Feldspars: Moonstones and Labradorite

The feldspars are a group of related minerals which, as a group are the most abundant minerals in the earth’s crust. However, only a tiny percentage of the feldspars fall in the “gem quality” range. The members of the feldspar group have similar chemisty, but some have different crystal structures. Physical and optical properties are very similar.

Moonstones

Moonstones have phantoms of flash! As you turn the stone the flash of color, the mysterious sheen, moves around the gem, appearing and disappearing. Moonstones are orthoclase feldspar with a sheen called adularescence. The most elite of the moonstones have blue flash or a rainbow of colors. The body color of these moonstones are colorless and semi-transparent. Tiny platelets which are too small to see create the adularescence, reflecting back shimmering color. Some colorless moonstones have a white flash. Blue flash and rainbow moonstones have recently become very popular. Once considered plentiful, they are now rather scarce due to increased demand and prices have gone up. Nevertheless they are still in the low price category for small stones under a couple of carats. Exceptional quality large blue flash and rainbow moonstones will command per carat prices in the moderate price category.

(Moonstone photo by ICA/Bart Curren)

The blue flash moonstones are primarily found in Sri Lanka; the rainbow moonstones are from India. More abundant and less glamorous are pastel colored translucent moonstones from India; many of these have an eye, if the stones are cut to display chatoyancy. Colors available include peach tints, light greens, yellows, and medium to dark grays. These moonstones are mystical in their appearance and low in cost. Today moonstones are often carved into mini art works. Some are even carved with “man in the moon” faces. The cost of carvings may fall into the moderate category if they are very unusual.

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Labradorite Gems

Labradorite, a mineral of the group, has many distinctive and exotic varieties which are considered gemstones. Rainbow moonstone is technically a labradorite variety.

Spectrolite

is dark translucent gemstone with an intense blue flash which is mined in Finland. Labradorite from Madagascar has minute black inclusions and a blue, green or golden flash. Heliolite is a variety mined in Oregon with a schiller effect that flashes out red, green, blue and orange; many of these have more than one color in each stone. This variety is generally faceted rather than cut into cabochons. Schiller is an almost metallic reflection created by minute inclusions in the stone. There are other varieties of labradorite such as colorless or light yellow transparent varieties; these lack an exciting appearance. Labradorite varieties generally run in the low price per carat range, but exceptional stones may demand more.

Amazonite

Amazonite is an opaque greenish blue variety of microcline feldspar. The finest amazonite is mined in Colorado but most commercial amazonite is mined in Brazil. This stone is in the low price range. If you are shopping for feldspar gemstones buy the gem that excites you. This mineral variety has phenomenal stones at a low price. If you like the unusual, a feldspar may be a good choice for you. When prices of the feldspar gemstones fall in the low range, the gems will not be heavily scrutinized to differentiate quality. There will be a wide range of stones with different personalities to choose from at the same price, so quality features are not as important an issue in this category except for the very finest stones. Of course, color and phenomena are the first considerations. Then examine the stones for any detracting flaws. Finally decide if the cut compliments the phenomenal aspects of the gemstone.

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Blue Moonstones
(Photo by ICA/Bart Curren)
Colors: Pastel tints of all colors
R.I.: 1.51 – 1.59 Range for the whole group.
Durability: Not very hard but they are reasonably tough
S.G.: 2.54 – 2.70*
Treatment: None known
Hardness: 6 – 6 1/2
Availability: Supply meets present demand
Localities: India, Madagascar, Labrador, Sri Lanka, Oregon
Price: Mostly low, some moderate exceptions
Common shapes: Cabochons: rounds and ovals

By Sondra Francis - © Gem Dealers' Secrets - Handbook for the Gem Buyer - 1999
All rights reserved internationally. Copyright © Sondra Francis. Users have permission to download the information and share it as long as no money is made-no commercial use of this information is allowed without permission in writing from Sondra Francis.
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About the Author
Sondra Francis has scoured every major colored gemstone market in the world since 1978. She was a charter member of the American Gemstone Association and served as a board member. She was a founding member of the International Colored Gemstone Association. A true gem lover, Sondra has marketed her treasures on the wholesale and retail markets.
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Acknowledgments
A special thanks to Pam Dulgar, Alex Edwards, Cheryl Kremkow, Kate Kirby, Helen Mitchell, Carol Morgan Page, David Pond, Elaine Proffitt, and Ray Zajicek for their help.
Photographs: Bart Curren and ICA Gembureau ; Alex Edwards, Pearl Sales Institute ; David Dikinis
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