iolite

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Iolite and amethyst cross pendant

Species:  Iolite
​​Mohs Hardness:  7 to 7.5 out of 10
Color:  Violet through slightly violetish blue, with strong eye-visible pleochroism.  Small stones appear grayish.
RI:  1.542 to 1.551 (+0.045 / -0.011)
Birefringence:  0.008 to 0.012
SR/DR/AGG:  DR
Clarity Type:  Type II
Optic Character:  Biaxial negative
Fluorescence:  Inert
SG:  2.61 (+/-0.05)

iolite facts

Photo courtesy of Ritani

​Iolite is strongly pleochroic.  You'll see 3 distinct colors in 3 different crystal directions.

Iolite is one of the few gemstones that is not typically treated in any way.

Iolite is the 21st wedding anniversary gemstone.
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All photos courtesy of Scott Papper, GIA GG, AJP, CMA (NAJA)