Monday, January 20, 2020

DENVER SHOW: DIOPTASE BEST $2 MINERAL




On November 24 I reported on the Denver Area Mineral Dealers fall 2019 Gem and Mineral Show held at the Jefferson County Fairgrounds on November 15-17.  I picked up some nifty minerals (see the Post) but thought I ought to mention the Best $2 Mineral Added To My Collection!  In fact, I thought it was a real find—a gemmy green cluster of dioptase crystals, a hydrated copper silicate [CuSiO3-H2O]. 

A cluster of gemmy green dioptase crystals.  Width of specimen ~3 cm.
The crystals are vitreous, emerald green in color and have a hardness of around 5.0 (Mohs) with a green streak.  Crystals are quite brittle, easily cleave, are fragile, and usually have a conchoidal to uneven fracture when broken (not along the cleavage planes).  Crystals are translucent to transparent, belong to the Trigonal Crystal System, and generally are 6-sided (hexagonal) with a rhombohedral termination.  It appears to me that once rockhounds see the emerald green variety of dioptase crystals, the sight will appear in their mind forever! 


Dioptase crystals.  Width FOV ~1.8 cm.


Drawing of dioptase, modified rhombohedral crystal.  Courtesy of smorf.nl with original from Goldschmidt, Atlas de Krystallformen, 1913-1923.

Nice modified rhombohedral crystals of dioptase (Trigonal Crystal System).  Width FOV ~ 4 mm.

Drawing of dioptase, modified rhombohedral crystal.  Courtesy of smorf.nl with original from Goldschmidt, Atlas de Krystallformen, 1913-1923.

The “softness” of dioptase (5.0 Mohs) easily distinguishes them from hard emeralds (8.0 Mohs)—for those of you who identify minerals for treasure hunters.  In fact, in the late 1700s copper miners working at the Altyn-Tyube Mine in the Ural Mountains of Kazakhstan thought they had discovered a giant emerald deposit when suddenly beautiful green crystals started showing up.  I presume many of the green crystals were taken out via lunch bucket by the Russian and Kazakh miners before the mineralogists/chemists working in Moscow said, “sorry boys, too soft for emeralds.”  Even today the Altyn-Tyube in the premier collecting locality for dioptase and the source of my specimen.  
  
Dioptase forms in the oxidized zone as a secondary mineral where copper sulfides are the primary minerals. However, the formation of diopside is restricted to dry climates where circulating ground water has an alkaline pH (acidic solutions buffered by carbonates) and dissolved copper.  Dioptase is closely related to another copper silicate, chrysocolla.

And finally, dioptase may be, and has been, used as a pigment for painting.

The though for Monday:  Green is the prime color of the world, and that from which its loveliness arisesPedro Calderon de la Barca.

Sunday, January 5, 2020

YOOPERLAND COPPER AND ENGLISH FLUORITE


The Colorado Springs Mineralogical Society (www.csms1936.com) sponsors a number of interest groups that specialize in the study of areas such as fossils, crystals, lapidary and others.  In fact, the Society actually started when Lazard Cahn, a local mineral dealer with ties to New York City, “taught and studied” minerals and crystals to a group of local citizens interested in such.  From its crystal-orientated start in 1936 the Society morphed into the multi-disciplinary society seen today.
Although I have attended several different group meetings, and even organized the fossil group for a few years, my major interest (and committed time) today is with the crystal group.  Therefore, when it came time for a holiday party organized by Mr. Rockhounding the Rockies (https://rockhoundingkw.blogspot.com/) and The Gem Guy I began to organize my thoughts about which finger foods I could contribute, and a nice mineral or two for the secret gift exchange.  I was all prepared and ready to hit the country roads until 8.5 inches of snow, along with high winds, blanketed the area with some substantial drifts. The next night I was able to use aggressive tires and four-wheel drive to complete a safe trip to the party.


