HOLMQUISTITE: RARE LITHIUM SILICATE

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.

 

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