Mineral - Microcline
Microcline
Chemical Properties
Mineral Class
Silicates
Toxicity
none
Formula
K[AlSi₃O₈]
Unit Cell
a=8.58 b=12.96 c=7.21 α=91° β=116° γ=88° Z=4
Physical Properties
Hardness
6 - 6.5
Streak
white
Density
Normal (2-3,5)
Cleavage
Perfect after {001}, distinct after {010}
Fracture
uneven
Tenacity
Brittle
Optical Properties
Color
whitegrayredgreenbluecolorless
Birefringence
0.010
Luster
Vitreous,
Pearly
Transparency
translucent,
opaque
Pleochroism
Geomineralogical Properties
Crystal System
triclinic
Point Group
triclinic-pinacoidal - 1
Space Group
P 1 (2)
Habit
blocky, coarse, prismatic, tabular
Formation
(1) Magmatic, formed by slow cooling and crystallization from acidic to intermediate melts (especially in pegmatites) at temperatures below the monoclinic-triclinal stability point (approx. 450–500 °C)
(2) Metamorphic, formed by recrystallization or metasomatic processes in the amphibolite to granulite facies, as well as by the prolonged thermal ordering (Al/Si ordering) of orthoclase during cooling.
Paragenesis
Twinning
Contact twins after {001} - Manebach law
Rarity
Very common
Synonyms
Microcline
Composition
Elements
Mass
SiO₂
64.46
Al₂O₃
18.55
Fe₂O₃
0.14
CaO
0.17
Na₂O
0.49
K₂O
16.07
H₂O
0.06
Sweden (Dana 1895)
Groups and Members
Feldspar-Supergroup
Alkali-Feldspar-Group
K-Feldspar-Subgroup