tellurium: 1) 1 element; 2) 71 sulfides and sulfosalts; 3) 2 halides; 4) 44 oxides; 5) 13 sulfates; 6) 1 phosphate,1 vanadate, and 1 arsenate; and 7) 1 silicate.  So, most tellurium minerals are oxides and sulfates.

I previously posted about emmonsite (February, 13, 2017), a fairly rare iron (ferric) tellurite [Fe₂(TeO₃)₃-2H₂O], about the only tellurium mineral in my collection.  However, I recently picked up a specimen of the oxide tellurite, although certainly I feel out of my comfort zone in describing it. It was collected in 2000 by David Shannon (Arizona).

This is the best I can do with the photomicrographs!  The largest crystal (up or left), appears hexagonal and is only about .33 mm in length.  perhaps it is zemannite?  The dark green minerals attached to this large crystal may be denningite.  The really tiny acicular, straw yellow crystals are tellurite.

The specimen comes from the Moctezuma Mine (Bambolla) Mine, Moctezuma Municipality, Sonora Mexico.  It is a hydrothermal, gold-tellurium mine that produced a bonanza of tellurium minerals in the oxidized zone, something like 15 new species plus several previously named. The problem with my specimen is that all crystals are extremely small, less than one mm in length, and beyond the capability of my digital microscope.  However, they are visible (barely) in my binocular scope. The tellurite crystals are acicular or needle-like, light or straw yellow to light tan in color, less than adamantine in luster.  The tiny crystals are in “tuffs” or scattered, are translucent, and have a measured hardness of ~2.0 (Mohs). The quartz matrix also contains two other types of crystal that are larger and more robust than tellurite, and of a different color (green to brown), are striated, and some are terminated (pyramid-like).  My best guess is denningite [(Mn,Ca,Zn)Te₂O₅].  The other unknown appears to be hexagonal and might be zemannite [Mg₀.₅ZnFe(TeO₃)₃-4.5H₂O].  My mineralogical capability with these tiny crystals is lacking!  But, I have learned much from this little exercise.

Anyone who stops learning is old, whether at twenty or eighty. Anyone who keeps learning stays young. The greatest thing in life is to keep your mind young.  Henry Ford

BYE BYE DICK'S ROCK SHOP; WORMY ALUNITE

There are many items that are disappearing from the U.S. society.  Some are downright gone such as transistor radios while others are on a steep slippery slope—such as Windows 7.  No one misses the former while large masses moan about losing Windows 7, missing out on versions of Windows 8, being pushed screaming into Windows 10.  However, rockhounds, tourists, school children and a variety of others are tearing up about losing “mom and pop” local rock and mineral stores—they are fast going by the way of teepee-themed traveler’s lodges. 

A fancy portable transistor radio with leather case (hidden).  Most of my radios were AM only.  Photo from EBAY.

In my numerous decades of traveling around the country I had a tough time passing up rock and mineral stores, especially if they had added highway attractions like a petrified lizard or something.  I always pestered my father to stop at the stores while visiting Colorado or whizzing down U.S. 66 and I actually have a few minerals purchased in the 1950s. At any rate, rock and mineral stores were, at one time, numerous attractions along tourist highways and byways.  I miss them.


In 2006, after moving to Colorado Springs, I was pleased to locate two “old timey” stores, Ackley’s, and Dick’s; both had started in the 1970s.  I spent a good many hours down at nearby Ackley’s since the owner, Mr. Ackley, was an interesting person and always had an answer to my questions.  His major passion, however, was stamps and I enjoyed looking at his collection.  Ackley’s closed a few years ago and now Dick’s Rock Shop down in south Colorado Springs in Fountain is also closing the blinds in the near future.  Diana Wing, the proprietor of Dick’s, told me this was their 42^nd year in business but the Covid 19 pandemic was just too much of a loss to handle.  In addition, like me she is in the high rick category and does not want to take a chance of contacting the virus.  Currently Diana is trying to liquidate the inventory and is taking customers (reserve ahead and wear your mask) one at a time.  If you want to get a final mineral or two contact Diana at 719-390 7788 and get an appointment.  I have been down for a visit a couple of times and picked up some interesting items for my collection.

Dick's Rock Shop in Fountain, Colorado.

