GRAB ME: CHRYSOCOLLA AND TENORITE

When we recognize the virtues, the talent, the beauty of Mother Earth, something is born in us, some kind of connection, love is born.

Thich Nhat Hanh

Sometimes, in examining a table or flat of minerals, something just reaches out and grabs you---take me home, take me home…The beckoning mineral need not be expensive nor rare nor exotic, just something of beauty in the eye of the beholder.  A table of minerals at a recent Tucson Show had one of those specimens that simply reached out and grabbed me.  It does not have showy crystals nor exotic minerals; however, the banding and colors commanded an allure.  So, it became “mine.”

Blue chrysocolla, black tenorite, with "silica" rind.Width of specimen ~5 cm.

The most striking minerals in the specimen are sky blue chrysocolla, a hydrated copper aluminum hydroxy silicate [(Cu, Al)₂H₂Si₂O₅(OH)₄-nH₂O but with a variable composition] intermixed with tenorite, a black copper oxide [CuO]. Also present are calcite [CaCO3], a banded light blue silicate such as chalcedony or perhaps silica-infused chrysocolla, and an unknown tan-orange-green mineral.  Some might call the specimen a geode or a broken vug. It was collected in the Boleo District, Mun. de Mulegé, Baja California Sur (BC Sur), Mexico. 

Reverse of specimen above: Ca=calcite, C=botryoidal  chalcedony, B=banded chalcedony, T=tenorite, ?=blue chalcedony; G=green"chalcedony.

Chrysocolla has been used as a semi-precious gemstone for centuries, often as a substitute for turquoise, but its internal structure is still not well understood.  For example, most mineralogy books and web sites believe chrysocolla belongs to the Orthorhombic Crystal System (Three crystallographic axes (A,B,C) of unequal length that make angles of 90 degrees with each other).  However, Frost and Xi (2013) point out that this assignment “remains uncertain.”  Some geologists believe chrysocolla is crystalline in nature while others believe it “generally amorphous” and therefore not a true mineral (strict sense) (Klein, 2002). Sun (1963) reported “chrysocolla is not a definite chemical compound but a hydrogel containing mainly SiO, CuO and H₂O, and minor amounts of Al₂O₃, CaO and MgO.”  Frost and Xi (2013) stated  “chrysocolla is a colloidal mineral…but questioned…whether chrysocolla is: 1) a mesoscopic [somewhere between microscopic and macroscopic, between big and small] assemblage of spertiniite, Cu(OH)₂, silica, and water; 2) represents a colloidal gel; or 3) is composed of microcrystals with a distinct structure.”  Their definitive study of chrysocolla, based on X-Ray Powder Diffraction, Raman Spectroscopy, and Infrared Spectroscopy studies, “concluded that chrysocolla is not based upon spertiniite but is an amorphous hydrated copper silicate…with a simplified chemical formula of CuSiO₃-2H₂O.” 

 

It would seem that an amorphous substance would not be classified as a mineral but as a mineraloid, most of which do not have a definite structure on the atomic scale (chrysocolla is never in visible crystals; www.minerals.net)   However, evidently some forms of chrysocolla have identifiable structures at the “nano-level” (crystals acicular; www.webmineral.com) and hence it has mineral (IMA) status rather than a mineraloid.  At least that is my interpretation of the situation and any other explanation is above my pay grade.

Chrysocolla has variety of colors but usually is some shade of blue and/or green—due to coloring by the major cation, copper (an idiochromatic mineral).  The streak on an unglazed porcelain ranges from pale blue to light green.  Chrysocolla is quite soft at ~2.5-3.0+(Mohs) and is a good property to distinguish itself from much harder turquoise at ~5-6 (Mohs).  Chrysocolla has a luster from ranging from earthy (dull) to vitreous to waxy and appears in solid and fibrous veins, in tuffs forming tiny crystals, commonly as massive or perhaps as encrustations, as rounded balls or botryoids, and even as stalactitic columns.  Most forms are opaque but thin slices are translucent and are fairly brittle when “hit.” 

