Thursday, January 21, 2021

LOAFING AROUND WITH ALBITE, SCHORL, AND MONAZITE

 
Public Domain: artist unknown.

The other morning I was just sort of loafing around, enjoying my coffee, thinking about the day, when I spotted a rock over in the corner mostly hidden under some junk.  Yea, I kind of remember that piece—came with a “box of rocks” and lacked a label.  I was always going to look at it “someday” and try to make an ID.  Well, this lazy morning, somewhere around 300 in the pandemic self-quarantine, would be a good opportunity to take a peek.  Besides the lack of a label, I had tossed it aside since the softball size of the specimen was much larger than I usually tackle since it exceeds the operating distance of my binocular scope. But I grabbed my 10 power loupe and wow, this was an interesting rock, but it still lacked a locality label.  However, it had a very distinct look, almost like a poorly cemented conglomerate with large albite and schorl crystals and something orange and small---that should help with the “picture ID” on MinDat.org. Time to refill the coffee mug and get started.

After spending time on the internet, and perusing mineral books and articles, I have concluded my rock came from Portugal No. 2 quarry, Malpartida e Vale de Coelha, Almeida, Guarda, Portugal. Now I know very little (not much at all) about the geology of Portugal and the best I could find is from MinDat.org: Granite quarry with several pegmatite layers rich in pockets. Adjoining pockets may show quite a different mineralization. there are other granite quarries in the vicinity, presumably with similar minerals. 19 valid minerals known.

The mystery rock with a mass of albite crystals while the black crystals are schorl.  Width of specimen ~13 cm.


 Partial schorl crystal; length ~2.5 cm. 
White, pearly luster, albite (sodium-rich feldspar) with scattered, terminated schorl crystals.

Note the tabular, stacked parallel crystals of albite at <-----.

Not all schorl crystals are large--note the tiny needle-like crystal.  

A base geologic map indicates that northern Portugal is a granitic terrain that evidently is associated with the Variscan Orogeny, a Late Paleozoic continental collision between Euramerica (Laurussia) and Gondwana to form the supercontinent of Pangaea.  There appears to be tens of granite quarries scattered across the area and this granite terrain contains the Central Iberian Pegmatite Belt. Ages of the various pegmatites are close to those that characterize the granites, ~300 Ma (evolution of older granites) and ~290 Ma (later granites). The parental plutonites are syn-tectonic two-mica granites and late to post-tectonic biotite granites (Dias and others, 2013).

And that is about my sum knowledge of Portuguese geology except that the Douro River flows through the granite and the associated soils produce the famous port grapes for the wines!

In looking closely at the rock, I discovered a mass of albite (plagioclase feldspar; usually white to gray) with a variety of different size schorl crystals (most common member of the Tourmaline Group; black in color).  But the most interesting crystal half concealed in the albite mass was a partial, large (~2.1 cm) crystal of what I believe is monazite, a reddish-brown phosphate mineral that contains rare-earth elements (REE/Ce/La/Nd/Sm/Gd)(PO4). According to MinDat.org the Portugal #2 Quarry does not list a dominant monazite REE so identifies it as monazite ?

A large (width ~2.1 cm) monazite crystal stuck in the mass of white albite crystal.  Note the smaller, transparent, golden, tabular crystal of monazite "on top of" the larger crystal.

The albite mass also contains a number of small (1-2 mm) orange to orange-brown crystals that I first thought were spessartine garnets since they were common in photos supplied by MinDat.org.  However, something was wrong since the crystals seemed not to resemble typical garnet crystals of any kind.  These crystals were flattened, thin, and wedge shaped.  In addition, there are consolidated masses of these colorful crystals.  So, readers can examine my photos and perhaps come to their own conclusions—did I pick the correct collecting locality?  Are these crystals correctly identified as monazite ?  At any rate, I had an interesting time with the mysterious rock!







The above photomicrographs are ~1.0 cm. width FOV and show the brown to orange brown small crystals on monazite ?  encased in the albite mass.

I remain uncertain about the "crud" often covering schorl.

I believe the white material at the end of the pointer is ?aragonite.

REFERENCES CITED 

 Dias, P.A., B. Pereira, J. Azevedo, J. Oliveira, Leal Gomes, and J. Carvalho, 2013, Pegmatite Productive Terrains in the Variscan Granite Hosts From Northern and Central Portugal: 23rd International Mining Congress & Exhibition of Turkey • 16-19 April 2013 ANTALYA [https://repositorium.sdum.uminho.pt/bitstream/1822/30028/1/IMCET2013_Dias_et%20al.pdf]

 

 Give me a mystery, just a plain and simple one, a mystery which is diffidence and silence, a slim little bare-foot mystery: give me a mystery, just one.              Yevgeny Yevtushenko

Saturday, January 16, 2021

PAPAGOITE AND AJOITE FROM AJO, AZ

Like many people I am fighting pandemic fatigue as it seems I am pretty much confined to my home, and to my "office" in the basement.  The Covid pandemic has seemed to take away many joys of our lives and the daily news and numbers are really discouraging.  But then I tell myself--suck it up, you are well and safe and have food and shelter.  And I am never too old to set a new goal in life, or dream about a new writing project, and as long as the earth continues revolving then tomorrow is another day.  And when I awake in the morning I am reminded that yesterday ended last night, today is a new day, and the coffee will taste wonderful.

