Moonstone
A ghostly sheen moves under the surface of this feldspar, like moonlight glowing in water.
OVERVIEW
ABOUT MOONSTONE
Moonstone is a variety of the feldspar-group mineral orthoclase. During formation, orthoclase and albite separate into alternating layers. When light falls between these thin layers it is scattered producing the phenomenon called adularescence. Adularescence is the light that appears to billow across a gem. Other feldspar minerals can also show adularescence including labradorite and sanidine.
Moonstone is a birthstone for June, along with pearl and alexandrite.
ADULARESCENCE
Moonstone’s unearthly glow is caused by light scattering between microscopic layers of feldspar.
60%
The minerals in the feldspar family make up more than half of the Earth’s rocky crust.
0.5 MICRONS
Feldspar layers that create moonstone’s sheen are similar to the size of a wavelength of light.
FACTS
Mohs Hardness: 6.0 to 6.5
Chemistry: KAlSi3O8
Color: Colorless to White, Gray, Green, Peach, Brown
Refractive index: 1.518 to 1.526
Birefringence: 0.05 to 0.008
Specific gravity: 2.58
Mohs Hardness: 6.0 to 6.5
treatments
There are a number of processes used to alter the color, apparent clarity, or improve the durability of gems.
SYNTHETICS
Some gemstones have synthetic counterparts that have essentially the same chemical, physical, and optical properties, but are grown by man in a laboratory.
IMITATIONS
Any gem can be imitated—sometimes by manmade materials or by natural materials chosen by man to impersonate a particular gem.
WHY WE LOVE THIS GEMSTONE
1
RARITY
Rare in top qualities, this ethereal gem derives from one of the earth's most common minerals.
2
ADULARESCENCE
Stacked layers of orthoclase and albite diffract light, creating moonstone’s adularescence.
3
ANOTHER PHENOMENA
Besides adularescence, moonstone sometimes also shows a cat’s-eye effect.
QUALITY FACTORS
An assessment of the following characteristics determines moonstone’s value.
COLOR
The finest moonstone is a gem of glassy purity with a mobile, electric blue shimmer.
CLARITY
Characteristic inclusions include tiny tension cracks called centipedes.
CUT
As it displays moonstone’s phenomena to best advantage, cabochon is the common cut.
CARAT WEIGHT
Moonstone comes in a wide range of sizes and carat weights.
MOONSTONE QUALITY FACTORS: THE COMPREHENSIVE GUIDE
RESEARCH
Explore sources, gemological research, and the role of gems in history.
RECOMMENDED READING
Colored Gemstones: The Antoinette Matlins Buying Guide
Antoinette L. Matlins
Feldspar Minerals: Crystal Structures, Physical, Chemical and Microtextural Properties
Joseph V. Smith and William L. Brown
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