MINERALS OF THE BRIDING ESTATE SALE: PART II

 

As noted in previous postings Rebecca Nohe Estate Sales recently dispersed the rock and mineral collection of longtime Colorado Springs Mineralogical Society Member Laurann Briding.  The sale attracted a large number of buyers wearing masks who were admitted via reservation (due to Covid-19 pandemic).  I was in the second group on Friday and came home with a few interesting specimens.  The narrative that follows is a continuation from Part I and starts with fluorite and calcite from the Illinois-Kentucky Fluorspar  District.

Honey-yellow fluorite, white sharply point crystals of calcite, translucent almost colorless, large calcite crystals, and colorless fluorite at top. Width FOV ~4.7 cm.

Two generations of calcite crystals scattered on the fluorite crystals.  Width FOV ~1.4 cm.

This is an interesting situation.  The larger transparent calcite crystal is covered with a later generation of slender, prismatic, snow-white calcite crystals.  Width FOV ~1.4 cm.

A second generation of clear cubic fluorite crystals.  The top border mater is synthetic material that was glued to, and held the specimen.  Width FOV ~1.4 cm.

 There are a few large, translucent "first generation" calcite crystals.  Width FOV ~ 1.7 cm.

The flat held a nice fluorite with calcite that has a small old-looking label stating it came from Cave-in-Rock, Illinois.  This, of course refers to the famous Illinois-Kentucky Fluorspar Area with the most famous mine being (probably) the Minerva #1.  Most specimens that simply say Hardin County, Illinois, or even just Illinois, are routinely assigned to the Minerva #1 (Ozark-Mahoning No. 1 Mine).  There certainly are rockhounds and mineralogists who can assign the specimens to specific mines; however, that is above my pay grade.  I have several specimens from the Area picked up on a field trip back in the 1960s, but this specimen was included in the flat and actually is pretty attractive.

The fluorite (CaF₂) in the specimen is composed of interlocking washed-out, honey-yellow cubes (with one small purple cube) along with a second generation of much smaller clear cubes.  Scattered around on the cubes are what appears to be three or more generations of calcite crystals.  The largest are clouded, poorly formed, colorless crystals with a matte luster that I first thought were witherite.  However, they effervesced rapidly in dilute HCL and so I called them calcite.  A second generation consists of long, prismatic, sharply terminated, colorless to white crystals some of which are encased, partially or completely, within the fluorite.  There appears to be a later generation of a snow-white, slender long crystals covering these original prismatic crystals.  Finally, there are clusters of very tiny, prismatic, colorless, transparent calcite crystals scattered around.  Quite a selection.

The colors of fluorite in the District vary considerably but perhaps it best known for purples and blues with color caused by various elements substituting for some of the calcium in the chemical composition. The cubic fluorite crystals have perfect cleavage and will produce a nice octahedron.  Tourist stores across the nation sell these cleaved specimens by the thousands.

Although we have fluorite here in Colorado associated with pegmatites, the Illinois-Kentucky District fluorite was deposited in fractures and faults associated with fairly flat lying Mississippian Age limestones (~330 Ma).  Low temperature hydrothermal brines, of later age (~150-250 Ma), then migrated into the voids while also partially dissolving some of the wall rock before depositing the fluorite.  The District seems related to the Mississippi Valley Type mineral deposits that produced the lead-zinc districts of Missouri, Wisconsin, and other states in the Midwest.  The question of the day is did the brines originate locally around hidden igneous intrusions, or did they migrate from the southern U.S. (today’s geography) that was tectonically active due to plate collisions?

The Mexican State of Zacatecas is in the north central part of the country and is known for the tremendous abundance of minerals and especially silver. MineraliA (2011) noted that “today the state produces 60% of the national product of silver, placing it as the second largest producer in the world. The soil is riddled with veins of silver, gold, mercury, iron, zinc, lead, bismuth, antimony, salt, copper, quartz, kaolin, onyx, calcite, cadmium, and wollastonite.

One of the great mining towns in Zacatecas is Concepcion Del Oro. Iron, lead, copper, zinc, silver, and gold have been mined since at least the mid-1500s and the production of silver, gold and copper continue today. The mines around the town are not well known for pyrite; however, a pyrite specimen was in the mixed flat and so it came home with me.  I wanted to check it out since I am not into collecting pyrite due to possible “pyrite disease” and the release of corrosive sulfuric acid and harmful sulfur dioxide gas.

Above three photomicrographs show pyrite replacing pyrrhotite.  The middle and upper photos show crude hexagonal shape of original pyrrhotite.  Width FOV ~1.2 cm.

