Sep 26 2013
Evansite is a secondary amorphous mineral occurring with allophane and limonite. This mineral was named after Brooke Evans, a British metallurgist from Birmingham, England who brought the first specimens from Hungary in 1855.
Properties of Evansite
The following are the key properties of Evansite:
- Cell Data
- Crystal Data
- Amorphous
- Point Group: n.d
- Commonly as reniform or botryoidal coatings; spherulitic or stalactitic, to 0.6 m, may show a concentric structure.
- X-ray powder pattern: Amorphous to X-rays.
- Chemical Composition
| Elements |
Content 1 |
Content 2 |
Content 3 |
| H2O |
39.95 |
41.27 |
42 |
| Al2O3 |
39.31 |
40.19 |
39.62 |
| P2O5 |
19.05 |
18.11 |
18.38 |
| insol. |
1.41 |
- |
- |
| Total |
99.72 |
99.57 |
100 |
- Optical Properties
- Optical Class: Isotropic may show birefringence up to 0.02
- n = 1.445–1.485.
- Estimated Properties
| Electron density |
Bulk density (electron density) = 2.02 g/cm3
note: Specific gravity of Evansite = 1.95 g/cm3 |
| Photoelectric |
PEEvansite = 1.11 barns/electron
U = PEEvansite x ρElectron density = 2.23 barns/cm3 |
| Fermion index |
Fermion index = 0.0003
Boson index = 0.9996 |
|
Radioactivity
|
Evansite is not radioactive. |
How to Identify Evansite
Evansite can be colorless or blue, white, green and yellow. This mineral has transparent to translucent appearance with white streaks and vitreous luster. It exhibits non-fluorescent and non-magnetic properties. The conchoidal fractures developed in brittle materials are characterized by smooth curving surfaces. The mineral can be observed in various forms like stalactitic, reniform and botryoidal. The relative hardness of evansite ranges from 3.5 to 4, and its average density is 1.95 g/cm3.
Global Distribution
Evansite is distributed in the following places:
- SIRK-Zeleznik (Vashegy), Slovakia
- Gross-Tresny; Litošice
- Alsô-Sajô, Romania
- Rosia Montan˘a (Verespatak), Romania
- Baia-de-Arie (Offenb´anya), Romania
- Epernay, Marne, France
- Campo Lameiro, Spain
- Teis, near Vigo, Spain
- Pontevedra Province
- santa Cruz de Olarde, Barcelona Province
- Richelle, near Vis´e, Belgium
- Yoredale Rocks, near Macclesfield, Cheshire
- Vatoinandry district, Madagascar
- Berlin and other caves, Transvaal, South Africa
- Zeehan and Dundas districts, Tasmania, Australia
- Columbiana and Coalville, Shelby Co., Alabama
- Wilson Springs, Garland Co., Arkansas
- Goldburg, Custer Co., Idaho
- Cueva de Cunday, Colombia
- Cueva de Urtany and Cueva de Aguapiras Caves, Venezuela.
Occurrence of Evansite and Useful Mineral Association
Evansite occurs in a graphite deposit (Gross-Tresny, Czech Republic), graphitic gneiss (Vatoinandry district, Madagascar), coal seams (Alabama, USA) and coating in caves, the phosphate derived from guano. It is closely associated with limonite, allophane and variscite.
References