Gem/Gem Topic of the Month

Each month this section will feature either a topic of interest to gem lovers or one special gemstone with background on the material and its value.

Go to: Homepage -- what's new in faceted gems -- what's new in designer cabochons and gem carvings -- gem of the month -- gem of the month archive -- birthstone of the month -- key to all the codes used on the ACS site -- definitions of terms used on the ACS site -- how to order -- about ACS -- about the ACS cutters -- settings for these gems --faceting information -- purchase UltraTec equipment

 

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May, 1998 (Revised, August, 2004)

Benitoite

 

Benitoite is the quintessential American gemstone. Gem quality specimens are mined nowhere in the world except in San Benito County, California. Adopted as the California State gemstone, it is a favorite with collectors who admire its beautiful blue body color and its dispersion (.044) equal to diamond.

Dispersion has the potential to cause stones to twinkle with flashes of red and green, although there is a trade-off between dispersion and body color. Some admirers are willing to forgo the dispersive display to get a darker blue stone, while others admire a lighter stone in which dispersion is more evident. The stone below shows a balance between rich body color and visible dispersion.

At hardness 6.5 it is tough enough for most jewelry applications. Its scarcity, however, makes it virtually unknown to the general public. The flattened triangular crystals are usually small and highly dichroic showing blue and colorless. Obtaining the blue color usually means orienting the crystal for lesser yield. Finished gems are almost always under 1 carat and usually less than .5 carat. No treatments or enhancements are known for Benitoite. It is truly one of the most beautiful (and wearable) of the collector gems.


Value

This gem is quite expensive, especially for rich blue, clean stones at carat and above sizes. Clarity enhances value, especially in stones eyeclean or better. Very light and very dark stones are on the lower end of the value spectrum with medium dark stones at the pinnacle. Perfection of cut is sometimes sacrified, even by the custom cutter, to achieve the largest possible gem so windows and less than optimal proportions are fairly common.


Gemological Data

Makeup: a barium, titanium silicate

Luster: Vitreous

Hardness: 6.5

Crystal structure: Hexagonal

Fracture: conchoidal

Density: 3.67

RI: 1.76-1.80

Birefringence: .047

All text and images, unless otherwise designated, © 2004 Barbara Smigel


Stones Currently Available:

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Go to: Homepage -- what's new in faceted gems -- what's new in designer cabochons and gem carvings -- gem of the month -- gem of the month archive -- birthstone of the month -- key to all the codes used on the ACS site -- definitions of terms used on the ACS site -- how to order -- about ACS -- about the ACS cutters -- settings for these gems --faceting information -- purchase UltraTec equipment