CORNWALLITE: ANOTHER GREEN ARSENATE

Let us dedicate ourselves to what the Greeks wrote so many years ago: to tame the savageness of man and make gentle the life of this world.
                                             Robert Kennedy

The year 1968 was a momentous year in my life, as well as in the world.  I suppose that the events in my life were quite trivial as compared to what was going on in the world; however, I seem to remember both with clarity.  In world events, Martin Luther King and Bobby Kennedy were assassinated and the war in Southeast Asia seemed spinning out of control.  There were demonstrations across the U.S., especially at the institutions of higher education.  The Prague Spring ended abruptly as 750,000 Warsaw Pact troops brutally entered Czechoslovakia (anyone thinking Ukraine?).  I was a fan of Eugene McCarthy; however, the Democratic National Convention nominated Hubert Humphrey and Edmund Muskie.  The riots at this convention in Chicago seared my mind with images.  The Republican choices in the presidential election were Richard Nixon and Spiro Agnew.  George Wallace ran as an Independent.  Wow, talk about choices!  Apollo 8 astronauts were the first humans to see the back side of the moon.  The educated Chinese seemed a threat to leaders so they were being reeducated in the country.  Similar to today, the North Koreans were belligerent and seized the USS Pueblo.  It seemed to me that 1968 saw “a lot” of killing and hatred.  In the U.S. the demonstrations against the war were widespread and often turned violent.  Throw in the demonstrations associated with the Civil Rights movement and the country was in turmoil, but President Johnson signed the Civil Rights Bill.
We should declare war on North Vietnam. . . .We could pave the whole country and put parking strips on it, and still be home by Christmas.

Ronald Reagan, 1965

I was in my second year of graduate study at the University of Utah and was somewhat insulated from the turmoil.  In those years Utah was almost a theocracy and the war demonstrations seemed at a minimum.  I was just trying to “fit in” and do the best job possible.  My hair was sort of wild and curly and I sported some really nice long sideburns and a moustache; the latter is still with me today and my hair is actually longer.  However, I was a geologist (or at least a student) and we were tough, wore boots and jeans and wide brimmed hats (vernacular: cowboy hats).  But, I studied hard and dutifully reported events of importance to my draft board back in Kansas (like grades).  I was married (still am), was poor, drank 'three quarts for a dollar" beer and ate lots of pasta (mostly without meat).  But, all of my friends were in the same boat and we had fun.    

This war has already stretched the generation gap so wide that it threatens to pull the country apart.
--Sen. Frank Church, May 1970

1968 is hard to explain to my children.  It was one of those events, perhaps like WWII, that if you weren’t there you don’t understand.  For me it was the best of times as I was newly married, loved learning, the institution, the teachers, and the finalization of a dissertation project.  It was also the worst of times as so many young men of my age were coming home from Southeast Asia in boxes or were drastically changed persons.  Several of my friends were discharged from the Armed Forces on the West Coast and stopped at my house on their way home to the Midwest; they were welcomed with open arms as I greatly respected their contributions.  However, I must state, they were not “happy campers.”

We are not about to send American boys nine or ten thousand miles away from home to do what Asian boys ought to be doing for themselves.
--Lyndon Johnson, Oct. 1964

What brought on all of this nostalgic thinking about 1968?  Well, I had re-discovered a beautiful piece of cornwallite in my collection that came from the Mammoth Mine in the Tintic District of Utah.  In those days the Geology Department had few Friday classes as that day was reserved for field trips or research.  In addition, the Department sponsored a weekly seminar (vernacular: Lunch Club) with external speakers that was required attendance for majors and graduate students.  I was fascinated upon hearing the USGS geologists talk about Tintic and the great mining activities (see Shepard and others, 1968).  The Department also sponsored a field trip to the area although we were not allowed to venture underground.  Ten years later the USGS geologists completed a Professional Paper (#1024) on the district and I devoured that in one reading. 

