Hello Cynthia Bach:
Thank you very much for your answer to my iolite question. People kept
telling me it wasn’t that durable, but when I looked it up in my books,
they said the hardness scale was the same as garnet (7 to 7.5). Now I
understand the concept of two different measurements. Does the
toughness scale have a name, and is it listed anywhere?
In the GIA’s Gem Reference Guide it lists Iolite as having a Moh’s
hardness: 7 to 7 1/2, Toughness: fair , Stability: Reaction to Heat -
fusible, Stability to Light - stable, Reaction to Chemicals - attacked by
acids. Why would the GIA even have a listing for “Toughness” and a "grade"
to quantify it?
Faceting For Amatures, Second Edition by Glenn & Martha Vargas will list a
"Toughness Scale" in comparison to Moh’s hardness scale. This deals with
durability in cutting and translates to wearability too.
GemData, Mine Design & The Spectrum Network at http://www.gemdata.com
of the original interactive “Gem, Mineral & Jewelry Show Calendar” Colored
Gemstones, Diamonds & Cutting Rough Databases and Information SoLux
Daylight Lighting, email Lance Kanaby: mailto:@Lance_Kanaby