 See the source image

Public Domain. Autor/artist unknown but thanks.

The major copper ores in Arizona have been/are found in very low- grade ore called porphyry copper deposits where the disseminated copper makes up less than 1% of the total ore.  Anthony and others (1995) noted that these ore deposits are generally found in the Basin and Range Physiographic Province, “are always associated with an intrusive calc-alkalic porphyritic rock [distinctive difference in grain sizes]…typically quartz monzonite [intrusive igneous rock with equal amounts of orthoclase and plagioclase and 5-20% quartz], tonalite [intrusive igneous rock with major plagioclase and less than 10% orthoclase with more than 20% quartz], or granodiorite [intrusive igneous rock with major plagioclase, some orthoclase and greater than 20% quartz]…ranging in age from late Mesozoic through middle Tertiary…The major primary [hypogene] ore minerals [are] chalcopyrite (CuFeS2), some bornite (Cu5FeS4)  [while] pyrite is typically the most abundant sulfide.”  In some porphyry deposits, weathering of the upper exposed surfaces allowed the formation of sulfuric acid and iron and copper sulfates [especially from the pyrite] and percolated downward where secondary ore sulfides were deposited, especially chalcocite (Cu2S), in the supergene [layer around the water table].  The collectable secondary minerals of porphyry copper deposits such as azurite, malachite, cuprite, chrysocolla and others were deposited in the uppermost oxidized zone [above the supergene] or in deposits peripheral to the major porphyry deposits. 

Cuprite, copper oxide, from the oxide zone at Ajo. Cuprite is an ore of copper. Width FOV ~1.5 cm.

The New Cornelia Mine is near the town of Ajo in southwestern Arizona, and in fact, Ajo was a company town for the miners and is the name typically associated with the mining district.
  The New Cornelia is a large porphyry copper deposit and copper was mined in one of those huge open pit mines about 7600 feet across and over 1100 feet deep.  I find it amazing that in the initial mining “boom” in the mid-1800s, the miners needed to ship the New Cornelia ore clear to Swansea, Wales, for processing!  I have not been able to locate the exact route the ore took on its journeys—but perhaps it was hauled by horses/mules to the Sea of Cortez and then by ship to the United Kingdom.  As one might suspect, the profit margin of this low-grade ore was nonexistent.  In fact, it was not until around 1915 that a smelter was constructed nearby, and miners begin to excavate the copper carbonates, for example azurite and malachite, in the upper oxidized zone.

Azurite is typically found as...prismatic crystals of a deep azure blue color with splendent vitreous faces (Mindat.org).  Termination of stubby very deep blue azurite from the upper oxidized zone of the New Cornelia Mine. Width of crystal ~1.1 cm.

During this process of mining with steam shovels, the New Cornelia became the first, large open pit mine in Arizona.  But like most porphyry copper deposits, the easily mined copper carbonates became exhausted and miners then began to attack the underlying hypogene ore (chalcopyrite and bornite) by the mid- 1920s.  Unlike many porphyry copper deposits, the New Cornelia did not contain a copper enriched supergene layer.  Mining continued until about 1983 when “union problems” and low commodity prices forced the closure.  New Cornelia produced over 6.3 billion pounds of copper (and some gold and silver) during its life (Arizona Department of Mines and Mineral Resources, 2008).

MinDat lists 83 valid minerals known from the New Cornelia including two, ajoite (K,Na)Cu7AlSi9O24(OH)6-3H2O) and papagoite (CaCu[H3AlSi2O9]), where the mine is the Type Locality.  Both of these rare minerals were/are collected from the upper oxidized zone and my specimen of ajoite was described in a previous posting. Recently I acquired a very small specimen of papagoite and wish to add it to my listing of minerals.

This is my lonely specimen of blue papagoite attached to matrix.  The width (long right-left axis) is ~1.0 mm.
 
Papagoite is less common than ajoite but shares its characteristics of very small crystals.  While ajoite is mostly blue green in color papagoite trends toward blue.  The most sought-after specimens of papagoite are the included quartz crystals of  Limpopo, Vhembre District, South Africa. Papagoite is harder (~5.5 Mohs) than ajoite, transparent to translucent, and brittle with a vitreous luster. Most of the time the Ajo crystals are indistinguishable with the naked eye.  The South African, included-quartz crystals display radiating aggregates.  The veinlets in the Ajo granodiorite porphyry are quite small and narrow. The specimen I acquired is an aggregate of microscope crystals without any distinguishing characteristic except its collecting location.

