Tanzanite

This is the first in a series of blogs featuring gemstones other than the big four (diamond, ruby, sapphire and emerald). Each monthly blog will feature a different colored gemstone. The correct division of gemstones is white and colored. There is only one white gem-diamond. All others (including several in clear/white) are called colored gemstones.  Several of the colored gemstones are rarer and more valuable than diamond.

Tanzanite is a variety of the mineral zoisite.  Zoisite is a calcium aluminum silicate (Ca₂Al₂(SiO₄)₃(OH).  Tanzanite has a hardness of 6.5 to 7, which places it between feldspar and quartz on the Moh’s scale.  This also means that common dust (predominately SiO₂) will scratch the surface.  Thus jewelry with tanzanite should have a protective setting and not be used for pieces that will be subject to exposure.  The stone is named for the country where it is to be found.  The natural rough is usually tinged or colored yellow to brown.  When heated to 400 to 500 degrees centigrade, the color is enhanced and the yellow/brown disappears.  Rough tanzanite is only mined in one location in Tanzania.

When heat treated and then faceted, tanzanite produces a beautiful blue stone.  The hue and saturation of the stone should be rated 5/6.  Pale (low saturation) stones have a greatly decreased value.  The clarity of the faceted stone should be internally flawless when viewed with a 10x loupe.  Clarity of a stone should always be evaluated using a 10x loupe.  Higher magnification can be deceiving as the depth of field decreases with increasing magnification.  Value of tanzanite stones is up to $1500 per carat for a 5 carat or greater stone.  Inclusions in the stone and poor quality cutting will greatly decrease the value of the gemstone.  Since tanzanite is also blessed with perfect cleavage, care must be taken during cutting and setting so the stone does not split along a cleavage plane.

Tanzanite can produce beautiful jewelry!

References:

Schumann, Walter; Gemstones of the World, 3^rd Edition; Sterling, New York

Crowe, Judith; The Jeweler’s Directory of Gemstones; Firefly Books, Buffalo, NY

Wise, Richard; Secrets of the Gem Trade; Brunswick House Press, Lenox, MA

Posted by Rasmussen Gems and Jewelry LLC

 

 

 

 

 

 

 

Tags: gemstone facts, gemstones, Handmade, Handmade Artists, handmade rings, learning about gemstones, Tanzanite

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