Monday, January 27, 2020

ELK CREEK BARITE: BEST $3 MINERAL FROM DENVER


Back in the olden days, that would be late 1960s, the Charcoal Lounge (AKA Char Bar) was one of the anchors in downtown Vermilion (as seen in this 2017 photo--it looked the same in 1965).  The Char Bar was a 21 establishment since it served "hard liquor."  That meant the underclassmen were relegated to the "beer bars" such as the Varsity.  Grad students frequented the Char Bar after the "housemother" locked the female dorm doors at 10:00 on weekdays.  Male undergraduates were allowed to roam the town and closed the beer bars at 2:00 AM or so.  Change the cars and downtown main street in Vermilion would be easily recognizable to any student of the 1960s.
The summer of 1966, a long time ago, was an exciting time for a newby geologist exploring South Dakota.  I had graduated from Fort Hays State University in Kansas in Spring 1965, went to summer field camp (a rite of passage for geologists) in summer 1965, and in the fall headed north to the University Of South Dakota to hopefully be awarded a graduate degree (I was uncertain about my skills and that event happening).  But it did in Summer 1967.

The Fall 1965 semester was a tough one for me as I had to learn a different method of studying for some “hard courses” such as Optical Mineralogy!  But, I survived, and actually made many new friends and passed the courses.

 I addition, I learned to count numbers in Spanish as the Number 1 Hot Billboard Hit for 1965 was no less than Wooly Bully by Sam the Sham and the Pharaohs:

Uno, dos, one, two, tres, quatro
Matty told Hatty about a thing she saw
Had two big horns and a wooly jaw
Wooly bully, wooly bully


Spring 1966 was spent looking down the scope in Optical Petrography, and trying to come up with a topic for my thesis.  Seems simple but my two favorite professors pulled up stakes and left for greener pastures (and larger departments and larger salaries).  I was left without a guide but located a thesis with the great help of a geologist working next door at the South Dakota Geological Survey.  So Summer 1966 saw me working for the Survey out of Chamberlain studying landslides in the Cretaceous Pierre Shale.  This was pre-Interstate 90 in much of South Dakota and the Survey and “road builders” were rightly concerned about building a stable road bed on a shale filled with bentonite seams (it swells when wet) and "slippery" bedding planes.  I learned as much about land slides as I ever wanted to know—but I was learning, and learning has always made me "happy."!
Exploring the agate beds, western  South Dakota, summer 1966.
On Friday afternoons I usually headed out to my thesis area south east of the Back Hills in the western part of the State rocking out with the AM tuned to Tommy James and the Shondells with
Hanky Panky:

My baby does the hanky panky
I saw her walking on down the line,
you know I saw her for the very first time,
a pretty little girl standing all alone,
Of course males of all ages dreamed about meeting up with that girl!
Often I would take a break from driving west in the middle of numerous Airstream caravans (remember those terrible things) all bunched up in a group on the narrow US 16 highway. One of my favorite stops was near Wasta where the highway goes into a deep valley and crosses the Cheyenne River.  The Cheyenne is the major drainage of the Hills and a few miles north of Wasta the River receives Elk Creek, also flowing east from the Black Hills.  There are wonderful exposures of the Pierre Shale along the River and Creek and, at that time, large concretions were abundant, especially along Elk Creek.  One simply had to pound on the concretions to find ammonite cephalopods, and calcite and barite crystals.   

A large calcareous concretion in the Pierre Shale.  Hat for scale.
Well, as with many things, the good stuff disappears over the years as moving from residence to residence takes its toll.  I did save a few ammonites and crystals but “lost” many more.

Photomicrograph of dark golden/amber barite collected from Elk Creek, South Dakota.  Length of crystal is ~1.7 cm.
The Pierre at Elk Creek has produced and is still producing (if you have the money to pay landowners), some of the finest barite (barium sulfate, BaSO4 ) crystals in the world.  Roberts and Rapp, in their seminal book Mineralogy of the Black Hills (1965), noted that superb crystals of barite from the Pierre concretions are colorless, yellow, amber, smoky brown, or wine colored and often are quite transparent. In fact, these barite localities were noted in the 2008 publication American Mineral Treasurers (published by the Mineralogical Record) as one of the top 50 American mineral specimen producing localities. The most collectable, and most expensive on the market, seem to be amber to light yellow in color, are water clear and gemmy, have a perfect chisel-shape termination, and posses a vitreous luster.  My collection from the 1960s does not have the perfect crystals but they were fun to collect.
The great specimens of Elk Creek barite exhibited by The Collectors Edge (Golden, Colorado) at the Tucson Show (2017?) and priced to sell at $75,000.
So, at the 2019 Fall Denver Area Mineral Dealers Show (see previous Posts) I was elated to acquire, for the sum of $3, a single crystal of Elk Creek barite that is gemmy, water clear but with an amber/gold tint, and has a chisel termination, and a vitreous luster.  Although the Elk Creek crystals display a number of shapes my newly purchased specimen is very tabular with well developed edges.  Barite belongs to the Orthorhombic Crystal System therefore  the “length” of the flattened crystal is along the B Axis rather than the C Axis (common in many minerals).  In fact, the length of the C Axis on this specimen is the “shortest” of the three axes.

Unfortunately is was impossible to get a good photo of the specimen that would do it "justice."  The top photo was taken with a decent point and shoot camera.  I wanted to show the transparency but note the included ghost crystals in the lower right corner.  The bottom is a photomicrograph that does not show the true color as the specimen is water clear and only slightly tinted (I tried to fix it using my novice skills with Photoshop but no luck). The digital photomicrograph is looking down the short C Axis through the tab while directions of the A and elongated B axes are indicated.  A fragment on the right side has broken out (after purchase) along some cleavage planes.  The numbers along the crystal faces are Miller Indices and the 001 is parallel to a face on the reverse. 

   
My parents were like those of Daniel Schwartz and tolerated a small town kid collecting rocks and minerals.  But perhaps more importantly they encouraged learning and education.  There was never any question in their minds, nor in mine, that I was headed to college after high school.  For this support I am grateful. RIP.
   
My parents were willing to spend time and invest time in my hobbies, no matter how odd they seemed. When I was young, I collected rocks and minerals… It was not the most eventful childhood, but I think that's good. Daniel Schwartz

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.