Sanidine

Sanidine is the high temperature form of potassium feldspar (K,Na)(Si,Al)4O8. Sanidine most typically occurs in felsic volcanic rocks such as obsidian, rhyolite and trachyte. Sanidine crystallizes in the monoclinic crystal system. Orthoclase is a monoclinic polymorph stable at lower temperatures. At yet lower temperatures, microcline, a triclinic polymorph of potassium feldspar, is stable.
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(n.)
A variety of orthoclase feldspar common in certain eruptive rocks, as trachyte; -- called also glassy feldspar.
  

General Information:
 Chemical Formula:
(K,Na)(Si,Al)4O8
 Environment:
Acid volcanic rocks.
 Locality:
Common world wide occurrences.
 Name Origin:
From the Greek sanis - "little plate" and idos - "to see."
Physical Properties:
 Cleavage:
[001] Perfect, [010] Good
 Color:
colorless, white, gray, yellowish white, or reddish white.
 Density:
2.52
 Diaphaniety:
Transparent to translucent
 Habits:
Blocky - Crystal shape tends to be equant (e.g. feldspars)., Prismatic - Crystals Shaped like Slender Prisms (e.g. tourmaline)., Massive - Granular - Common texture observed in granit e and other igneous rock.
 Hardness:
6 - Orthoclase
 Luminescence:
Non-fluorescent.
 Luster:
Vitreous - Pearly
 Streak:
white
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B: (Kimia) sanidina
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