WULFENITE: THE BLACK SHEEP VARIETY

Arizona has many mines that have produced an amazing account of minerals.  Virtually every natural history museum in the world has displays of Arizona minerals, especially those related to copper—think raw copper, cuprite, azurite and malachite.  Out of these available minerals, collectors seem to focus on the widespread copper carbonate, azurite, and the less common lead molybdate, wulfenite, PbCuO4; both minerals are secondary in origin and are found in the oxidized zone. The azure blue azurite was often found in large pieces that make fantastic display specimens.  Wulfenite crystals are generally small, an inch is large, but occur in a wide variety of luscious red to orange to yellow specimens.  Museums collect azurite while mineral collectors and rockhounds “love” wulfenite.

Specimen #1.  Coronadite is massive dark gray material that is covering and replacing tabular wulfenite.  Where wulfenite crystals are exposed, most are clear to colorless.  Collected from the Glove Mine and are the famous "black wulfenites." Width of specimen ~4.0 cm.

Specimen #2 collected from the Glove Mine.  A mass of tabular wulfenite crystals, ranging from green to greenish-orange to clear/colorless to dark gray (pseudomorphs) in color. Width of specimen ~4.5 cm.

Wulfenite may be found in numerous Arizona copper mines and ranges widely in color and size.  But one mine in particular, the Glove Mine, produced fantastic specimens of “black wulfenite.”  Actually the “black” wulfenites are “regular” crystals that have been covered with, or partially/fully pseudomorphed to, the lead manganese oxide coronadite [Pb(Mn₆⁺⁺⁺⁺Mn₂⁺⁺⁺)O₁₆].  The transition metal manganese has a large number of oxidation states from +2 to +7.  In coronadite there are two oxidation states present, +4 and +3.  In some older articles one might read the black mineral on wulfenite is some other manganese mineral such as cryptomelane, pyrolusite or psilomelane; however,  it now appears that geologists have settled on coronadite.  The black (actually more dark gray) manganese minerals are notoriously difficult to tell apart without some help from a gizmo such as an XRD.

Above two photographs of Specimen #2 showing massive coronadite (C), wulfenite (W) tabs ranging from clear to completely black pseudomorphs. The coronadite also appears as singular botryoidal "globs" and botryoids "stuck together" An unknown tan to orange mineral (?) is also present ??(mimetite). Width of photomicrograph ~1.6 cm.

Specimen #2 Clear tabs of wulfenite along with a single tab showing a tan and black color.  That single tab may be zoned or simply showing a partial pseudomorphed crystal.  Width of photomicrograph ~ 9 mm.

Photomicrograph, Specimen #2, showing clear to partially colored wulfenite crystals with a dark gray matrix of coronadite.  Width ~1.6 cm.

Specimen #2 with clear square tabs of wulfenite, dark gray coronadite and a "glob" (center right) of an unknown mineral,  Note the very tiny, beyond my camera capabilities, of "fairy dust" covering the specimen.  Width ~ 1.9 cm.

Specimen #2.  Clear wulfenite crystals W1, partially pseudomorphed coronadite after wulfenite, W2, and broken tab of wulfenite, W3, less clear than W1. Width ~1.2 cm.

The Glove Mine is located about 50 miles or so southeast of Tucson in the southern Santa Rita Mountains, Santa Cruz County, in the Tyndall Mining District.  Olsen (1966) described the mine as having three different levels based on mineral assemblages: 1) the lower and primary sulfide zone contains silver-rich galena, pyrite, chalcopyrite, quartz and sphalerite; 2) above that level is a silver-enriched intermediate zone of cerussite, smithsonite, anglesite and minor wulfenite; and 3) the upper oxidized zone of cerussite, wulfenite, and anglesite.  Hydrothermal solutions associated with a Laramide (late Cretaceous ~75 Ma to early Tertiary ~65 Ma) intrusion moved along fault zones and deposited the lower primary sulfides. Minerals (often specimen minerals) of the upper oxidized zone were concentrated in solution cavities in the host late Paleozoic Naca Limestone.  Rasmussen (date unknown) noted that wulfenite never forms without the presence of the lead carbonate cerussite and the only molybdenum needed is that found in the ground water during leaching and oxidation.  In fact, wulfenite is rarely found in rocks containing the mineral molybdenite.

The lead carbonate cerrusite, a precursor needed for the formation of wulfenite (from the Flux Mine in Arizona).  The molybdenum in the wulfenite came from circulating waters during oxidation.  Width ~3.3 cm. 

