Monday, January 7, 2013

Deskcrop: Dumortierite and Dumortierite-Sericite Schist

These various rocks had been lying around on my kitchen table for weeks when I decided to photograph them together, along with a Bailey's glass filled with wine and an empty Alaska cup. Clockwise from the Bailey's glass: dumortierite-sericite schist with rose-colored dumortierite, greenish dacite porphyry from the Osgood Mountains, reddish volcanic rock from the Midas area, and lavender dumortierite schist.

The dumortierite-sericite schist is a from the Champion Mine area, located in the Rochester mining district of the Humboldt Mountains, Pershing County, Nevada.

Dumortierite-sericite schist, composed mostly of dumortierite, sericite (AKA fine-grained muscovite), quartz, and possibly andalusite.
Sheen from the fine-grained, clear to white sericite (muscovite) on foliation planes and disseminated in the schist.
Lavender dumortierite schist.
I found this one piece of lavender dumortierite schist on the ground below the chute of the ore bin between the upper and lower Champion Mine workings.

Dumortierite has been mined for use in making refractory ceramics such as those used in spark plugs. It is sometimes used as a gemstone (or rock), and the blue varieties have sometimes been used to make fake lapis lazuli.

By the way, these rocks are currently unlabeled. Andrew Alden has a good post up recommending that everyone label their rocks and minerals (with name and location or provenance). I will be able to label precisely all but the reddish volcanic rock.

Related Posts:
Friday Photo: Dumortierite
The Road to the Champion Mine
Rock Walls at the Champion Mine Lower Workings
Dumortierite at the Champion Mine, Nevada
Upper Champion Mine Workings

Selected Reference:
Mackay School of Mines staff, 1928, A bulletin by the Mackay School of Mines staff on the mineral dumortierite, University of Nevada Bulletin, vol. 22, no. 2: Nevada Bureau of Mines and Geology Bulletin 8, 47 p., including 1 oversized page.

2 comments:

Anonymous said...

Interesting--Dumortierite seems to be becoming the mineral of the year. A few weeks ago someone on Andrew Alden's forum vaguely described a cobble they found on the shore of one of the Great Lakes and wondered if it could be Dumortierite. I replied that, since Dumortierite was a rare borosilicate mineral, it was unlikely, and that I had never heard of Dumortierite, so had to look it up to see what it is. Then you showed us your Dumortierite mine shortly afterward, and now a deskcrop! It's nice to see what the stuff really looks like, even if I never do see it in "the wild". Thanks for sharing!

--Howard

Silver Fox said...

It is fairly rare: as of the 1928 MSM or NBMG bulletin, 7 U.S. states held known dumortierite localities: Arizona, California, Colorado, Nevada, New Mexico, New York, and Washington. It also occurs in at least one area in Ontario, and one (?) locality in Mexico.

Having seen it a long time ago at the Rochester area in Nevada, I had grown to think of it as fairly common (and easily collectible within a few hours of Reno).

So, come to Nevada if you'd like to see it in the wild! :)