Jun 4 2014
Alunite is a sulfate mineral, first discovered in Monti della Tolfa, Rome, in the 15th century. It is rarely found in the massive material cavities as distinct crystals.
It occurs as veins and replacement masses in rhyolite, trachyte, and other potassium rich volcanic rocks.
Properties of Alunite
The following are the key properties of Alunite:
- Cell Data
- Space Group: R3m or R3m (synthetic)
- a = 6.981(1)
- c = 17.331(4)
- Z = 3
- Crystal Data
- Hexagonal
- Point Group: 3 2/m or 3m
- Crystals: typically pseudocubic {0112} or tabular {0001} with flat vicinal rhombohedra, to 1cm
- Fibrous to columnar, porcelaneous, commonly granular to dense massive
- X-ray powder pattern: 2.89 (100), 2.99 (94), 2.293 (76), 1.926 (66), 4.96 (50), 1.503 (34), 5.77 (26)
- Chemical Composition
| Elements |
Content 1 |
Content 2 |
| SO3 |
38.34 |
38.66 |
| Al2O3 |
37.18 |
36.92 |
| H2O |
12.99 |
13.05 |
| K2O |
10.46 |
11.37 |
| P2O5 |
0.58 |
|
| Na2O |
0.33 |
|
| SiO2 |
0.22 |
|
| Total |
100.1 |
100 |
- Optical Properties
- Transparent to translucent
- Color: Colorless if pure; may be white, pale shades of gray, yellow, red, to reddish-brown
- Streak: White
- Luster: Vitreous, somewhat pearly on {0001}
- Optical Class: Uniaxial (+)
- ω = 1.572
- ε = 1.592
- Estimated Properties
| Electron density |
Bulk density (electron density) = 2.76 g/cm3
note: Specific gravity of Alunite = 2.75 g/cm3 |
| Photoelectric |
PEAlunite = 2.47 barns/electron
U = PEAlunite x ρElectron density = 6.80 barns/cm3 |
| Fermion index |
Fermion index = 0.001
Boson index = 0.99 |
Radioactivity
|
Alunite is barely radioactive
|
How to Identify Alunite
Alunite can be identified in white, gray, reddish-gray, and yellowish-white color. It has a transparent to translucent appearance. It is a non-fluorescent mineral, with a vitreous lustre, a white streak, and perfect cleavages. The fractures on the flat surfaces are uneven. Its crystals appear massive, granular, and fibrous.
The average density of alunite is 2.74 g/cm3, and its relative hardness ranges from 3.5 to 4.
Global Distribution
Alunite is distributed in the following places:
- Tolfa, northeast of Civitavecchia, Lazio, Italy
- Mukacheve (Muzijeva) and Beregavo, near Mukachevo, Ukraine
- Rodalquilar, Almeria Province, Spain
- D´ecazeville, Aveyron, France
- Marysvale, Ohio district, Piute Co. Utah, USA
- South River, Mineral Co. Red Mountain, Colorado
- Hinsdale Co. in the Rosita Hills
- Custer Co.
- Calico Peak porphyry, Rico district, Dolores Co.
- Meiklejohn Mountain, near Beatty, Nye Co. Nevada
- Lassen Volcanic National Park, Shasta Co. California
- Hickory’s Pond, near Placentia Bay, Newfoundland, Canada
- Bernborough, Hilton
- Mount Isa district, Queensland
- Bullah Delah, New South Wales, Australia
Occurrence of Alunite and Useful Mineral Association
Alunite is formed between 15°C (59°F) and 400°C (752°F) by the action of sulfate generated from pyrite or solfataric action on aluminous rocks, along with silicification and kaolinitization.
It is closely associated with quartz, gypsum, pyrite, diaspore, halloysite, and kaolinite.
References