William Ascarza of the Arizona Daily Star summed up the history of the Glove Mine (and associated holdings) in a 2016 article.  He noted that the first original claim was staked in 1911 after discovery in 1907 and primary sulfides of lead, zinc, silver, copper were mined along with a small amount of gold and molybdenum (from the wulfenite I presume).  During the early mining days, a mule team wagon transported the ore to the rail station a few miles west at Amado and then it was shipped to a smelter in El Paso, Texas.  Mining was mostly shut down between 1918 and 1951 but in the 1950s workers again begin excavation and produced about 5,000 feet of underground “tunnels” in the various claims.  The Glove was the richest of the claims as the ore averaged about 14% silver and 40% lead.   Mining continued, intermittently, for the next couple of decades with the ore now going to a mill in Demming, New Mexico, and later to the Tonto Basin Mill.  Excavation continued into the 1980s but sometime in that period (I think) shut down and a 2011 fire badly damaged the structural integrity and the mine is now closed but still under claim.

Wulfenite is generally a collector mineral although in quantity it has been used as a secondary ore of molybdenum.  Rockhounds appreciate the mineral for its classic thin and tabular crystals (there are other forms such as dipyramids, however) with beautiful colors ranging (usually) from yellow to orange-yellow to honey-yellow to reddish orange.  The Red Cloud Mine in Arizona has produced classic deep red crystals.  At times the crystals are less spectacular in color and appear as green, brown, gray and some are colorless. Crystal color seems related to impurities during formation. Crystals are usually vitreous to sub-vitreous in luster unless coated with manganese oxide or some other mineral.  Wulfenite is soft (~3.0 Mohs), has a white streak, and belongs to the Tetragonal Mineral System.  Individual crystals may be transparent, especially if thin, but darker colored and thicker crystals are opaque.   The brittle and thin crystals break easily and collectors are aware that a prized specimen must be protected.  

Wulfenite is in solid solution, and forms a series, with stolzite [Pb(WO₄)] since the MoO₄^{- -} and WO₄ ^{- -} ions are about identical in size and shape.  As I understand, most wulfenite has some tungsten and stolzite has some molybdenum in their chemical compositions.

Wulfenite is pseudomorphed by a number of minerals, including but probably not limited to: bayldonite (lead coper arsenate hydroxide), conichalcite (calcium copper arsenate hydroxide), dolomite (magnesium carbonate), malachite (copper carbonate hydroxide), mottramite (lead copper zinc vanadate hydroxide), smithsonite (zinc carbonate), stolzite (lead tungstate) (list from www.tsumeb.com) and quartz (silica dioxide), vanadinite (lead vanadate chloride), coronadite (lead manganese oxide).  I could not locate much information about the “cause” of such pseudomorphic processes. My guess is that a mineral, such as wulfenite, is produced under specific physical and chemical conditions and is stable.  With an interruption in these stable conditions a new mineral crystalizes but does not change the external shape of the original mineral.  In some cases, only a “crust” forms over the original mineral (is this a “real” pseudomorph?).  In other examples the original mineral is partially or fully replaced.  Any other knowledge about pseudomorphs is above my pay grade.

I think all rockhounds dream of hitting a bonanza of minerals in a “pocket”; however, that is a fairly rare occurrence.  Around Colorado Springs in the Precambrian pegmatites experienced specimen miners sometimes locate pockets of fabulous colored topaz crystals, or aquamarine crystals in pegmatites on Mt. Antero.  My friend, Mr. Rockhounding the Rockies, has been known to pull 40-50 smoky quartz crystals from a single pocket but on other days perhaps just a broken fragment shows up.

In reviewing information about the secondary mineral deposits at the Glove Mine I came across an article by Gene Shlepp describing his find of wulfenite crystals in one of the limestone solution cavities: “It is probably every mineral collector’s dream to have been able to collect wulfenite specimens in the Glove mine.  I was fortunate enough over the last fifty plus years to have been able to collect there. Sometimes the collecting was profitable, sometimes it was not.  Several times in the 1980’s and early 1990’s I had leased the mine [and was quite successful on one trip].  After thirty feet of mucking, we were able to reach the bottom of the old stope from the 1950’s. There we discovered an open cavity six feet long and approximately two feet high. The cavity was lined with fine thin yellow wulfenites up to 1 ½ inches.  This really made our hearts pound as we collected and packed the material in boxes. After taking them to the upper level of the mine, where they would be safe from anymore drilling or blasting we had to do, it was time for a couple of cold brews.”  Again, most rockhounds can only dream of such a find. 

Both specimens came from one of my favorite rock and mineral shops, the Tucson Mineral and Gem World on South Kinney in the southwest part of the city.  This is a "real" rock shop with lots of dust, flats of minerals, thumbnail drawers, less expensive specimens, and two very nice and talkative brothers who have been in business 50 years.  They encourage exploring the shop and "give away" specimens to young rockhounds.  It is worth a visit if you are in Tucson. 

