Mineral - Phlogopite
Phlogopite
Chemical Properties
Mineral Class
Silicates
Toxicity
none
Formula
KMg₃[AlSi₃O₁₀|(F,OH)₂]
Unit Cell
a=5.31 b=9.19 c=10.16 β=100° Z=2
Physical Properties
Hardness
2 - 3
Streak
white
Density
Normal (2-3,5)
Cleavage
Perfect after {0001}
Fracture
smooth
Tenacity
Elastic-flexible
Optical Properties
Color
browngrayyellow
Birefringence
0.045
Luster
Vitreous,
Pearly
Transparency
translucent,
transparent
Pleochroism
Braun-Rot-Gelb
Geomineralogical Properties
Crystal System
monoclinic
Point Group
monoclinic-prismatic - 2/m
Space Group
C2/m (12)
Habit
leafy, book-shaped, prismatic, tabular
Formation
(1) Igneous, formed by crystallization from ultrabasic to intermediate melts in the presence of fluoride and hydroxide ions.
(2) Metamorphic, formed by the reaction of dolomite with quartz or potassium feldspar in magnesium-rich carbonate rocks under contact metamorphic conditions (metasomatism).
Paragenesis
Twinning
Stacked contact twins after {0001}
Rarity
Common
Synonyms
Phlogopite
Composition
Elements
Mass
SiO₂
42.00
TiO₂
0.22
Al₂O₃
12.70
FeO
0.25
MnO
0.08
NiO
0.02
ZnO
0.01
MgO
28.60
CaO
0.04
BaO
1.70
Li₂O
0.01
Na₂O
1.19
K₂O
8.46
Rb₂O
0.01
F
5.85
H₂O
1.51
O=F₂
2.46
New Jersey (Dana 1895)
Groups and Members
Mica-Group