25 March 2019

JUNE BIRTHSTONES – ALEXANDRITE Green in sunlight. Red in lamplight. Color-changing alexandrite is nature’s magic trick. Often described by gem aficionados as “emerald by day, ruby by night,” alexandrite is the very rare color-change variety of the mineral chrysoberyl. Originally discovered in Russia’s Ural Mountains in the 1830s, it’s now found in Sri Lanka, East Africa, and Brazil, but fine material is exceptionally rare and valuable.
Mineral: Chrysoberyl;
Chemistry: BeAl2O4;
Color: Bluish green in daylight, purplish red in incandescent light;
Refractive index: 1.746 to 1.755;
Birefringence: 0.008 to 0.010;
Specific gravity: 3.73;
Mohs harness: 8.5;
COLOR: Fine alexandrite is green to bluish green in daylight and red to purplish red in incandescent light;
CLARITY: Good quality alexandrite has few inclusions. Rarely, needle-like inclusions create a cat’s-eye;
CUT: Alexandrite is most often available in mixed cuts. Its rarity means it is often cut to save weight;
CARAT WEIGHT: Most cut gems weigh less than one carat. Larger, higher-quality gems rise in price dramatically;
JUNE BIRTHSTONES – MOONSTONE A ghostly sheen moves under the surface of this feldspar, like moonlight glowing in water. 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.
Mineral: Feldspar;
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 harness: 6.0 to 6.5;
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~25.jpg

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