REFERENCES CITED

Ascarza, W., 2016: www. tucson.com/news/local/mine-in-santa-ritas-was-big-ore-producer.

Olson, H.J.,1966, Oxidation of a sulfide body, Glove mine, Santa Cruz County, Arizona: Economic Geology, vol. 61.

Rasmussen, J., date unknown, Wulfenite in Arizona: www.janrasmussen.com/pdfs/Arizona%20Wulfenite.pdf

SCHOLZITE: & SEARCHING FOR THE EDIACARAN

In my continuing search for nifty arsenates, vanadates, and phosphates I ran across a specimen of the rare calcium zinc phosphate mineral, scholzite [CaZn₂(PO₄)₂-2H₂O)].  I was attracted to the specimen for a couple of reasons: 1) I had recently finished reading an article describing the many uncommon/rare phosphates (Type Locality for scholzite) collected from Hagendorf, Bavaria, Germany; 2) the phosphate minerals from the area are similar to the minerals collected from the lithium-bearing phosphatic pegmatites in the Black hills of South Dakota; 3) the numerous glassy, gemmy, terminated crystals of scholzite were impressive. The Hagendorf mines generally produced feldspar from the late 1800s until the 1980s (seems similar to Black Hills feldspar mines).  The pegmatites are mostly zoned intrusive bodies (~300 Ma) that were intensively weathered in the late Tertiary (~4-5 Ma) (Dill, 2009).  As I understand, scholzite can form as a primary mineral in late stage phosphate mineralization; however, it is more common as a secondary mineral in the oxidation zone of zinc- and phosphate-bearing pegmatites.

The specimen I purchased, however, came not from Germany but from another famous location in one of the Flinders Ranges in southern Australia north of Adelaide.  I am not very familiar with Australia but did recognize the locality, not due to the mining activity, but because of a subsection of the Flinders Ranges called the Ediacaran Hills.  Many decades ago, when I enrolled in Historical Geology, the base of the Cambrian Period (then established at ~600 Ma) was defined as the “beginning” of multicellular life.  This confused many learned paleontologists since Cambrian trilobites, among other animals, first appeared as diverse and complex animals.  In fact, they crawled around and had eyes---something one might not associate with a newly evolved group of animals.  In order to explain this sudden appearance of life, American paleontologist Charles Wolcott coined the term Lipalian Interval as a period of time between the younger Precambrian rocks and the oldest Paleozoic (Cambrian) rocks.  Wolcott believe the youngest Precambrian rocks (the time when animals evolved) had been eroded and no longer existed, or perhaps had not been discovered.  This position was easy to believe since in so many areas in the world, especially in the United States, the earliest Paleozoic rocks, commonly transgressive marine sandstones, unconformably rest on top of igneous or metamorphic Precambrian rocks. The text books of the time were full of photos of the Lipalian Interval, especially of rocks in the Grand Canyon where the regional unconformity separates rocks of the Cambrian Tonto Group from the Precambrian tilted and folded Grand Canyon Supergroup (and below that the basement rocks of the “Vishnu Schist”-- probably several different rock units in the schist).  John Wesley Powell, in his travels through the Grand Canyon, referred to the Precambrian-Cambrian unconformity as The Great Unconformity (essentially synonymous with The Lipalian Interval).

The Great Unconformity as described by John Wesley Powell during his 1870s journey down the Colorado River through the Grand Canyon.  Geologists then believed that a major unconformity separated Precambrian rocks from the overlying Paleozoic rocks on a world-wide basis.  Sketch courtesy of the US National Park Service.

The other unknown, or misunderstood, geological theory during my undergraduate years was the concept of “Continental Drift” (today known as Plate Tectonics).  We dutyfically studied Miogeosynclines and Eugeosynclines and really never understood how these features formed or operated.  In those days, most undergraduate students never questioned the wisdom of their instructors or the textbooks authors.  We were just beginning to hear about “drifting continents,” a theory developed in the first half of the century but certainly did not understand what mechanism drove the continents to “drift around.”  Then in the early 1960s seafloor spreading was validated and suddenly, a mechanism was available to move continents.  However, I really did not learn much about plate tectonics until enrolling in graduate studies, and even then, some of the instructors were non-believers.

Then “things” began to fall in place.  Geologists started to better understand plate tectonics and assigned the name active plate margins to areas where the plates were moving “forward” and then colliding with other plates resulting in “mountain building! Passive plate margins were the trailing edges of plates where tectonic activities were less active and where large volumes of sediments from entering streams, and deposition of marine rocks, were piling up on the wide continental shelves.  A great modern example in North America is to look at our west coast where mountain building, faulting, volcanoes and earthquakes indicate an active plate—the continental plate is banging into and overriding an oceanic plate(s).  The east coast provides an example of a passive plate where wide oceanic shelves are collecting sediments and lime rocks.  Of course, conditions change over geologic time and the badly eroded Appalachian Mountains were produced along an active plate margin in the late Paleozoic Era.