In examining the specimen under a scope, I decided “something was kooky” with the way the numerous pyrite crystals were displayed.  The 5 x 7 cm. specimen is covered with small, gemmy, terminated quartz crystals with (up to ~6 x 11 mm) projections of interlocking pyrite crystals (actually the crystals look glued together).  It was confusing.  In searching the photo gallery on MinDat (Concepción del Oro Municipality, Zacatecas, Mexico) I did notice an interesting specimen posted by Dan Winder: “Nice pseudomorph showing granular pyrite that has replaced elongated hexagonal crystals (or stacks) of pyrrhotite. The tallest of these is 5 cm in length and looks like a calcite.”  Now these pseudomorphs certainly looked like the original mineral was calcite but what about pyrrhotite?  So off I go to a browser and type in “pyrite after pyrrhotite.”  Bingo, serendipity again. Dan Weinrich has a nice specimen of “Sparkling pyrite replacing previous pseudo-hexagonal crystals of pyrrhotite” collected from Romania, and others from Russia.  Keep looking. Luis Burillo Minerales has a number of specimens of the same; however, they were collected in Kosovo.  When all else fails, try EBAY! For $160 one may purchase a single clump of “Pyrite after Pyrrhotite, Noche Buena Mine, Zacatecas, Mexico.”  That got me closer although the mine is in a different Zacatecas municipality than Concepcion Del Oro; however, it is close. The Mine also happens to be one of the largest silver mines in the world with reserves of about 1 million oz of gold and 32.4 million oz of silver.

Spray of quartz crystals mixed in with pyrite.  Width FOV ~9 mm.

So, an interesting way to solve a small problem of probable interest only to an ole rockhound like me. The replacement of pyrrhotite (Fe_1-xS where x=0-0.125) to pyrite (FeS₂) seems to involve dissolution and then replacement with perhaps an intermediate formation of marcasite thrown in (see Qian and others, 2011) for a more complete explanation.

Pavement of hematite and goethite included quartz crystals.  Width FOV ~7 cm. 

Photomicrograph of a section of above specimen.  Width FOV ~8 mm.

And finally, at least for this round, the flat contained a sparkly group of brown to brownish-red quartz crystals. Closer examination shows the crystals are gemmy, terminated or double terminated, with the color imparted by the iron minerals goethite and/or hematite.  The specimen is not anything that I would pick up on an individual basis but, it was in the flat. The specimen was collected from Indian Mountain, Alabama, a location well known for producing phosphate minerals (see Posting Dec. 8, 2017).  However, close examination did not produce visible phosphates.  MinDat had single photo of included quartz from the locality; otherwise I am shy of information except that an old looking, handwritten label stated it was collected by one Preston Watts.

REFERENCES CITED

Gujie Fang Xia, Joël Brugger, William M. Skinner, Jiafang Bei, Guorong Chen, and Allan Pring, 2011, Replacement of pyrrhotite by pyrite and marcasite under hydrothermal conditions up to 220 °C: An experimental study of reaction textures and mechanisms: American Mineralogist, vol. 96, no. 11-12.

MineraliA, 2011, Minerals of Mexico: Oaxaca, Mexico.

Morgan, Helen, Greg Arehart, Naomi Oreskes and Half Zantop, 2014, Origin of epithermal Ag–Au–Cu–Pb–Zn mineralization in Guanajuato, Mexico: Mineralium Deposita, vol. 49.

MINERALS FROM THE BRIDING ESTATE SALE: PART I

 

The Colorado Springs Mineralogical Society lost a long-time member, Laurann Briding, in June 2020. Laurann was an active rockhound and had a large collection of both purchased and personally dug specimen.  Recently the family had the rock/mineral estate appraised by local dealer Leonard Himes and material was then turned over to Rebecca Nohe Estate Sales for disbursement on August 7-9.  Most of the material was sold by flats ranging in price from $5 to $1000 and hundreds of micromounts were available for a buck per piece.  There were also several individual cabinet specimens highlighted by a $5000 rhodochrosite from the famous Sweet Home Mine near Alma, Colorado.  Perhaps the most interesting item in the sale was a brass microscope owned by the CSMS founder and Honorary President for Life, Lazard Cahn.  That was a real find and I was hoping that a benefactor would purchase the scope and turn it over to a museum.

A brass microscope once owned by Lazard Cahn, the Honorary President for Life of the Colorado Springs Mineralogical Society.

 

 Lazard Cahn, ~1930.  Photo © courtesy of the Digital Collections at the Pikes Peak Library District.

The Sweet Home Mine rhodocrosite sold on Saturday morning for the asking price, $5000.  Notice the reflecting mirror in the back of the showcase.

A large selection of micromounts were available and a few are shown above. I was able to pick up a couple of micro flats on a return visit Sunday noon.

 Specimens and jewelry were tastefully displayed by Rebecca.

Due to Covid-19, I was hesitant to head out into a public area since I have pretty much self-quarantined at home since late March.  But, access to the show room was limited and by appointment only (30 minutes only) and masks were required. So off I went to check out the goodies.  As noted in my last posting, my best purchase was a nice specimen of the hydrated zinc arsenate legrandite [Zn₂(AsO₄)(OH)-(H₂O)], a very collectable mineral due to its color and rarity. But I did purchase a few other minerals with good specimens scattered in the flats.