Contrasting with the sky-blue chrysocolla is tenorite, a black copper oxide (CuO).  Tenorite would not be an impressive mineral with its earthy to dull to metallic luster and generally massive habit without common accompanying friends—chrysocolla, malachite and azurite.  It is opaque with a black streak and is brittle commonly with a conchoidal fracture.  It is soft at ~3.5 (Mohs).  I have only observed massive and botryoidal tenorite; however, some localities produce small crystals (Monoclinic Crystal System).  It appears, from my reading, that visible crystals are only formed when tenorite is the product of volcanic sublimation (crystallized from gasses around volcanic vents).  In fact, the type locality for tenorite is around Mt. Vesuvius in Italy.

Photomicrograph banded chalcedony left grading into blue chalcedony or silica infused chrysocolla surrounding black tenorite.  Notice green ?chalcedony encased in the blue.  Width of photo ~1.2 cm.

Photomicrograph of calcite in center of vug.  Width of photo ~ 1.2 cm.

Photomicrograph of banded chalcedony and tenorite.  Note botryoidal calcite in upper left quadrant.  Width of photo ~1.2 cm.

Reverse of specimen with silica rind, blue chrysocolla and black tenorite. Width of photomicrograph ~1.2.

Blue chalcedony and black tenorite.  Width of photomicrograph ~1.2 cm.

 

Blue chalcedony and black tenorite.  Width of photomicrograph ~1.2 cm.

Both massive tenorite and chrysocolla are somewhat common minerals in the oxidized zone of hydrothermal copper deposits.  It seems as if every copper mine in the western U.S and Mexico produces these two minerals; they are not uncommon.  As noted above, my specimen came from the Boleo District in Baja California.  The discovery locality, the Boleo Copper District located near the town of Santa Rosalia, has been the site of major sulfide mining (open pit until the 1980s) and at one time (at least in the 1950s) was the second largest producer of copper in Mexico (Wilson and Rocha, 1955). Underground mining started in 2012 with the first production in 2014 and I presume mining is still active.   As best I can decipher, the copper deposits are in an uplifted belt of Neogene (Miocene or Pliocene) rocks within the El Boleo Formation (deltaic and near-shore marine claystone-siltstone-sandstone beds).  The major sulfide ore minerals are chalcocite (Cu₂S) accompanied by chalcopyrite (CuFeS₂), bornite (Cu₅FeS₄), covellite (CuS), and native copper (Cu).  The oxidized zone (above the sulfide deposits) has a large variety of copper oxides, copper carbonates, copper silicates, manganese oxides, and rare halide minerals.

My geode-looking specimen has cream to white massive calcite in the center surrounded by botryoidal “silica”, perhaps chalcedony, and then grades into banded chalcedony? or perhaps silica-infused chrysocolla.  About all I can tell is the “silica” is much harder (Mohs) than the chrysocolla.  The banded chalcedony seems to flow around the tenorite and, at times, seems to grade into the chrysocolla.  The “rind” is a tan to gray “crumbly” or shattered microcrystalline “silica.”  There are many “things” I don’t understand about this specimen but am trying to “learn” additional facts to satisfy my curiosity. It turns out that a specimen I purchased since it grabbed me seems to have a complex history!  What more could I ask for?

REFERENCES CITED

Frost, R.L., and Y. Xi, 2013, Is chrysocolla (Cu,Al)2H2Si2O5(OH)4·nH2O related to spertiniite Cu(OH)2? -a vibrational spectroscopic study: http://eprints.qut.edu.au/58692/11/586

Sun, M.-S., 1963, The nature of chrysocolla from the Inspiration Mine, Arizona: American Mineralogist, v. 48.

Wilson, I.F. and V.S. Rocha, 1955, Geology and mineral deposits of the Boleo copper district, Baja, California, Mexico: U.S. Geological Survey Professional Paper 273.

DAYDREAMING ABOUT NATURE: MIXITE, FROM TINTIC, UTAH

Joys come from simple and natural things; mist over meadows, sunlight on leaves, the path of the moon over water. Even rain and wind and stormy clouds bring joy.

I often “daydream” as I write since remembrances of my past help me to contemplate the present, and brings joy to my life.  I may not remember where my truck keys are stored but have very sharp recollections of my time spent in the wilderness waters of northern Minnesota: As long as there are young men with the light of adventure in their eyes or a touch of wildness in their souls, rapids will be run.