Ajoite is the mass of blue-green to transparent mat of crystals.
The Ajo ajoite, is also blue-green copper silicates oxidized from the copper rich hypogene minerals.  Arizona specimens are usually sprays of bladed prismatic crystals (elongated along the C Axis), small ~3-5 mm), and flattened.  The crystals on my specimen are the flattened sprays that almost appear to be mats.  However, the most sought after ajoite specimens are (again) from Limpopo, Vhembre District South Africa where gemmy quartz crystals are included. Ajoite crystals have a vitreous luster, are transparent in individuals, a greenish-white streak, and a hardness of ~3.5 (Mohs). 

REFERENCES CITED

Anthony, J.W., S.A. Williams, R.A. Bideaux and R.W. Grant, 1995, Mineralogy of Arizona, 3rd Edition: The University of Arizona Press, Tucson. 

Arizona Dept. of Mines and Mineral Resources, 2008: Arizona's Metallic Resources Trends and Opportunities - 2008


Sunday, January 10, 2021

COLORADOITE, STEGOSAURUS, AND THE COMPROMISE OF 1877 + SILVER DOLLARS

 

In 1961 Edwin B. Eckel of the USGS, after 30 years of work, authored Bulletin 1114, Minerals of Colorado: A 100 Year Record.  The Bulletin was a major contribution to understanding mineral resources of Colorado and was popular with both amateur rockhounds and professional geologists.  On pages 6-7 Eckel noted that “during the past 100 years Colorado has given 42, new, or type, minerals to the science of mineralogy. [In addition, there are] 22 Colorado minerals that were first described as new but whose validity as species has since been discredited.”

The earliest record in Eckel’s Type list is from 1874 when Genth (1874) described schirmerite, a silver-lead-bismuth sulfide, from the Geneva District located about two miles southeast of the mining community of Montezuma (located a few miles east of the Keystone Ski Resort). The next record is 1877 when Genth described the mercury telluride mineral, coloradoite, from Boulder County.

Ah, 1877 was an interesting year and earlier this winter I had been reading about the Compromise of 1877 ( as a history buff bored in the pandemic I locate and read about all sorts of trivial “happenings”).  However, suddenly the Compromise was seemingly made relevant due to the election of 2020, at least wrongly relevant to Senator Ted Cruz (R-TX).   In the election of 1876 Samuel Tilden (D-NY) won the popular vote for president by ~250, 000 votes over Rutherford B. Hays (R-OH) and accumulated 184 votes in the electoral college.  Unfortunately for Tilden, 185 electoral votes were needed for victory (Hays garnered 165 electoral votes).  Republicans claimed voter fraud (nothing new in 2020) and Louisiana, South Carolina, and Florida, states still saddled with Reconstruction-era governments in power, sent in two conflicting sets of electoral votes---what to do?  Well, Congress formed a Commission and was in discussion when Republican minions of Hayes secretly negotiated a “compromise” with southern Democrats of the three contested states to throw their support, and 20 electoral votes, to Hayes (originally the Democrats had supported Tilden) allowing him to reach the magic number of 185.  In return for their support, Hayes essentially gave away the store by withdrawing all Federal troops from the southern states and ending Reconstruction.  In doing so he abandoned the freed slaves and ushered in the ear of Jim Crow laws.  In short order, state governments in the southern states stopped enforcing the 14th Amendment (Black Citizenship), the 15th (right to vote), and the Civil Rights Act of 1866.  The U.S. is still trying to come to terms with the Compromise of 1877.  Meanwhile in Colorado, Leadville was booming and was “founded” by mine owners Horace Tabor and August Meyer in 1877.  In Morrison, Colorado, on the eastern front of the Rockies, one of the world’s best-known dinosaurs, Stegosaurus, was discovered in the Jurassic Morrison Formation.  In August 1876 Colorado had become the 38th state and so the November presidential election was their first--but not really for the general population!  In those days of old, the Colorado General Assembly picked the three presidential electors and awarded their three votes to Rutherford B. Hayes. This was the final time in U.S history that any state awarded electoral votes without the candidate winning the popular vote.  So, in a way, Colorado had a giant voice in electing Hayes for if our statehood had come four or more months later those three electoral votes would not have been available.  I suppose Tilden would have become President and our country would have changed.  One can only speculate “how.” As for Senator Cruz, he needed to study history.  The 1877 Commission was formed since the electoral vote had not been formally certified by all states—at least there were conflicting sets of “certified” electors submitted to Congress.  In 2020, all electoral votes submitted to Congress had been certified by every state—end of debate.  Finis.