Now, do not misunderstand me--there are still plenty of places to purchase minerals.  The internet is full of “minerals for sale” and there is always EBAY.  However, it is pretty much buyer beware at some of these web sites.  There are some very reputable online dealers that have a sterling reputation.  Dakota Matrix up in Rapid City, South Dakota, was one of the first dealers to establish an online presence. Shannon and Family Minerals in Arizona has an amazing online inventory.  Check out the advertisements in a professional magazine like Rock & Gem to locate reputable dealers and learn if these dealers sell online or have brick and mortar sales.  And, then there are always the shows (except this year), big and small, that offer just about everything.  There are still a variety of store front dealers; however, some handle more exquisite minerals and cater to more discerning collectors.  The Denver area has Dave Bunk and Brian Lee with the latter selling museum-worthy specimens in 5 figures.  Locally, Canon City has the Gold Mine Rock Shop west of town, Nathrop has the Rock Doc, and the Rock Hut is in downtown Leadville—all have nice reasonably priced selections.  What I am missing is driving down a country two lane highway and suddenly there is a shop selling minerals, turquoise (always in the west), and trinkets, with a petrified dinosaur for the kids to see.  These are the small time, mom and pop stores where selling rocks and minerals is a labor of love and the front yard of the store is filled with large piles of rose quartz, obsidian, etc. priced per pound with a warning sign that these minerals are sharp and will cut your pinky. I love these many stores in the Custer-Hill City-Keystone section of the Black Hills in South Dakota.


So, what nifty specimens did I pick up down at Dick’s?  In a posting on October 9, 2014, I had a note about atacamite, a fairly rare copper mineral collected mostly in a few localities in southern Australia and coastal Chile (see posting fro environment of deposition, etc).  The chisel-end crystals vary in color between a very dark, blackish green and a light, bright green.  The mineral is soft (3.0-3.5 Mohs) and brittle with a vitreous luster.  The transparency varies between translucent (in the dark green variety) and transparent (light green specimens). Collector crystals are slender, prismatic, and striated, and/or tabular (others are massive or fibrous).  MinDat noted that atacamite may alter to malachite or chrysocolla.

These 2-4 mm crystals show the green color of atacamite; however, the vitreous luster of the crystals confuses my digital camera and does anot allow good photomicrographs.

Very dark green atacamite crystals from Copiapo, Chile.  Width of specimen ~4.1 cm.

 

 

 

 

A bundle of olive green libethenite [Cu₂(PO₄)(OH)] a copper phosphate often associated with atacamite.  Bundle about 2 mm in width/length.

So, I really did not need another specimen; however, the price was right, and the crystals are beautiful.  Home it came.  Besides, atacamite is interesting as a member of the Halide Group where one of the halogens, something like bromine, iodine, chlorine, or fluorine are the major anions.  These anions (negative charge) combine with cations (positive charge) like sodium (NaCl, halite or salt), calcium (CaF, fluorite), potassium (KCl, sylvite), or copper with a hydroxyl radical thrown in (atacamite).  The latter mineral is a secondary mineral oxidized from other copper minerals and in Chile formed in an arid and saline condition.


I am not much of a geode collector but could not resist a silver dollar size, mostly solid, specimen label Sonora Alondra Geode, Sonora, Mexico.  Now, I know where Sonora is located, but “Alondra?  No idea.  The reason for the purchase is in examining the small hollow center I noted three different sizes of quartz crystals: a tiny druse covering the sides, an intermediate, non-gemmy size, and then two larger, water clear, gemmy, crystals.  The latter were even more clear than Herkimer Diamonds.  And, there were some complex habits in the crystals, and one gem was double terminated. There is just a hint of amethyst color in the clear crystals.  I could not pass it up for a buck and a quarter. 

Crystal clear, gemmy, purple tinted quartz enclosed in a druze-lined vug in a Sonoran geode.  Note the reverse scepter quartz crystal (top).  Width of photomicrograph ~1.1 cm.

As for the location? Somewhere in Sonora!  I have seen similar geodes advertised on web sites with the water clear quartz; however, not much locality information was released.  I am certain that collectors of Mexican geodes know exactly where this geode was collected.

Prismatic crystals of mimetite each ~ 1mm in length.

Most specimens of mimetite in my collection have a botryoidal or spherical habit.  However, at the rock shop I picked up an absolutely beautiful group of golden orange, transparent, prismatic mimetite crystals with pyramidal terminations. Mimetite is a lead chloroarsenate [Pb₅(AsO₄)₃Cl], a secondary mineral that usually forms by the oxidation of galena [PbS].  The specimen came from the famous Santa Eulalia Mining District in central Chihuahua, Mexico.  The District is part of a large Carbonate Replacement Deposit that includes many of Mexico’s famous polymetallic mines.


The Summitville Mine in the San Juan Mountains of Rio Grande County, Colorado, has received much attention during the last three decades, not for its minerals and ore, but for the environmental damage caused by acid water drainage. Rocks containing the copper-gold-silver ore at the mine are hosted by the 22 Ma. South Mountain Volcanic Dome that is mostly composed of a quartz-rich latite (an extrusive volcanic rock) with feldspar (orthoclase?) phenocrysts. Additional magma underneath the dome later released gases rich in sulfur dioxide that migrated along fractures toward the surface, condensed into a sulfuric acid liquid, and leached much of the country rock.  Left behind was a vuggy silica progressing outward into various other zones.  Hydrothermal solutions arrived latter with various metallic minerals.

