Omphacite formula

OMPHACITE formula:

(Mg, Al) should be (Mg, Fe, Al)

Thank you.

I,m not sure that version is any more correct than the version we already have on Mindat now. Neither one of them depicts omphacite,s structure very well; both of them are too oversimplified to be useful... just looks like "dirty diopside". We need something more structural, that depicts the coordinated replacements. (or just abolish the species altogether :))

I think that omphacite is a mixture of diopside and jadeite.

Many minerals are actually mixtures.

I believe that Saul's inspiration derives from his interest in the lovely green uvarovite looking druses which have been identified by RUFF as omphacite. I think their morphology is more amphibole like, but I can't argue with one of our country's leading mineralogists.

The locality is one of the few eclogites known in Washington State. It occurs in the area of Little Deer Creek and Gee Point in Skagit county Washington. The host rock is the World's toughest rock. Barroisite Schist. Look up GSA publication Map and Chart Series MC61 by E.H. Brown. Also look for Claudia Owen's 1988 University of Washington PhD thesis "Petrogenesis of Shuksan Ironstones" . Bordering the ecologites are manganese iron pods with some exotic mineralogy which show mineralogy similar to Franklin, New Jersey. She reports freidelite on the slopes of Gee Point. I couldn't find that species, but it is easy to find rhodonite and bustamite group minerals with speckles of yellow spessartine.

The other ecologites occur near Crawfish Lake in Okanogan County. Very coarse pyroxenes with highly flourescent zircons. In the same area are some thick pegmatites with large pockets of smokies and pale green amazonite.

The location is on inholder lands within the Colville Indian Reservation. I tried to get a lease on the location from the tribe for access rights even though they don't own the land itself. No luck. Too much casino money. The Colvilles now have their own jails. Think of the movie "Midnight Express". I will never visit the Colville Reservation again even though I worked there for two years for Western Nuclear back in the 1970s..

Bart

Another reference that might be reviewed and considered for addition to the Omphacite page: Zhang, Qifang; Ma, Zhesheng and Shi, Nicheng (1999): Determination of crystal structure of omphacite. Chinese Science Bulletin, Volume 44, Number 10 (1999), 944-949. In addition to a proposed formula and site accommodations, the study reports 4 space groups (C2/c, P2, P2/n, P2/c) and indicates a possible fifth (Pn). [www.springerlink.com]

Just as an aside, here's an article I found interesting. [www.gia.edu]

Ron



Edited 1 time(s). Last edit at 08/04/2012 02:38PM by Ronald John Gyllenhammer.