Wednesday, July 1, 2015

CORNETITE: BLUE COPPER PHOSPHATE



I am a sucker when it comes to purchasing blue, red or green minerals if the price is reasonable (cheap), and especially if they are phosphates, arsenates, or vanadates.  Two thoughts here: 1) I noted in a previous blog that I purchase minerals, not for an office display nor a case at the local rock show, but to learn as much as possible about the species and then “write it up” for this blog or a club newsletter.  One of my goals in life is to continue, “till the end,” to be a life-long learner.  So, spending something in four figures would put a crimp on purchasing 200 other specimens---my learning curve would bottom out.  Strange---perhaps, but this life–long learning is a passion and helps keep me intellectually alive; and 2)  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. Many are colorful; however, most members of the group are rare and only a few are common (such as the phosphatic apatite minerals).

While rummaging around down in Tucson last February at some small out-of-the way venue I noticed something “blue” that really caught my eye.  Snagging the specimen out from under a few other boxes I became really interested: 1) the specimen was priced under $5; 2) the specimen was deaccessioned from the “Mineralogical Museum, New Mexico Bureau of Geology & Mineral Resources, New Mexico Tech.”  Labels like this on a mineral specimen are an added bonus.  I also picked up a second specimen, via mail order, from Sauktown Sales.

OK, the blue mineral is cornetite, a copper phosphate hydroxide—Cu3(PO4)(OH)3—that is relatively rare in the record.  It occurs as a secondary mineral of the oxidized zone in a few hydrothermal copper deposits.  Cornetite is not as common as the other basic copper phosphates libethenite [Cu2PO4(OH)] and pseudomalachite [Cu5(PO4)2(OH)4]---see Blog Posting January 11, 2015. I have been unable to find a reference that would lead me to understand why cornetite is such an uncommon mineral!  What are the conditions necessary for the formation of cornetite?  Another day, another question awaiting an answer!
 

Photomicrograph with bright blue equant crystals and long prismatic crystals in large specimen. Long dimension of largest cluster ~3.5 mm.


Photomicrograph of scattered crystals of cornetite.  Largest cluster is noted in close up above.


Clusters of cornetite rosettes forming a crust. Width FOV ~1.5 cm.

Cornetite is an attractive collectable mineral due to its bright blue to bluish-green color on tiny vitreous crystals.  The crystals are microscopic prismatic, some are equant, and are one to two millimeters or less in length and sometimes rounded. They often cluster together in radial aggregates or rosettes and sometimes form a crust.  They have a hardness of ~4.5 (Mohs) and range from transparent too translucent.  Crystals may be confused with azurite; however, cornetite is not a carbonate, as is azurite, and will not effervesce in hydrochloric acid (although it is soluble in cold acid).
Cornetite is an uncommon mineral and is only known from a few localities in the United States (Colorado, Arizona, New Mexico and Nevada with several questionable occurrences), Australia, Chile and a few European countries. It is best known from the Democratic Republic of Congo (Zaire), the type locality (L'Etoile du Congo Mine [Star of the Congo Mine; Kalukuluku Mine]) and the site of my specimens. The Etoile orebody lies within the copper belt that stretches from Luanshya in Zambia to Kolwezi in the Democratic Republic of Congo. Shalina Resources (2010) noted that as with many of the deposits in southern Katanga, Etoile is a stratiform copper-cobalt deposit. There is an enlarged oxide cap of about 160 ft that overlies an inclined stratiform sulfide deposit.  Although abandoned in the 1960s, it is my understanding that the mine went back on line after new owners (Shalina Resources) purchased the area in 2003.  The open pit mine processes supergene replacement minerals from the upper oxide zone but has plans to continue mining down into sulfide deposits.  Etoile is rich in cobalt (paying half the bills) and I presume they are mining spherocobaltite [CoCO3] and Heterogenite [CoO(OH)], minerals listed by MinDat.  There are a variety of copper oxides in the enriched zone included malachite [Cu2(CO3)(OH)2] and tenorite [CuO].  However, I have been unable to locate information about the minerals available for mining in the underlying sulfide zone. 

So, cornetite is another blue copper phosphate that is a nice addition to my modest collection.
REFERENCES CITED

shalinaresources.com/geology.aspx (2010)

Thursday, June 25, 2015

MISSOURI MOZARKITE, COAL & GEODES




I had the opportunity to live and work in northeastern Missouri during the early 90s.  The landscape was interesting with lots of deciduous trees and rolling hills.  The spring seasons were beautiful in that the forest was filled with blooming trees, shrubs and a variety of flowers.  The combination of flowering redbud and dogwood really livened up the landscape.  Towering above the smaller trees and shrubs were fairly large hickories and oaks.  Although almost all were second or third growth trees, occasionally a giant specimen indicated the loggers missed or ignored the individual.  I lived “in the country” and had a couple of these large specimens on my few acres---even at my age they were an enjoyment to climb, perch and contemplate life!

