Difference between revisions of "Feldspar"
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Revision as of 13:21, 2 October 2006
|Chemical composition|| Potassium, sodium and calcium-aluminum silicates|
I. K-feldspar (KALSi308)
|Crystal system||Monoclinic - triclinic|
|Habit||Prismatic, often twinned|
|Cleavage||Good to perfect|
|Optic nature||Biaxial ±|
|Refractive index|| 1.52 - 1.53 (K-feldspar)|
1.528 - 1.588 (plagioclase)
|Birefringence|| 0.006 - 0.007 (K-feldspar)|
0.008 - 0.011 (plagioclase)
|Specific gravity|| 2.55 - 2,58 (K-feldspar)|
2.60 - 2.80 (plagioclase)
Feldspar is a group of minerals that are very important in rock formation, accounting for over half the earth's crust! There are a number of varieties that are used in jewelry. The most important are andesine, sunstone, amazonite, moonstone, and labradorite, the latter known for their phenomenal iridescence and adularescence. Amazonite was used by the ancient Egyptians for the carving of deities. The stone was considered a catalyst between the living and the gods. Moonstone was thought to drive away sleeplessness.