A “long time ago” I satisfied two great personal “loves” by combining both teaching geology and canoeing in an outdoor classroom.  My first classes were held on the Current River in southern Missouri, a newly designated National Scenic Riverway (the first in the nation).  While interesting, it was not the wilderness area that I craved.   So, the next few years I moved to the Boundary Waters Canoe Area Wilderness (BWCA) in northern Minnesota headquartered in Ely.  At that time the great author, environmentalist and strong advocate for the protection of wilderness was still alive and living in Ely---Sigurd Olson (1899-1982).  I had devoured, several times, all of his books and still bring out The Singing Wilderness (a signed copy) for a yearly reading.  I figured that a man who took his wife canoeing on their honeymoon was my kind of hero, and Mrs. Olson was my picture of a strong spouse and partner. I did not take my wife canoeing on our honeymoon (the two days that it was—no money) but not long after I had her carrying packs over the portage trails in the BWCA.  Again, a strong spouse and partner.

I bring this up since the writings of Olson often just flow across my mind and present vivid pictures: The mist was all gone from the river now and the rapids sparkled and sang. Sometimes today the words associated with geology just sort off spin off my tongue and flow across my mind with vivid pictures: Ajax, Black Dragon, Black Jack Empire, Boss Tweed, Bullion Beck, Carissa, Eureka Hill, War Eagle, Scotta, Uncle Sam, Opoltonga, Humbug, May Day, Godiva, Sunbeam.  All of these locations, plus many others, are mines in the greater Tintic District in Juab and Utah counties in the central part of the state. I have not seen most Tintic mines but never-the-less can picture them in my mind and wonder about the names.  Was the “boss” of Tammany Hall, William Tweed, investing in Utah Mines?  Or was the mine owner or foreman an admiring Democrat? Did some miner hit a rich vein and yell Eureka?  Did a mine tunnel collapse and someone yelled Mayday?  Those are some of life’s persistent questions.  

Satellite image of Utah showing location of Tintic Mining District and Salt Lake City.  Image courtesy of Ray Sterner, Johns Hopkins University.

The Tintic District is located about 50 miles south-southeast of Salt Lake City on the west central slope of the East Tintic Mountains.  The mountains are part of the Basin and Range Physiographic Province and connect the Oquirrh Mountains to the north (also Basin and Range mountains and the range visible directly to the west of Salt Lake City) and the Canyon Range to the south.  

Google Earth image© of Tintic Mining District including Mammoth Mine.  Utah Lake is the large body of water in the northeast.

The Tintic Mining District was discovered in ~1869 and its geology/mineralogy was summarized by Wilson (1995) who noted the presence of ~175 species of minerals…”Much of the production of siliceous ore in the district [was] utilized by smelters in Tooele and Salt Lake City to mix with more iron-rich ores of Bingham.  Tintic has produced gold, silver, lead, copper, iron and zinc as its major commodities.”  Morris (1968) noted the primary ores consisted of “sulfides and sulfosalts of silver, lead, copper, iron, zinc and bismuth in association with jasperoid (silicified carbonate rock), barite, aggregates of quartz crystals, calcite, dolomite, and ankerite…gold is locally common…”

The geology of the Mining District is related to several large volcanoes that erupted in the Tintic area (and much of western Utah) during the early Oligocene (Hintze and Kowallis, 2009) and covered Paleozoic rocks that were folded and faulted by an earlier mountain building event termed the Sevier Orogeny (Cretaceous).  During the later Oligocene, these volcanoes begin collapsing and large calderas formed.  The hydrothermal solutions associated with the volcanics followed the cracks and faults in the Paleozoic rocks and helped dissolve portions of the limestones.  As these solutions cooled the minerals begin to crystallize forming the ore bodies in the limestone.

Although the Tintic mines currently are closed (although many are under claim), their total mineral production, about 20 million tons, would translate into about three billion dollars (2006 dollars).  The most valuable metals were silver (~42%), gold (29%), lead (17%), copper (~6%) and zinc (~6%).  Production peaked in the first half of the 2oth Century and finally ceased with the 2002 closing of the Trixie Mine (Krahulec and Briggs, 2006).   For a great history of the mine transportation network check out Railroads and Mining at Tintic at www.utahrails.net.