My secret gift received was a nice specimen of native copper collected from the Caledonia Mine, Ontonagon County, Michigan---a real Yooper Copper Nugget.  The Mine started production in ~1863 and continued until ~1958 although mining was sporadic after 1881.  There have been several exploration events since closing and even today the dump piles are available, with reservations, for specimen mining.  Maybe somewhere a little less than 1,500,000 pounds of copper has been refined rom the Caledonia.

Photomicrograph of a cavity in the copper nugget showing traces, perhaps, of both copper crystals and casts of dissolved calcite crystals, along with green epidote (see below). Width FOV ~1.2 cm. 
Photomicrograph showing massive epidote? with disseminated copper. Width FOV ~1.2 cm.

Bright, shiny, hacky copper nugget with blobs of massive, green epidote (I think).  The nugget was prepared by immersing it in an acid bath (unknown acid). Such a bath removes tarnish but also dissolves calcite and other carbonate minerals.  Near the center of the piece the large cavity displays casts of calcite crystals.  Width of nugget ~6.6 cm.
See the discussion on MinDat about cleaning copper at: https://www.mindat.org/mesg-26246.html#26266

I have commented on the origin of the Michigan Upper Peninsula (Yooper Land) copper, the massive outpouring of Precambrian volcanics, and the Midcontinent Rift System in a rather lengthy Posting on August 2, 2019.  No use repeating the information here.


Santa was responsible, so they say, for dropping off several “door prizes” with picking rights determined by lottery.  My lucky number was drawn last but, in my opinion, I received the premier specimen—some really nice cubes of fluorite collected from the Heights Mine (per label), Weardale Region, County Durham, England, UK.  MinDat describes the area as “the valley of the River Wear. The upper reaches between the town of Wolsingham on the east and the county border with Cumbria to the west is host to significant mineral deposits of the Mississippi Valley Type (MVT). Many mines in the area were developed for lead and iron between the 13th and 19th centuries, and for fluorspar during the 20th century. Significant amounts of stone quarrying have also occurred. Amongst collectors, the region is particularly known for the high-quality fluorite specimens [especially green] that have come from many of the mines… Associated minerals include galena, calcite, and aragonite. Larger, opaque green fluorite crystals to 8 centimeters have also been encountered.”

Although not shown below, many of the fluorite cubes fluoresce a bright violet color under Short Wave Ultraviolet Light. 

Interesting purple-tinted fluorite cube with a front penetrating twin. Width FOV ~1.2 cm.

Surface-pitted cube of light green tinted transparent fluorite.  Width FOV ~1.2 cm.

Very dark green cube of fluorite surrounded by "clear" and smaller cubes.  Width FOV ~1.2 cm.


Small crystals, some double terminated, crystals of quartz.  I am uncertain about the matrix but perhaps eroded and convoluted galena.  Width FOV ~1.2 cm.

Rather colorless fluorite cube. Width FOV ~1.2 cm.
The Weardale specimen with many fluorite cubes of all sizes.  Colors range from light green (upper left corner) to dark green (three cubes in lower left corner)) to colorless. Light purple tinted cubes on reverse.

At one time in my life I took a train ride through central and northern England since I wanted to spend a few days in the Lake Region, and to examine Hadrian’s Wall. The latter had fascinated me since a grade school history course.  It was a great trip except for one thing—the first morning in a hotel I was served Black Sausage with eggs.  I was hungry so chomped down the small portions but really was not fond of the sausage. It was only after eating that I found out the ingredients---and have never put a piece of Black Sausage in my mouth again.  In case you are interested in making the meat dish, here you go:
  Ingredients:
1 1/2 pounds groats (I like barley or rye berries)
1 pound pork shoulder (fatty)
½ pound fresh pork belly (skin off)
1 tablespoon salt
3 tablespoons marjoram
1/8 teaspoon clove
1/8 teaspoon cinnamon
½ teaspoon allspice
1 teaspoon caraway
6 cups blood
2 cups chopped onions
12 hog casings, 18 inches long





As for Yooperland, the locals are pretty taciturn, but may like blood sausage!