Mineral - Allophane
Allophane
Chemical Properties
Mineral Class
Silicates
Toxicity
none
Formula
(Al₂O₃)(SiO₂)₂ · 3H₂O
Unit Cell
Physical Properties
Hardness
3
Streak
white
Density
Normal (2-3,5)
Cleavage
Fracture
conchoidal
Tenacity
Brittle
Optical Properties
Color
whitegraygreenblue
Birefringence
Luster
Vitreous,
Greasy
Transparency
translucent,
opaque
Pleochroism
Geomineralogical Properties
Crystal System
amorphous
Point Group
Space Group
Habit
spherical, stalactitic, grape-shaped
Formation
Secondary, through hydrothermal alteration of plutonites; also sedimentary
Paragenesis
Twinning
Rarity
Common
Synonyms
Allophane
Composition
Elements
Mass
SiO₂
28.31
TiO₂
0.40
Al₂O₃
34.41
Fe₂O₃
0.56
MgO
0.08
CaO
0.01
Na₂O
1.91
K₂O
0.29
H₂O
33.80
Japan (Kitagawa 1974)
Name and first discovery : Named after the Greek words "allos" for "other" and "phaenesthai" for "to appear," due to its similarity to certain copper minerals, allophane was first discovered near Gräfenthal in Thuringia and described in 1816 by the German mineralogists/chemists J.F.L. Hausmann and F. Stromeyer.
Chemistry :
Synonyms : Elhuyarite, Ilbaite, Riemannite
Varieties : Cupro-Allophan, Ferriallophane, Plumballophan, Phosphate-Allophan
literature
Kitagawa, Y. (1974). Dehydration of allophane and lts structural formula. American Mineralogist: Journal of Earth and Planetary Materials , 59 (9-10), 1094-1098.