AZURITE AT GOLD HILL

GOLD HILL ORE CHUTE

I recently noted the occurrence of the occurrence of adamite, a zinc arsenate hydroxide, in my miniscule collection of minerals from Gold Hill, Utah.  A couple of readers (wow, I didn’t know if anyone read these blogs or not ) confirmed the mammillary structures are goethite pseudomorphs after smithsonite!  Another reader suggested that the tiny acicular spray in the vug might be olivenite, a copper arsenate hydroxide [Cu₂(AsO₄)(OH)] that is common at Gold Hill.

In examining tiny pieces of minerals in my collection box I did notice “some blue” color.  I may be color blind with red-green-brown but can spot blue or purple (but I get them mixed up).  Initially I thought the streaks were linarite as a crust rather than small clusters of crystals.  Linarite is a secondary lead copper sulfate hydroxide that is found in the oxidation zone of ore bodies containing lead.  It has that beautiful azure blue color.

CRUST OF AZURITE WITH BOTRYOIDAL HABIT (TOUGH TO SE WITH THIS POWER).  LEFT TO RIGHT IS ~6.2 MM.

However, under high power of my binocular microscope I was able to notice a botryoidal habit rather than tiny crystals common to linarite.  This revived my brain cells and caused me to pull out the acid and I noticed the blue mineral “fizzed” indicating a carbonate.  So, I am now “guessing” (that is what paleontologists do with mineral identification) that the blue streak is common azurite, a carbonate of copper [Cu₃(CO₃)(OH)₂)], with a beautiful azure blue color.  So it goes.

By the way, the Rockpick Legend Co. in Salt Lake City has a wonderful collection of Gold Hill minerals and a great web site at:  

http://www.rocks4u.com/gold_hill.htm

mike

PHOTOMICROGRAPH OF AZURITE CRUST FROM GOLD HILL.  tHE FIELD OF VIEW IS ~2.4 MM.

WENDOVER WILL AND ADAMITE

WENDOVER WILL, ALL ~65 FEET WITH A MECHANIZED WAVING HAND, BECKONED VISITORS TO THE STATE LINE CASINO IN WENDOVER, NEVADA. AFTER 120 MILES OF BONNEVILLE SALT FLATS UTAHANS WERE READY FOR A LITTLE ACTION AND AN ADULT BEVERAGE.  PHOTO COURTESY OF WENDOVER HISTORY

Gold Hill is one of those classic collecting areas for Utah rock hounds, and those others pilgrims willing to travel to the far western reaches of that fine state.  Of course, the bi-state town (Nevada-Utah) of Wendover is on the route if one is interested in mining recent gold or needing a motel room and an adult beverage.

In the “old days” I had a research area down west of the Deep Creek Mountains to the south of Wendover and my crew always wanted to stop at the casino for a “good meal”.  They seemed not to really like my cooking campfire meals down in the desert!  So, it was off to the Stateline Hotel and Casino (currently operating as the Wendover Nugget Hotel and Casino), home of Wendover Will.  Seems like a entrepreneur by the name of Bill Smith operated a gasoline station in Utah (right east of the state line).  Never one to miss an opportunity,  when gambling was legalized in Nevada in 1931 Bill added a casino across the state line!  During the years that I was stopping in for a refreshment before heading to the desert, the vehicle was parked in Utah, we crossed a white painted line, and voila---we we in a different world with Wendover Will  welcoming all.

Leaving the world of bright lights and tinkling slot machines behind we heading south but often could not resist a side trip to the old mining town of Gold Hill, Utah.  I previously wrote about the mines and collecting conichalcite, a bright green copper calcium arsenate hydroxide, [CaCu(AsO₄)(OH)]---see that blog on December 8, 2011. The information sign at Gold Hill notes that the usual gold, silver, copper and lead were initially mined but when those minerals became depleted, the boom was over and the town became a ghost.  During World War I, arsenic was in demand as insect control for creatures devastating the cotton fields of the southern U. S.  So, Gold Hill opened up again and mined arsenates. 

COLORLESS AND VITREOUS ADAMITE CRYSTALS ON LIMONITE. SPECIMEN IS 4.3 CM WIDE.

Another mineral that Gold Hill is “famous for” is adamite, a zinc arsenate hydroxide [Zn₂ (AsO₄)(OH)]. Adamite is one of those minerals that usually occurs in the oxidized or secondary mineralized zone where zinc is present, and arsenic was in the hydrothermal solution. 

MODIFIED ORTHORHOMBIC AND COLORLESS CRYSTALS OF ADAMITE.  INDIVIDUALS ARE .5MM OR LESS IN LENGTH.

 Most of the Gold Hill adamite that I have seen is composed of very tiny crystal druses or ball-like clusters that are either yellow or various shades of green in color.  It appears that either iron or copper make some element substitutions.  However, pure adamite is colorless, transparent and quite vitreous. In fact, I paid little attention to my specimen of ademite from Gold Hill since I thought it was just “sort of a pretty” rock with numerous tiny quartz crystals.  But, much to my amazement, under high power of a binocular microscope those tiny crystals (mostly modified orthorhombic) turned out to be colorless adamite.  Some may have hints of very pale green but with my color blindness, it is hard to tell!

A VUG IN THE SPECIMEN CONTAINING AN UNKNOWN SPRAY OF MINERALS.  THE LONGEST INDIVIDUAL ROD IS ABOUT .5 MM.

CLOSE-UP PHOTOMICROGRAPH OF UNKNOWN MINERAL.  ANY IDEAS?

I tried to find other associated minerals in my small specimen,such as austinite, but no luck.  However, there are tiny mammillary structures that are either goethite or limonite, perhaps ?pseudomorphs after smithsonite.  And, there are a few sprays of an unknown mineral present!

PHOTOMICROGRAPH OF TINY MAMMILLARY STRUCTURES OF GOETHITE OR PERHAPS LIMONITE.  ARE THESE PSEUDOMORPHS AFTER SMITHSONITE?

I just need to revisit Gold Hill and do some dump digging; however, it is a fair trip from the Springs and with the price of diesel….!  But wait, all I would need is a couple of lucky pulls on the machine :)
mike

CARTOON OF MODIFIED ORTHORHOMBIC CRYSTALS COMMON TO ADAMITE.