One of the smaller mines in the District is the Carissa, a mine found on the slope of Mammoth Peak, home of the well-known Mammoth Mine.  It was connected by a tunnel to its more productive neighbor the Northern Spy Mine. Carissa may not have been a large gold-silver producer; however, it was later (years?) a specimen producer of very nice crystals of the arsenates adamite [(Zn,Cu)₂AsO₄OH], conichalcite  [(CaCuAsO4(OH)], mimetite [Pb₅(AsO₄)₃Cl], olivenite [CuAsO4(OH)], mixite [Cu₆Bi(AsO₄)₃(OH)₆-3H2O)] and the copper carbonates rosasite and azurite.  All of these minerals are secondary and found in the oxidation zone where primary lead (argentiferous galena), zinc (hemimorphite?), bismuth (bismuth) and copper (copper, cuprite, enargite) were present.  The enargite could also have provided the arsenic for the arsenate (AsO₄) ion with a charge of Minus 3.

In an arsenate ion, individual arsenic atoms are surrounded by four oxygen atoms that form a strongly-bonded group that are linked together by weaker bonds involving the metal cations plus the hydroxyl ion (OH) and the water molecule (H₂O).  For example, in mixite the metal cations are bismuth and copper. In the agardite series (five minerals of the Mixite Group), there are numerous Rare Earth Elements (REE) serving as cations.

Goethite matrix with various minerals as listed below (except azurite).  Width of specimen ~5 cm.

A second specimen from the Cariss with visible azurite.  Width ~1.7 cm.  Matrix includes much baryte.

The most interesting specimen mineral collected from the Carissa, as least to me, is the rare copper bismuth arsenate named mixite.  Essentially a micromineral, mixite occurs as very tiny, slender acicular needles that often congregate together in tuffs or radial sprays. Although the crystals are usually some shade of green to blue-green, occasionally they are white to light blue.  Individuals appear to have an adamantine luster although this is a difficult call. The tuffs are more silky in nature. Crystals belong to the Hexagonal System and appear to be translucent to transparent.  Hardness is listed as 3.5-4 although that is tough for me to determine. 

The above eight photomicrographs are from specimens collected at the Carissa Mine.  M=mixite, B=baryte, C=single green "ball" of conichalcite, A=azurite, R=rosasite, G=goethite.  Each photomicrograph has a width 1 cm.

Mixite is the namesake of the Mixite Group, as assemblage of about a dozen arsenates or phosphates containing hydroxyl ions and water molecules but with different cations--all look similar and are difficult to distinguish between. I know my specimens from the Carissa Mine are mixite since they have been identified by X-Ray Diffraction (XRD) methods. 

Unknown mineral.  Note penetrating twin.  Crystal ~ 6 mm.

Flat-bladed green mixite crystals collected from Gold Hill Mine, western Utah.

How often we speak of the great silences of the wilderness and of the importance of preserving them and the wonder and peace to be found there. When I think of them, I see the lakes and rivers of the North, the muskegs and expenses of tundra, the barren lands beyond all roads. I see the mountain ranges of the West and the high, rolling ridges of the Appalacians. I picture the deserts of the Southwest and their brilliant panoramas of color, the impenetrable swamp lands of the South. They will always be there and their beauty may not change, but should their silences be broken, they will never be the same.

All quotes above are from the writings of Sigurd Olson.

REFERENCES CITED

Hintze, L.F. and B.J. Kowallis, 2009, Geologic History of Utah: Brigham Young University Geology Studies, Special Publication 9.

Krahulec, K. and D. F. Briggs, 2006, History, geology, and production of the Tintic Mining District, Juab, Utah, and Tooele Counties in R.L. Bon, Editor, Mining Districts of Utah: Utah Geological Association Publication 32.

Morris, H.T., 1968, the Main Tintic Mining District, Utah in Ore Deposits of the United States, 1933-1967: American Institute of Mining Engineers, Graton-Sales Volume, New York, v. 2. 

Wilson, J.R., 1995, A Collector’s Guide to Rock, Mineral & fossil Localities of Utah: Utah Geological Survey, Misc. Publication 95-4.