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Alunite
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Discovered in 1824; IMA status: Valid (pre-IMA; Grandfathered)
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Chemistry
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Chemical
Formula: |
KAl3(SO4)2(OH)6
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Potassium
Aluminum Sulfate Hydroxide |
Molecular
Weight: |
414.21 gm
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Composition: |
Potassium |
9.44 % |
K |
11.37 % |
K2O |
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Aluminum |
19.54 % |
Al |
36.92 % |
Al2O3 |
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Hydrogen |
1.46 % |
H |
13.05 % |
H2O |
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Sulfur |
15.48 % |
S |
38.66 % |
SO3 |
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Oxygen |
54.08 % |
O |
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100.00 % |
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100.00 % |
= TOTAL OXIDE |
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Classification
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Mineral
Classification: |
Sulfates
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Strunz 8th
Ed. ID:
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6/B.11-20
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Nickel-Strunz 10th
Ed. ID:
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7.BC.10
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7 : SULFATES (selenates, tellurates, chromates, molybdates,
wolframates) B : Sulfates (selenates, etc.) with additional anions, without
H2O
C : With medium-sized and large cations
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Related
to: |
Alunite Supergroup. Alunite
Subgroup. Natroalunite - Jarosite - Beaverite
Series.
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Members
of Group: |
Alunite Supergroup:
Beudantite Subgroup,
Crandallite Subgroup, Florencite Subgroup, Jarosite Subgroup.
Alunite
Subgroup: Alunite, Ammonioalunite,
Natroalunite.
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Varieties: |
None
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Synonyms: |
Aluminilite,
Alumstone, Calafatite, Ignatiewite, Kalioalunite, K-Alunite,
LÅ“wigite, Lowigite, LÅ“vigite, Newtonite
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Crystal
Data
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Crystallography:
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Trigonal
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Crystal
Habit:
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Crystals
typically pseudocubic or tabular with flat vicinal rhombohedra,
to 1 cm; fibrous to columnar, porcelaneous, commonly
granular to dense massive.
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Twinning:
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None
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Physical
Properties
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Cleavage: |
Perfect
on [0001]
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Fracture: |
Conchoidal
to Uneven
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Tenacity:
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Brittle
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Moh's
Hardness: |
3.5
- 4.0
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Density:
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2.60
- 2.90 (g/cm3)
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Luminescence:
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None |
Radioactivity:
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Barely
Detectable;
GRapi = 136.78 (Gamma Ray American Petroleum Institute Units)
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Other: |
Insoluble
in water.
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Optical
Properties
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Color: |
Colorless
if pure; may be White, pale shades of Gray, Yellow,
Red, to Reddish Brown from impurities.
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Transparency: |
Opaque,
Translucent, Transparent on thin edges |
Luster: |
Vitreous;
somewhat Pearly on [0001] |
Refractive
Index: |
1.572
- 1.592 Uniaxial ( + )
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Birefringence: |
0.0020
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Dispersion: |
None
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Pleochroism: |
None
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Other: |
Strongly
pyroelectric
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Occurances
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Geological
Setting: |
Formed
between 15º C and 400º C by the action of
sulfate, which may be generated from pyrite or solfataric
action, on aluminous rocks, commonly accompanied by
kaolinitization and silicification. |
Common
Associations: |
Diaspore,
Gypsum, Halloysite, Kaolinite, Pyrite, Quartz |
Common
Impurities: |
Na,
Fe |
Type
Locality: |
Allumiere Quarries, Allumiere, Rome Province, Latium,
Italy |
Year
Discovered: |
1824
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View
mineral photos: |
Alunite
Mineral Photos and Locations |
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Unusual Gem Categories
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Radioactive Gems
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More
Information
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Mindat.org
Webmineral.com
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Alunite,
also known as Alumstone, is a source of the chemical
known as alum and is a rock-forming mineral. Alunite forms from the action of sulfuric acids upon potassium rich
feldspars in a process called "alunitization".
Alunite
can easily be mistaken for Dolomite and Calcite.
Alunite is named from the Latin word alunit for Alum. Alum is a chemical compound, usually a hydrated double sulfate salt of aluminium.
Sources
of Alunite are Marysvale, Utah; Red Mountain, Custer County, Colorado;
Goldfield district,
Nevada, USA; and Tolfa, Italy.
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gems for sale:
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