When rockhounds think of collectable amethyst the concretions from Brazil pop into their mind.  Ask them about amethyst from Mexico and the gemmy quartz crystals from Vera Cruz are probably in their collection.  However, amethyst from the Guanajuato silver mines are probably not familiar to most rockhounds.  And speaking of silver, the Guanajuato mining district is one of the most prolific and best-known silver districts in the world. Silver was discovered in 1548 and estimates of historic production range from 700 million to 1.5 billion oz of silver, as well as 4.0 million to 7.0 million oz of gold. Guanajuato was a major center of a Spanish colonial mining boom; in-fact at one point, the La Valenciana mine to the north of the city accounted for up to two third of the worlds silver production. Within 20 miles of Guanajuato’s downtown there are at least eight major metal mines either in production, in development or recently closed, as well as a flurry of exploration activity.  To the non rockhounds, Guanajuato may be best known as the home of painter Diego Rivera, the husband of painter and political activist Frida Kahlo.

The Guanajuato mines are classified as “epithermal vein deposits” where a variety of minerals are located in veins that are probably the result of previous fractures and cracks in the host rock.  The hydrothermal brines, especially sodium-calcium-chloride brines, are effective solvents and are able to dissolve the primary sulfide ores and circulate through the host rocks.  As these brines begin to cool, usually at shallow depths, deposition of minerals take place and often these veins of minerals are quite rich.  In fact, epithermal gold deposits are some of the richest gold deposits in the world. At Guanajuato mineralization consists dominantly of silver sulfides and sulfosalts (a metal + semi-metal + sulfur), base metal sulfides (metal + sulfur) mostly chalcopyrite, galena, sphalerite, and pyrite, and electrum (alloy of silver and gold). Gangue minerals (the waste rock) are generally quartz and calcite; the host rocks (holding the minerals) are Mesozoic sedimentary and intrusive igneous rocks and Tertiary volcanic rocks (Morgan and others, 2014).

 Amethyst base with showy, snow white, rosettes of micro calcite crystals. Width FOV ~4.7 cm.

 I did not come home with a piece of silver or gold but did acquire a showy purple and white specimen with a base of gemmy terminated crystals of amethyst covered with rosettes of tiny snow-white crystals of calcite.  I could not locate information on the collector although the label appears to have some age and originally sold for $6.

Another specimen in the acquired mixed flat is a really nifty piece that has a core and base of white, well formed, dolomite crystals with a partial crust of surficial brownish-black to reddish-brown, botryoidal (individual botryoids ~4 mm) goethite.  In cross-sectional view the botryoids are composed of radiating (from the center) long prismatic crystals that have a metallic luster and a steel-gray color.  There are also tuffs or sprays of steel-gray or orange acicular goethite “sticking up” between some of the botryoids.   A second round of goethite consists of tiny (less than 1 mm) black “balls” scattered randomly across exposed dolomite crystals.  There are also: 1) numerous well-formed pyrite crystals mixed in with the micro balls; 2) a single large calcite crystal; 3) a few splotches of chalcopyrite; and 4) a hunk of massive, red hematite. All-in-all, it is an attractive specimen.

A base of white dolomite crystals with scattered micro balls of black goethite, larger black botryoidal goethite along top of specimen, scattered "clumps of pyrite, especially right, and a single large calcite crystal. Length of specimen ~ 9 cm.

Reverse of above specimen.  Note the bright red, massive hematite and the black botryoidal goethite.

Scattering of micro balls of goethite on dolomite crystals with scattered small pyrite crystals.  Width FOV ~1.7 cm.

A grouping of botryoidal goethite with hematite above and calcite and pyrite crystals.  Width FOV ~1.7 cm.

Massive hematite with micro cubes of pyrite.  Note sprays of goethite in lower right. Width FOV ~1.7 cm.

Cross sectional view of the large goethite botryoids showing acicular crystals. Width FOV ~1cm.

Sprays of gold/orange/black sprays of goethite with some nice pyrite crystals.  Width FOV ~7 mm.

The specimen came from Wawa, Ontario, Canada, a town/township/area located near Lake Superior north of Sault Ste Maria and situated in a rugged sparsely populated area. Gold and iron mines and prospects dot the area and today there seems to be a mini gold rush in progress.  The kimberlites in the area have produced diamonds and they also attract prospectors.  As best I can determine the bedrock is Archean (old Precambrian.

The specimen has an old typed label from Wallings Collector, Westbury, L.I., NY. The address seems to indicate pre-Zip Code days, so it evidently was collected before 1963.

In order to keep the file size reasonable, I have split information about minerals of the estate sale into several manageable sections. There is more coming and the previous post highlighted the zinc arsenate legrandite.