Mineral - Cassiterite
Cassiterite
Chemical Properties
Mineral Class
Oxides and Hydrxides
Toxicity
none
Formula
SnO₂
Unit Cell
a=4.74 c=3.19 Z=2
Physical Properties
Hardness
6 - 7
Streak
white
Density
Very Heavy (>6)
Cleavage
Imperfect after {100}, indistinct after {110}
Fracture
uneven
Tenacity
Brittle
Optical Properties
Color
blackbrowngraygreen
Birefringence
0.103
Luster
Greasy,
Adamantine
Transparency
translucent,
opaque
Pleochroism
Geomineralogical Properties
Crystal System
tetragonal
Point Group
ditetragonal-dipyramidal - 4/m 2/m 2/m
Space Group
P4 2 /mnm (136)
Habit
blocky, dipyramidal, acicular, prismatic, tabular, Tetrahedron, barrel-shaped
Formation
(1) Primarily magmatic through crystallization from highly fractionated, acidic residual melts in granite pegmatites. (2) Hydrothermal-pneumatolytic in greisens and quartz veins through impregnation of boron- and fluorine-rich fluid phases in the perimagmatic zone of tin granites. (3) Metasomatic in skarn deposits through the interaction of metal-bearing fluids with carbonate country rock.
Paragenesis
Twinning
Contact and rotational twins after {101}
Rarity
Common
Synonyms
Cassiterite, Tin Spar, Tinstone
Composition
Elements
Mass
SiO₂
0.18
SnO₂
99.26
England (Palache et al. 1952)
Groups and Members
Rutile-Group