Eckel’s Bulletin was such a popular read that various members of the Friends of Mineralogy, Colorado Chapter, and the Denver Museum of Natural History (now Nature and Science), spent 20 years updating the book and published, in 1997, a 665-page tome entitled Minerals of Colorado.  Eckel provided information on 445 Colorado minerals while the revision described 774 Colorado minerals.  While Eckel described 42 Tyle Minerals from Colorado I counted 66 Types listed in the revised book.  I do not have appropriate information to speculate on new Types that Colorado may have produced since 1997.

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) (a tellurite) as in the uncommon mineral tellurite, TeO2 (described May 30, 2020), or with a 6+ oxidation state (VI) (a tellurate) as in jensenite, Cu3TeO6-2H2O.   The telluride anion with a charge of 2- often combines with gold and silver cations in the minerals calaverite (AuTe2) and sylvanite (AuAgTe4); both minerals form major gold ores at Cripple Creek, Colorado (sylvanite described October 25, 2020). Coloradoite is an uncommon telluride where tellurium (2- oxidation state) combines with mercury (2+ oxidation state) and the result is HgTe.

Genth (1877) named coloradoite for the State as he described the Type Specimens from the Smuggler, Keystone, and Mountain Lion Mines in gold mining districts west and northwest of Boulder.  However, in Colorado the largest concentrations (and I use that term loosely) seem to be in the San Juan Mountains. My small specimen came from the Bessie G Mine in the La Plata Mountains, a subrange of the San Juans located northwest of Durango.  As with many tellurium minerals, I remain somewhat confused (easy for me) to fully understand coloradoite.  Most specimens are exceedingly small (millimeters) in size and are intermixed with other tellurium, gold, and silver minerals.  I certainly do not have the determinative mineralogical skills, nor the electronic gizmos, to help with sorting out the different minerals. But, as T.S. Elliot noted, if you aren't in over your head, how do you know how tall you are?



A mixture of telluride minerals, silver shiny plus black, with gold in a quartz matrix from the Bessie G Mine.  The black mineral is probably coloradite while the silver my be coloradite or another telluride.  There is also free gold in the quartz noted in middle photomicrograph.  The length <---> of the telluride  exposure is ~1.6 mm.

Vogel and Gonzales (2014) did note that the mines in the La Platas are associated with several laccolithic complexes that are Laramide in age, ~70 Ma. The mining district is well known for vein and replacement epithermal (shallow thermal deposits associated with hot fluids) gold-silver deposits that form in association with telluride minerals.  Besides coloradoite, the Bessie G has produced the tellurium minerals alaite, calaverite, hessite, krennerite, magnolite, petzite, sylvanite, and st├╝tzite. Coloradoite is soft (~2.5 Mohs), has a metallic luster, is black to gray black in color, has a black streak. Specimens are usually granular to massive with crystals indistinguishable.

REFERENCES CITED

Genth, F.A. (1877) Stated meeting, October 20th, 1876. Proceedings of the American Philosophical Society: 16: 287-289.

Vogel, C. (2014, October). Insight into the Origin of Gold at the Bessie G Mine, La Plata Mining District, Southwestern Colorado. In 2014 GSA Annual Meeting in Vancouver, British Columbia.

As another little bit of trivia, Colorado mining interests probably wished they could has rescinded their electoral votes for Hayes. During Grant's term in 1873, Congress removed the use of silver dollars as authorized coins (Coinage Act of 1873).  Of course this action aggravated, well actually more than aggravation, silver miners and the mining companies. They certainly wanted to mine and sell more silver!  Enter the Bland-Allison Act of 1878 that required the U.S. Government to purchase between two million and four million dollars of silver each month from mines in the western states and then mint the bullion into spendable silver dollars.  Well, Hayes vetoed the the bill (another aggravation) but his veto was overridden and the Act became law.  That really was not much silver and the western miners continued to complain until the Silver Purchase Act of 1890 (Sherman Silver Purchase Act of 1890) required the Government to purchase an additional 4.5 million ounces of silver each month.  Sounds good for the mining companies but not so good for the Government.  This monthly purchase was financed by the special issue of Treasury Notes that could be purchased and then redeemed for either gold or silver--do you see a big problem brewing?  The silver currency was vastly overvalued and investors purchased silver and traded it for the undervalued gold and then sold the gold on the commodity market for big profits.  Finally the Treasury essentially ran out of gold and President Grover Cleveland got the Act repealed in 1893.  Sounds like a good deal to me--the price of silver in 1892-1893 was between $.60-.70 per ounce while gold ranged between $18-19. Ain't some trivia fascinating?  A good stress reducer!  

 

JANUARY 6, 2021: A DAY OF INFAMY

Sometimes the best thing you can do is not think. Not obsess. Just breathe and have faith that all will work out for the best.

Karen Salmansohn