Northeastern Missouri is in a physiographic region termed the Dissected Till Plains (DTP).  In fact, the DTP extend south to the Missouri River (flowing west to east [Kansas City to St. Louis] through the middle of the state.  What this indicates is that the Missouri River is essentially an ice marginal stream---the great Pleistocene glaciers covered the northern half of the state but not the Ozark Plateaus south of the River.  The glacial till, composed of a variety of sediments from clay to boulders, varies in thickness (several hundred feet thick in ancient glacial valleys), and is being eroded and dissected by modern streams---hence, the rolling hills.

In some localities, a thin veneer of wind-blown loess (clay and silt size particles transported from glacial outwash plains) covers the till.  In northeastern Missouri the till usually sits on Pennsylvanian rocks composed of limestone, shale and sandstone, often of marine near shore, deltaic or swamp environments.  In fact, the area around Kirksville (my home for seven years) had a robust coal mining economy a century ago.  The small town of Novinger, about 10 miles west of Kirksville, was the center of mining activity and the Kirksville Daily Express (September 6, 2014) noted the “coal mines started making their way to Novinger during the late 1800s.  From 1880 to 1966 the city of Novinger was home to 57 coal mines in Adair County, which was labeled as the third largest producer of coal in the state in 1912 in a report done by the Missouri Bureau of Labor Statistics in 1914. Novinger was also the home to the Billy Creek Coal mine, the last deep-shaft mine in the state before it closed in January 1966.” Today the only references to the mines are scars of the Pennsylvanian rocks visible in openings of the till; at least that is all I could locate.  Some of the local population noted that several tunnels existed under the city---fact or fiction, I do not know.  
 
Postcard  of buildings at the Rombauer Coal Mine near Novinger.  Courtesy of: Novinger Planning Progress © 2003.
The area surrounding Kirksville was not exactly a hotbed of mineral and fossil collecting!  I sorted through some of the “gravel pits” looking for chalcedony and/or jasper.  Once I looked for rumored Lake Superior Agates  in a gravel pit along the Mississippi River two counties to the east—no luck.  The best (in fact great) mineral collecting was looking for the famed Keokuk Geodes a couple of counties east and one north around the small city of Keokuk, Iowa, across the River.  However, the Mississippian Warsaw and Keokuk formations also crop out on the Missouri side and offer the geodes.  These Mississippian rocks are older than the Pennsylvanian rocks exposed near Kirksville.
 
Keokuk-type Geode (width ~4.5 cm.) collected near Hamilton, Illinois.  Note secondary dolomite crystals on quartz lining.
Other than the Keokuk Geodes Missouri’s better known minerals probably are those associated with the Tri-State (Missouri, Kansas, Oklahoma) Lead and Zinc District (see posting 7/21/14) and the Lead Belt/Viburnum Trend in the southeastern part of the state (see details on 6/28/14 posting).
However, in visiting with lapidaries most could care less about the calcite, galena, etc. but mention Mozarkite and their eyes light up!  As a side note, I never understood something here.  If a locality where colonies of bees are housed are called apiaries and bee workers (human) are apiarists why are people working with polishing minerals not called lapidarists?

Mozarkite (MO:Missouri; ZARK:Ozarks;ITE:mineral) is not an officially recognized mineral but is a form of cryptocrystalline quartz.  I have seen it referred to as a variety of chert or flint or chalcedony.  Whatever your choice, the specimens are a swirling array of colors (often pastel in shade) notably purple, blue, brown, yellow, red, orange, salmon, white, and more and due to impurities such as iron, copper, manganese, nickel, etc.  Since it has a hardness of ~7.5 specimens take a high polish and are fashioned into a variety of cabochons and free forms for wire wrapping or setting in pendants.
  
Polished mozarkite nodule. Width ~4.0 cm.

Polished mozarkite nodule. Width ~3.0 cm.

According to Missouri lapidaries mozarkite is unique to the state and is only found in a few areas south of the Missouri River and west of the Lake of the Ozarks, most notably around the small town of Lincoln in Benign County.  It occurs in nodules (up to cobble and boulder size) weathering from the Cotter Dolomite of Ordovician age.  On a road trip when living in Missouri I stopped and searched a few road cuts and roadside ditches and gathered up a few smaller nodules.  Unfortunately, those became a causality of my several moves across the country.  However, I still have in my collection a couple of smaller pieces (purchased) that are nicely polished. I can understand why lapidaries are enamored with mozarkite.  In fact, the State Legislature also was enamored since in 1967 Senate Bill 216 designated mozarkite as the official Missouri State Rock.  I would have preferred state mineral; however, that slot was occupied by galena!