BLUE LAVENDULAN: TUCSON 2016

The Kino Gem and Mineral Show is one of the larger venues housing items for sale at the Tucson shows.  In 2016 there were 205 vendors listed; however, it seems increasing difficult to purchase individual mineral or rock specimens.  Instead there are a wide variety of somewhat bizarre items for sale including guns (this is Arizona), “coon skin” hats complete with tails, authentic animal fur and skins, incense, gongs and brass items direct from Asia    The tents are set up at the Kino Sports Complex in south Tucson and are a mixture of individual tents and the large football field size units.  One large unit houses dealers displaying a great variety of lapidary machines while another tent has smaller kiosks stocked with overpriced jewelry.  What is missing are the small mom and pop operations that were once the heart of the venue---essentially booted out.  But life goes on as buyers could locate a great variety of amethyst cathedrals and smaller broken pieces. 

I do like the colors in this large concretion with internal agate banding.

And away we go to explore the offerings.

I always enjoy seeing specimens collected from siliceous hot water deposits near Milford, Utah.

Anything you need from southeast Asia, except rocks and minerals.

Here is my favorite guy at the venue offering tasty snacks.

So this is Arizona and maybe rockhounds need to shoot claim jumpers.  Of course it is not uncommon to see, as Marty Robbins sang, "the big iron on his (her) hip."

Every rockhound needs genuine hide or fur to line their cases and drawers.

I always thought these were natural lingam stones but now realize they are linga (plural). I also believed they were collected by natives from a sacred river in India.  Somehow doubts creep in when I see thousands and thousands for sale in the US being pawned off as Hindu religious items guaranteed to increase your masculinity.

At last a shop selling rocks and minerals!

What appears as a crust of blue lavendulan (copper arsenate) is actually hundreds of tiny thin platy crystals; however, they measure in individuals less than 1 mm and are beyond the range of my scope.  The R points to one of a cluster of radiating individual crystals.  Total width FOV ~ 7 mm.

And, looking really hard at some stock I was able to locate a really nice piece of blue lavendulan.  The specimen appears as sort of a crust of intense electric blue on the matrix.  However, on closer examination under high power one can observe the crust is actually composed of very tiny aggregates of thin platy crystals, some of which form rosettes. An older label indicates collection at El Guanaco Mine, Santa Catalina, Antofagasta Province, Chile where MinDat noted 31 valid minerals and two type localities.  At the mine copper and gold veins are emplaced in Upper Cretaceous and Paleocene volcanic sequences.  I presume, but am uncertain, that both the copper and the arsenic could be the result of oxidation of the primary mineral, enargite [Cu₃AsS₄].

Lavendulan [NaCaCu₅(AsO₄)4Cl-5H₂O] is a hydrated copper arsenate and forms as a secondary mineral in “oxidized zones of some copper deposits” (MinDat).  So far, so good; however, I need to rely on the label for identification since a very similar mineral, lemanskiite, is known from the location (discovered in 1998).  In fact, the mine is the type locality for this copper arsenate.  Lemanskiite and lavendulan have exactly the same chemical formula but belong to different crystal systems-they are polymorphs.  Lavendulan is Monoclinic and lemanskiite is Tetragonal.  Trying to visually identify lavendulan from lemanskiite is above my pay grade!

As noted in other postings the arsenate radical (AsO4) is similar in size to the phosphate radical (PO4) and they often interchange.  Well, sampleite is a copper phosphate in a solid solution series with lavendulan.  If one substitutes lead for the calcite in lavendulan the mineral becomes zdenekite.  Learning is “fun”! 

So I am calling these tiny crystals lavendulan since I don’t carry around an XRD or something but knowing I well could be wrong!  These great- colored crystals have a vitreous to maybe a sub vitreous luster, are brittle, translucent, commonly cleave or fracture, and are quite soft (~2.5 Mohs).  Looking closely one can observe twins and the streak is a light blue.

I love life.  There’s so much to learn and see all of the time, and nothing nicer for me than to wake up, and the sky is blue.   Pattie Boyd