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| "Big rocks" are still available for purchase at several Kino dealers. |
The shows at Kino, the ex-Tucson Electric Park
shows, have changed in the last couple of years. At one time the venue was stacked with small
dealers selling a wide variety of interesting rocks and minerals. Most of these mom & pop dealers were set
up on the soccer fields; however, the fields are now off limits and most of
these small dealers have moved to the 22nd Street venue. The remaining dealers, and there are many,
still peddle a wide variety of goods including Bob Marley reggae shirts,
“Persian” rugs, welded steel animals and “big” rocks with quartz crystals or
azurite. There also are plenty of beads
and amethyst cathedrals. I am always
amazed at how many tens/hundreds of thousands of beads are for sale each year
in Tucson.
There are some decent vendors with minerals for sale
but it seems that Deccan Plateau zeolites were the most common. I was impressed with the numerous vendors
selling lapidary supplies and equipment.
I am not interested in such, but the prices seemed decent. One thing that I did miss was the “golf cart”
hauling visitors from the parking lots to the show venues---it seemed to
disappear this year.
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| Take your choice of beads at various prices and designs. |
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| Large slabs of selenite gypsum quarried in Utah. |
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| A "tent" full of vendors. |
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| Several vendors had quality lapis for sale with accompanying high prices. |
I did locate a small dealer from Kansas (my original
home state) willing to “talk” minerals (and Jayhawks) and tried to convince him
to bring his wares to the CSMS Show in June.
At any rate, he had a small selection of “half-price” specimens so I
nabbed a couple. One was a carbonate
that was not in my vocabulary—Kutnohorite [Ca(Mn,Mg,Fe)(CO3)2]. Since the purchase I have been reading about
it, and examining such under the scope.
It seems a fairly rare mineral, a calcium magnesium carbonate related to
dolomite [CaMg(CO3)2], and in a series with ankerite [CaFe(CO3)2].
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| Photomicrographs of deep red, gemmy andradite (garnets) crystals with a druse of tiny crystals of bladed white-pink kutnohorite. Lower left andradite crystal ~2 mm in width. The camera did not pick up the mineral colors. |
Most of the time kutnohorite consists of aggregates
of tiny bladed crystals that are brown to pale pink or pale white in color. The
pink hue increases as the magnesium increases while iron imparts a light brown color.
Most of the time the mineral is quite dull or earthy in luster, somewhat
translucent, and has a hardness of ~3.5-4.0 (Mohs). When fractured, the end
result is a number of tiny conchoidal pieces.
My specimen came from the N’Chwaning II Mine in the Kalahari
Manganese Field, where the manganese deposits are in the Hotazel Formation of
Proterozoic age (Precambrian). This is largest
land-based sedimentary manganese deposits in the world, perhaps covering ~425
sq. miles. The ore has been subjected to hydrothermal alteration (temperatures
up to 450°C) and metamorphism and is rich in braunite, bixbyite, hausmannite,
marokite and hematite together with minor amounts of calcite. Andradite and
barite are common gangue minerals. Additional minor minerals include tephroite and rhodochrosite as well as
aegirine (http://wwwu.edu.uni-klu.ac.at). The origin of the giant manganese deposits has
been debated for many years. “Proposed models cover a diverse spectrum of
genetic processes, from large-scale epigenetic replacement mechanisms, to
submarine volcanogenic-exhalative activity, to purely chemical sedimentation
whereby the influence of volcanism is of reduced significance” (Tsikos and
Moore, 2006).
The Kalahari Manganese Field, Northern Cape
Province, South Africa, is the world’s most prolific producer of manganese.
This mining region has produced some of the world’s finest rhodochrosite and
hematite, as well as the finest ettringite, sturmanite, olmiite, sugilite,
inesite, hausmannite, and thaumasite. Two of these mines (Wessels and
N’Chwaning II) are together type localities for 19 species, including
diegogattaite, wesselsite, lavinskyite, manganvesuvianite, marshallsussmanite,
and sturmanite (www.mineralspecies.com).
REFERENCES
CITED
Tsikos, H. and J.M. Moore, 2006, The
chemostratigraphy of a Paleoproterozoic MnF- BIF succession -the Voelwater
Subgroup of the Transvaal Supergroup in Griqualand West, South Africa: South
African Journal of Geology, v. 109.