Way back in the mid-1960s I took my first field trip
to the Black Hills of South Dakota and had an opportunity to view and collect
some of the lithium minerals, especially spodumene [LiAl(SiO3)2],
amblygonite [LiAl(F,OH)2Al9SiO4)3],
and lepidolite [K2Li4Al2F4Si8O22].
Later in life, thanks to Mr. Rockhounding the Rockies, I found that a lithium
mica is available in the Pikes Peak region—“zinnwaldite” [Li2K2Fe2Al4Si7O24]---see
Blog posting November 24, 2013.
The spodumene crystals in the old mines of the Black
Hills were fantastic and reached great lengths---in the old days miners located
specimens about 40 feet. South Dakotans
also taught me that the gemstones kunzite (pink) and hiddenite (green) are
colored sections of spodumene (see Blog posting July 2, 2013).
Lithium is an important element and used in a
variety of commercial applications. Most
of us are aware of lithium batteries and lithium grease but were you aware that
a lithium isotope (Li-6) is used in the production of “heavy hydrogen”
(tritium)? So what? Well tritium plays a critical part in
thermal-nuclear explosions---hydrogen bombs!
Natural tritium is quite rare on earth so nuclear activation of Li-6 in
the reactors produces tritium (as do other methods such as using heavy waters).
As I understand the situation (and that is a stretch
at times), all lithium extraction in the U.S. now comes from lithium-rich
brines and production seems limited to Nevada.
Wyoming has large reserves; however, I do not believe production is
current. So, the hard rock mining that
produced tons of lithium from the Black Hills is no more.
This last February at one of the side Tucson sites
(my favorite kind) I came across a specimen of holmquistite. So, I pulled out
my cheat sheet and found out it was lithium amphibole. Now, I am a sucker for non-expensive
minerals, especially those minerals with names that I never learned about in
mineralogy class. Heck, I can hardly
remember the definition of an amphibole---except that I got them mixed up with pyroxenes!
So, I was able to pick up the lone specimen of holmquistite for a couple of
bucks.
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| Thin bladed prismatic crystals of holmquistite. Width of crystal mass ~1.1 cm. Collected Fu Yu, Artal, Xiangjiang Province, China. |
My friends at MinDat described holmquistite [Li2{(Mg,Fe++)3Al2}Si8O22(OH)2] as forming “prismatic or acicular crystals up
to 10 cm or as columnar sheaflike, massive aggregates. The colour varies from
black, dark violet to light sky-blue.” It belongs to the Orthorhombic Crystal
System and is found as “metasomatic [hydrothermal fluid] replacements near the
outer margins of lithium-rich pegmatites”---along the wall rock contact. There
are several other minerals described in the “Holmquistite Group” and interested
readers should see MinDat for additional information. Thin bladed prismatic crystals of holmquistite. Width of crystal mass ~1.1 cm. Collected Fu Yu, Artal, Xiangjiang Province, China.
Holmquistite is a fairly rare mineral that needs
other lithium minerals (spodumene, petalite [LiAlSiO4O10])
in close association in order to form. I
find it interesting that the lithium-rich pegmatites in the Black Hills seem
almost devoid of holmquistite. Small
amounts have been identified from the Edison Mine near Keystone but otherwise
it seems absent. I am uncertain of this
omission. Other localities producing
minor amounts of the mineral include Maine, North Carolina, and New Mexico. As
far as I can tell, holmquistite is a specimen mineral and not readily mined for
lithium.
Picking up a rare specimen like holmquistite is one
of the reasons small venues are exciting.
One never knows what lurks on the next table!
Sometimes
minerals are beautiful.
Not in looks.
Not in what they say.
Just in what they are.
Apologies to Markus
Zusak Not in looks.
Not in what they say.
Just in what they are.