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

The 1916 edition of the Eureka Reporter noted “The Tintic District lies about 85 miles due south of Salt Lake City, and on the west central slope of the Tintic Mountains, a short range which forms the connecting link between the Oquirrh mountains on the north and the Canyon range on the south, the group constituting the first of the Basin ranges to the west of the Wasatch mountains.  The mountains here rise to a height of 8,108 feet, rising and falling abruptly.  The western end of Tintic valley finds the mountain peaks 5,600 feet above sea level, while in the Goshen valley at the east they are 4,600 feet.  The regularity of the range is broken by many lateral valleys, one of which has cut well back into the range, forming a low divide above the town of Eureka, through which the D & R G railway [entered] the district.” 

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

Morris and Lovering (1979) described the general geology as “… consisting of the eroded flank of a composite volcano, which, during the Oligocene, buried a preexisting mountain range that had been carved from folded and faulted Paleozoic sedimentary rocks.  During this volcanic episode many stocks, plugs, dikes and other intrusive bodies were injected into both the sedimentary and volcanic rocks.  As the Oligocene volcanic and intrusive episode subsided, great volumes of hydrothermal solutions coursed through the rocks, chiefly among faults and fissures eventually depositing large replacement ore bodies and veins that occur almost exclusively in the sedimentary rocks underneath the hydrothermally altered lavas.”

So, several large volcanoes 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 crystalize forming the ore bodies in the limestone.

Wilson (1995) summarized the minerals (noted 175 species) of the Tintic Mining District: “…located at Eureka in Juab County [and] was discovered in 1869…Much of the production of siliceous ore in the district has been 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.  In addition, gold is locally common…”

But, as Black (2010) noted, the Tintic District has produced a variety of unusual and rare minerals “including …minerals that blend copper, silver, tellurium, arsenic, sulfur, carbonates, hydrodixes, etc. …The Centennial Eureka mine… is the type locality (where the mineral was first identified) for leisingite, frankhawthorneite, jensenite, juabite, utahite, and eurekadumpite. Other rare minerals include xocomecatlite, carmenite, adamite, duftite, and mcalpineite.”  Cornwallite is also present and is not a common mineral.

Cornwallite is an arsenate and related to such minerals as duftite (Posting May 10, 2014), carminite (Posting May 18, 2014), arsenopyrite, adamite (Posting April 23, 2012) and conichalcite (Posting December 8, 2011).  The arsenates contain the AsO₄ radical and are usually grouped together with the phosphates (PO₄ radical) and the vanadates (VO₄ radical) since the three radicals are similar in size and commonly substitute for each other (and change the mineral).  The total minerals in these three groups number in the hundreds and are second only to the silicates in total number. However, many of the minerals are rare and only a few are common (such as the phosphatic apatite minerals).

Photomicrograph of arsenic crystals, the fresh tin-white crystals and the tarnished darker crystals.  Width of specimen ~7 mm.

The arsenates contain the metallic element arsenic (atomic number 33 on the periodic table) although most mineralogists prefer to call arsenic a metalloid since it is not a true metal.  At any rate, arsenic does occur in a natural state although it is quite rare—at least today.  I wanted to actually see what crystals actually "looked like" so purchased a small specimen from a mine in Borneo, part of Malaysia.  It appears, at least to me, that most specimens of arsenic “for sale” come from this island.  Arsenic is a “tin-white” color when fresh but weathers to a dull black color.  Evidently it is almost impossible to tell arsenic from antimony (Sb) and most antimony contains some arsenic and vice versa.  In fact, the antimony mineral stibnite is sometimes associated with native arsenic (Posting April 16, 2013).

Cornwallite always has been sort of interesting to me due to its type locality, the famous Cornwall Mining District in southwestern England.  The District began to produce ore minerals, mostly tin and later copper, in perhaps 2000+ BC.  Evidently the inhabitants mined the tin and traded with/shipped to civilizations in the Mediterranean.  There the tin was added to molten copper and voila---bronze.  Cornwall also produced a variety of secondary arsenates as byproducts of the tin and copper mining.  Most mined arsenic came from arsenopyrite (FeAsS); however, a variety of other minor and quite colorful minerals also contributed: clinocase, liroconite, olivenite, chalcophyllite, and the areas namesake, cornwallite.

