March 1998

Gemstones & Pearls:Gemology


Collectors treasure these gems with their riots of spectral hues

While some inclusions in calcite are rare and highly desirable, moving "bubble" inclusions in natural voids that occur in calcite (and emerald and quartz) are even more so. The bubble inclusions are fascinatingly beautiful under magnification. This is a proven selling point for gem cutters who specifically place the inclusion in the most obvious location - the center of the stone. Retailers can use the same tack when pointing out interesting natural birthmarks to their own gem customers. Some inclusions are simply irresistible and are proof of the gem's natural identity.

You can romance these inclusions - all you need is a 30X to 60X microscope. You'll be able to see that properly placed in an iridescent calcite, inclusions do not take away from the beauty of the gem itself, especially when examined in a strong light source. This is when the iridescent cleavage planes in calcite catch light and break it into prismatic hues.

Iridescent calcite, with a Mohs hardness rating of just 3, is cut by only the most experienced cutters because of the distinct cleavage in three directions - the stones can break apart along atomic planes with a sharp knock. It requires highly experienced setters to mount the stones in jewelry.

Calcite is strongly birefringent at 0.172, which causes viewers to see strong "doubling" of the facet junctions when looking through a transparent gemstone. A "doubling" of the inclusion is seen in the most magnified photo on this page. This iridescent calcite was faceted by Michael Gray of Graystone Enterprises, Missoula, MT. Interestingly, the gas bubble can be moved around the void, much like in a carpenter's level, as the gem is tilted.

- by Robert Weldon, G.G.

   The cut of the stone placed this bubble inclusion in the center. Cut by Michael Gray, Missoula, MT.
   Iridescent calcite with bubble inclusions are prized by collectors.
   Magnified, the freely moving bubble is easily visible, as is the strong "doubling" effect due to calcite's strongly birefringent nature

All Photos by Robert Weldon.

Copyright © 1998 by Bond Communications.


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