Active (west coast US) and passive (east coast US) plate margins.  Diagram courtesy of geologycafe.com at MiraCosta College.

And guess what?  In some of these passive margins around the world deposition continued from the latest Precambrian up into the Cambrian (now established as beginning ~542 Ma)--for example the Wood Canyon Formation in the Death Valley Region.  And the second guess what--- multicellular animal fossils were located in these latest Precambrian rocks.  The animals did not have skeletons but certainly had complex body plans---“like” jellyfish, worms, arthropods, fronds, bags and lots of unknowns!  Did these Precambrian organisms and their communities flourish into the Cambrian?  Probably not as they were replaced by skeletal animals in the great Cambrian Explosion, and perhaps even provided food for the early Cambrian animals.  But again, the question remains---what about the skeletal animals of the Cambrian?  They seem not closely related to the non-skeletal animals of the latest Precambrian, so……..?  One of life’s persistent questions.

Dickinsonia sp. from the Ediacaran Biota.  Public Domain photo.

Although fossils of these latest Precambrian multicellular organisms have now been found on every continent, geologists have named the community the Ediacaran Biota after localities in the Ediacara Hills of south Australia in the Flinders Ranges.  These fossiliferous sedimentary rocks were deposited along the passive margin of a “continent” that composed part of the Precambrian Supercontinent Rodinia.  In addition, in 2004 the International Union of Geological Sciences named the last period of the Neoproterozoic Era of the Precambrian (latest Precambrian) the Ediacaran.  Although absolute dates remain somewhat uncertain most stratigraphers place the beginning of the Ediacaran Period at ~635 Ma, commencing after the end of the global Marinoan Glaciation. The Ediacaran was the first officially approved geological period in 120 years.

The specimen of scholzite in my collection came from the Reaphook Mine in what Hill and Mills (1974) termed “near-surface mineralized zones in unmetamorphosed sediments of the Lower Cambrian Parachilna Formation…in the Flinders Ranges, South Australia. The mineralized zones have resistant ferruginous and manganiferous cappings, which grade downwards into complexly fractured phosphatic pebble conglomerates, sandstones, and siltstones. They seem to have developed as a result of the action of groundwater causing near-surface enrichment of manganese, iron, zinc, and phosphorus in fractured and faulted zones in the Parachilna Formation.”  Scholzite at Reaphook is associated with a number of other phosphate-rich minerals and the Mine is the Type Locality for another calcium zinc phosphate, hillite [Ca₂Zn(PO₄)₂-2H₂O].

The Flinders Ranges of South Australia have a long history of mining for zinc, silver, barite, lead gold, uranium and others.  However, most of these mineral deposits are located in the Northern Flinders Ranges and the Reaphook Hill is in the southern part of the Ranges.  About the only reference that I could locate about Reaphook is MinDat.org: “a zinc and phosphorus-rich deposit…it [was] mined for a few years for mineral specimens (mostly Scholzite).”  In addition, the 22 collected minerals listed by MinDat do not include anything that I would call a valuable ore mineral.

Scholzite (Orthorhombic) is an interesting mineral and could be mistaken for other vitreous, transparent to translucent, white to colorless, soft (3.0-3,5; Mohs) phosphates such as its dimorph, parascholzite (Monoclinic).  Scholzite commonly appears as radiating blades of crystals with pointed terminations, or as less-acicular tabular crystals.  The mineral’s rarity in being restricted to zinc- and phosphorous-rich rocks is an important guide to initial identification based on physical appearance.  Any in-depth identification probably requires the use of sophisticated electronic gizmos. I also find it interesting that this rare mineral is also found in the pegmatites of the Tip Top Mine in Custer County, South Dakota.

Scholzite crystals.  Width photomicrograph ~7 mm.

Scholzite crystals perched on matrix (goethite?).  Width of photo ~2.1 cm.

Photomicrograph scholzite crystals.  Width photo ~7 mm.

For my collection of somewhat rare and interesting minerals, I was happy to snag a small specimen of scholzite.  And I became even more excited to dredge up fond memories of my early learning about the existence of Ediacaran (AKA Eocambrian) rocks and fossils, not to mention passive plate margins and seafloor spreading.

REFERENCES CITED

Dill, H.G., 2009, The Hagendorg-Pleystein phosphate pegmatites (NE Bavaria, Germany) – A mineralogical, chronological and sedimentological overview: Estudos Geologicos, vol. 19, no. 2.

Hill, R.J. and A.R. Milnes, 1974, Phosphate minerals from Reaphook Hill, Flinders Ranges, South Australia: Mineralogical Magazine, vol. 39.

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.