Iolite

Iolite Information

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CHEMISTRY (Mg,Fe2) Al4Si5O18
CRYSTALLOGRAPHY Orthorhomic
REFRACTIVE INDEX 1.522 - 1.578
HARDNESS 7 - 7.5
SPECIFIC GRAVITY 2.53 - 2.78
CLEAVAGE Distinct 1 direction
HEAT SENSITIVE No

WEARABILITY* Very Good
SPECIAL CARE INSTRUCTIONS None

ENHANCEMENTS None

*Wearability is graded as Excellent, Very Good, Good, Poor, and Forget It!
For more details see the article on "Hardness and Wearability."

Iolite      This stone, which represents one of the few relatively available and affordable blue stone options, is rapidly gaining in popularity. Arguably the gain is due more to exposure in mail order catalogs and on cable shopping channels than to promotion by traditional jewelry stores. Run of the mill stones often have a steely, inky or washed out blue color, but the best specimens can rival AAA tanzanite in the saturation of their blue-violet hue.
     Iolite is frequently step cut to enhance color and often windowed and/or shallow cut to lighten tone. The cutter must orient the rough carefully, taking iolite's trichroism of blue, gray and near colorless into account. So far, no treatments have been successfully used to lighten color or to remove inclusions, so one can assume that gems are untreated.
     Its hardness of 7-7.5 makes it a suitable jewelry stone, though the presence of cleavage must be taken into account and some care exercised. Most of the iolite in world commerce comes from India, but substantial amounts are also mined in Tanzania, Brazil and Sri Lanka.

VALUE CONSIDERATIONS

     Sinkankas lists the wholesale value of fine blue violet stones in the 1 to 5 carat range as $60 to $80 per carat and $100 to $150 per carat for stones 5 to 10 ct. He also notes that stones larger than 8 carats are rarely eye clean. Federman is more conservative, listing retail values as $100 and $150 per carat, respectively, for those size ranges. Writing in 1990 he reports that German cutters have been buying iolite rough in quantity to capitalize on an expected surge in popularity and price.

Text and photos courtesy of Barbara Smigel at Artistic Colored Stones.

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