Placer gold was discovered, perhaps by 1860, in the San Juan Mountains while lode gold was found at Summitville in 1973 and the race was on to establish claims. Mining continued off and on at Summitville until about 1959 with production of ~258 ka troy ounces of gold.  In 1984 an open pit mine was constructed and a large heap leaching operation using cyanide commenced with production until 1992 of ~295 ka ounces of gold.  But then the mining company closed the mine, declared they were insolvent, and left the mess to the U.S. government.  Taxpayers then spent over 150 million dollars of Superfund money cleaning up the site.  In the meantime, water had leaked from faulty heap leaching pads and the company left with leaking retention ponds.  All of this very acidic water ended up in the Alamosa River draining into the San Luis Basin.


The specimen from Summitville is some sort of an extrusive volcanic rock that I presume is from the vuggy quartz zone, the alteration product of quartz latite; however, I am far out of my comfort zone here.  What is interesting about the rock is the mass of terminated quartz crystals that are arranged in a jackstraw fashion—sticking out in every which direction.  OK, but then the nifty secondary mineral inserted on open spaces between the tiny quartz crystals is composed of spheres of what appear to be tabular plates.  But there are also “worm” arrangements of the tabular plates that are fascinating.  I know that “worm” is not a crystal habit, but that is the shape of these tabs.  My best guess for this secondary mineral is alunite [KAl₃(SO₄)₂(OH)₆], formed by acidic solutions (probably created by pyrite or acid sulfate solutions) altering orthoclase feldspar. Alunite is tough to identify if it does not appear as translucent to transparent, soft (~3.5 Mohs), white to various shades of gray to cream, pearly small crystals (usually rhombohedral to pseudo-cubic).  Even then a rockhound needs to examine the environment and surrounding rocks.  It becomes more difficult if the alunite habit is fibrous, massive, or tabular.  The best I can tell is that the “wormy” masses are stacks of tabular crystals.  MinDat lists alunite as occurring at Summitville but does not provide photographs. Patton, 1917) described submillimeter tabular crystals of alunite intimately associated with quartz. Eckel and others (1997) noted that massive alunite is widespread in Colorado and often occurs in enormous quantities.  They also pointed out that sodium my replace the aluminum and if that replacement exceeds 50% the mineral becomes natroalunite; both varieties are present at Summitville.  

Jackstraw arrangement of terminated quartz crystals with light tan spheres of alunite.  The dark mineral is perhaps covellite, a copper sulfate.  The quatrz crystals are around 1 mm in length.

As above, but note the "wormy" habit of masses of tabular alunite crystals.

Finally, I picked up an ore specimen from the Black Cloud Mine at Leadville.  I really did not need the specimen; however, the price was right, and it was attractive with galena, dolomite, sphalerite, quartz, pyrite, and chalcopyrite.  The Back Cloud was located about 10 miles east of Leadville near Mt. Sherman at a high elevation (11,499 feet) and was the last working polymetallic mine in the Leadville District but closing in 1999 after a 31-year run.  The Leadville District is located in the Colorado Mineral Belt where mineralization in Paleozoic carbonates (dolomite at the Black Cloud) came from solutions associated with Tertiary intrusions. Lead and zinc were the primary minerals of interest at Black Cloud; however, copper, gold and silver were also in production.

Sphalerite and dolomite.  The dolomite is covered by a tiny quartz druse best seen on the center rhomb.

Dolomite and sphalerite. Rhombs are ~ 1mm in width/length.

Pyrite crystal.  Dull gray mineral is galena.

Chalcopyrite.

Galena (gray), sphalerite (black), and dolomite.

So, just as the Black Cloud bit the dust and disappeared (virtually nothing left on the surface today), Dick’s Rock Shop is also leaving after a long run.  Dick’s opened the same year as Ackley’s, 42 years ago, but outlasted them by a few years.  Both shops had proprietors who would spend time with visitors and answer questions.  Both had the classic, old timey, glass showcases stuffed with white cardboard boxes containing a variety of minerals (often dusty) with cheap to reasonable prices.  If you want to get in on the final sale, head to Fountain and Dick’s.  Be certain to thank Diana for the memories.

REFERENCES CITED

Eckel, E. B., and others, 1997, Minerals of Colorado: Fulcrum Publishing, Golden, Colorado and Friends of Mineralogy—Colorado Chapter, Denver.


Patton, H. B., 1917, Geology and ore deposits of the Platoro—Summitville mining district, Colorado: USGS Bulletin 13.