The Cornish miners were well regarded in the United States and many were called to the States to supply their expertise in the burgeoning area of hard- rock mining.  In reading historical records of mining districts in the western U.S. I found numerous references to the skills of these miners and they were considered the world’s greatest hard-rock miners.  Rickard (1932) stated the Cornishmen “knew better than anyone how to break rock, how to timber bad ground, and how to make the other fellow shovel it, tram it and hoist it.”

Lead mine near Shullsburg, Wisconsin.  Photo courtesy of WWW.Miningartifacts.org.

I lived in Wisconsin for several years and the Cornish miners left their mark in a number of ways.  Lead (galena) was discovered (at least by Caucasians) in the 1820s in northwestern Illinois and miners soon moved upriver into southwestern Wisconsin by the late 1820s.  By 1830  miners were working the shallow prospects in southwestern Wisconsin, and as the story goes, they did not have time to build houses and simply dug living holes next to their mine---hence the nickname “badger” was applied. By the mid-1830s Cornish miners in England were looking for new experiences and “diggins” and miners flocked to the U.S and especially to the Wisconsin/Illinois lead mines.  Wisconsin immigration and mining records indicate that perhaps 7000-8000 workers of Cornish descent lived in southwestern Wisconsin by the early 1850’s.  But, lead mining started declining and the skilled miners begin trekking to copper mines in the Upper Peninsula of Michigan and to the California gold fields.  However, these “Cousin Jacks (male Cornishmen) and Jennies” left behind a rich cultural heritage, as well as important contributions to American mining: the terms lunch bucket, miner’s candlestick and the implementation of the Cornish Pump to remove water from the mines.  I have always been partial to that culinary delight: Cornish Pasties! 

Green, globular cornwallite, Mammoth Mine, Tintic Mining District.  Width ~3.7 cm.

OK, back to cornwallite, a copper arsenate hydroxide. If the phosphate radical replaces the AsO₄, the mineral becomes pseudomalachite; however, I am uncertain if intermediate minerals are in this series from arsenate to phosphate (I have been unable to locate such).  Cornwallite is a secondary mineral found in the oxidized zones of copper sulfide deposits where the ores contain both arsenic and copper and perhaps oxidized from something like tennantite (Cu₁₂As₄S₁₃) or enargite ( Cu₃AsS₄) .  Most cornwallite occurs as botryoidal to globular crusts of microcrystalline radiating fibers.  The dominate color is essentially an emerald green.  Cornubite (Triclinic System) is a dimorph of cornwallite (monoclinic) ---same chemical formula but different crystal systems.

Cornwallite is a beautiful mineral when observed under magnification.  Viewers really cannot see tiny crystals; however, the color of the “globs” is spectacular.  The major problem with these colorful arsenates is that they are really difficult to distinguish from each other.  Collectors can assign a name but without some optical/chemical tests this assignment is often tenuous (at least for an ole paleontologist like me).  So, I listen to the words of Harold Wilson (former UK Prime Minister): I’m at my best in a messy middle-of-the-road muddle.

REFERENCES CITED

Black, D. V., 2010, the Geology of the Tintic Mining District: http://elementsunearthed.com/2010/07/13/the-geology-of-the-tintic-mining-district/

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

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. 

Morris, H.T., and Lovering, T.S. (1979), General Geology and Mines of the East Tintic Mining District, Utah and Juab Counties, Utah: USGS Professional Paper 1024.

Shepard, W.M., H.T. Morris and D.R. Cook, Geology and Ore Deposits of the East Tintic Mining District, Utah, in Ore Deposits of the United States, 1933-1967,:American Institute of Mining and Metallurgical Engineers, 1968.

Rickard, T.A., 1932, A History of American Mining: McGraw-Hill Book Company, Inc., New York.

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