Mineral - Sanidine
Sanidine
Chemical Properties
Mineral Class
Silicates
Toxicity
none
Formula
K(AlSi₃O₈)
Unit Cell
a=8.60 b=13.04 c=7.17 β=116° Z=4
Physical Properties
Hardness
6
Streak
white
Density
Normal (2-3,5)
Cleavage
Perfect after {001}, distinct after {010}
Fracture
conchoidal,
uneven
Tenacity
Brittle
Optical Properties
Color
grayyellowcolorless
Birefringence
0.007
Luster
Vitreous,
Pearly
Transparency
translucent,
transparent
Pleochroism
Geomineralogical Properties
Crystal System
monoclinic
Point Group
monoclinic-prismatic - 2/m
Space Group
C2/m (12)
Habit
massive, prismatic, tabular
Formation
(1) Magmatic, as a primary crystallization phase in acidic to intermediate volcanic rocks (rhyolites, trachytes, phonolites)
(2) Metamorphic, under high-temperature, low-pressure conditions of the sanidinite facies (contact metamorphism).
(3) Post-magmatic-hydrothermal, formed by alteration processes or as spherulites in volcanic glasses.
Paragenesis
Twinning
Rarity
Common
Synonyms
Sanidine
Composition
Elements
Mass
SiO₂
64.79
Al₂O₃
18.50
K₂O
16.79
Canada (Dana 1895)
Groups and Members
Feldspar-Supergroup
Alkali-Feldspar-Group
K-Feldspar-Subgroup