Mineral - Alunite
Alunite
Chemical Properties
Mineral Class
Sulphates
Toxicity
none
Formula
KAl₃[(OH)₆|(SO₄)₂]
Unit Cell
a=6.98 c=17.33 Z=3
Physical Properties
Hardness
3.5 - 4
Streak
white
Density
Normal (2-3,5)
Cleavage
Perfect after {001}
Fracture
conchoidal
Tenacity
Brittle
Optical Properties
Color
whitebrownredorangepink
Birefringence
0.020
Luster
Vitreous,
Pearly
Transparency
translucent,
opaque
Pleochroism
Geomineralogical Properties
Crystal System
trigonal
Point Group
ditrigonal-scalenohedral - 3 m
Space Group
R 3 m (166)
Habit
leafy, granular, Rhombohedron, tabular
Formation
Reaction of sulphate, from pyrite decomposition on aluminum-containing rocks
Paragenesis
Twinning
Rarity
Rather rare
Synonyms
Alunite
Composition
Elements
Mass
SO₃
38.34
P₂O₅
0.58
SiO₂
0.22
Al₂O₃
37.18
Na₂O
0.33
K₂O
10.46
H₂O
12.99
Utah (Palache et al. 1952)
Groups and Members
Alunite-Supergroup
Alunite-Group
Name and first discovery : Named after the Latin word "alumen" for "alum," due to the mineral's use in alum production. Alunite was first mined in the 15th century in Tolfa near Rome for alum production under the control of the Popes. In 1707, it was described by Jean-Claude Delamétherie as aluminilite, which was then shortened to alunite by François Sulpice Beudant in 1824.
Chemistry :
Synonyms : Aluminilite, Calafatite, Ignatiewit, Kalioalunit, Lœvigite, Lœwigit, Lowigite
Varieties :
Abbreviation : Alu
literature
Palache, C., Berman, H., & Frondel, C. (1952). Dana's system of mineralogy. Geologiska Föreningen i Stockholm Förhandlingar , 74 (2), 218-219.