Sunday, December 18, 2016

Where to find iolite gemstones in nature

A group of faceted iolites set in a golden cross. Iolites are some of the more attractive
gemstones, but few jewelers keep them on hand because of their low-value.
Finding iolite gemstones is not easy as there are not many guides. But if your region of exploration has the right metamorphic conditions, such as in the central Laramie Mountains and possibly the Copper Mountain in the Owl Creek Mountains, you might consider searching for the gemstone. The conditions for metamorphic iolite deposits are favorable in regions where aluminum-rich schists and gneisses are found and where the metamorphic triple point was reached to produce regional kyanite schists, andalusite schists and sillimanite schists. 

Cordierite mica schist, Palmer Canyon. Three faceted iolites
 sit on the edge of a large iolite porphyroblast. 
First check to see if there are metapelites (also referred to as pelitic schists). These schists are aluminum-rich schists with aluminum-rich minerals such as mica, garnet, staurolite, andalusite, kyanite, sillimanite, cordierite and/or corundum. The mica schists should also contain some porphyroblasts. If you find any mention of cordierite in the geological literature in an area with these kinds of rocks, you may have chance of finding gem iolite.

Unfortunately, cordierite (iolite) has a low specific gravity, so panning streams for this gem is not possible. You just have start looking in favorable terrains. My recommendation would be to start where geological reports mention the presence of mica schist containing blue cordierite. Geologists, who are not taught to recognized gemstones, often describe the mineral but seldom mention transparency or gem-character. SO it is likely there are many iolite deposits described in various geological theses and geological survey reports that have been overlooked by geologists.

Another important characteristic is to search the literature for descriptions of kyanite, sillimanite and/or andalusite. These minerals form under similar conditions as metamorphic iolite gemstones.

Group of faceted iolite and ruby from Palmer Canyon, Wyoming
Beautiful, large iolite porphyroblast in mica gneiss from
Palmer Canyon, Wyoming.

Metapelite from Grizzly Creek containing kyanite

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The Gemhunter, a polymath of rocks, martial arts, stars, pencil, written word & public speaking. A Hall of Fame Martial Artist, Geologist, Author and Public Speaker. Look for numerous blogs by the GemHunter on gemstones, gold and martial arts designed to help the reader learn about these subjects.