Canadian Rockhound: Cordierite

Home

Cordierite
By Doug Miller, Saskatoon, SK, Canada

Cordierite, (Mg,Fe)₂Al₄(Si₅O₁₈), has been found along the shores of Middle Foster Lake in northern Saskatchewan. Cordierite, also called iolite, is orthorhombic, has a hardness of 7 and a specific gravity between 2.55 to 2.75. This mineral has very strong pleochroism, typically exhibiting colors of blue, violet and straw yellow in the associated crystal axes. The pronounced pleochroism is easily observed and can be used in identification. Cordierite makes a very attractive gemstone when cut, but care must be taken to correctly orient the stone for the best blue color.
The cordierite found at Middle Foster Lakes occurs as non-gem quality blue crystals measuring up to 5 cm but typically less than 3 cm in pegmatite stringers in gneisses along the southern and eastern shores. Associated minerals include garnets and black tourmaline crystals (schorl) measuring up to 8 cm.

©1997 Doug Miller
E-mail: mildg@sk.sympatico.ca
This article may not be copied, distributed or reprinted in any form without the author's permission. To contact the author, please use the e-mail address provided. If you are unable to contact the author, please contact the Canadian Rockhound. Authorized reprints must acknowledge the author, original source and the Canadian Rockhound, and include the website URL address of the Canadian Rockhound.
The preceding article was first published in the February 1997 issue of the Saskatoon Lapidary and Mineral Club Newsletter. Reprinted in the Canadian Rockhound with permission.

More on Copyright

Document Number: win97_cordierite