Jun 12 2014
Topics Covered
Introduction to Afghanite
Properties of Afghanite
How to Identify Afghanite
Global Distribution
Occurrence of Afghanite and Useful Mineral Association
References
Introduction to Afghanite
Chemical Formula - (Na,Ca,K)8(Si,Al)12O24(SO4,Cl,CO3)3• H2O
Afghanite was named after Afghanistan, the country where it was first discovered. It belongs to the cancrinite group.
Properties of Afghanite
The following are the key properties of afghanite:
- Cell Data
- Space group: P63/mmc, P63/mc, or P62c
- a = 12.77(3)
- c = 21.35(4)
- Z = 3
- Crystal Data
- Hexagonal
- Point group: 6/m 2/m 2/m, 6mm, 6 m2
- Stout to slender
- Thin tabular laths
- Rounded grains
- X-ray powder pattern: 3.688 (100), 3.298 (100), 4.82 (80), 3.997 (60), 2.865 (60), 2.130 (60), 1.792 (60)
- Chemical Composition
| Elements |
Content 1 |
Content 2 |
| SiO2 |
30.8 |
32.96 |
| Al2O3 |
25 |
25.45 |
| CaO |
16.5 |
11.98 |
| Na2O |
12.6 |
12.52 |
| SO3 |
8.5 |
10.82 |
| Cl |
4.6 |
3.98 |
| K2O |
2.7 |
3.07 |
| - O=Cl2 |
1.0 |
0.9 |
| H2O |
0.7 |
- |
| CO2 |
0.4 |
- |
| Total |
100.8 |
99.88 |
- Optical Properties
- Transparent
- Optical class: Uniaxial (+)
- ω = 1.523(2)
- ε = 1.529(2)
- Estimated Properties
| Electron density |
Bulk density (electron density) = 2.57 g/cm3
note: Specific gravity of afghanite = 2.60 g/cm3 |
| Photoelectric |
PEAfghanite = 3.25 barns/electron
U = PEAfghanite x ρ electron density = 8.37 barns/cm3 |
| Fermion index |
Fermion index = 0.0072
Boson index = 0.9927 |
Radioactivity
|
Afghanite is not radioactive
|
How to Identify Afghanite
Afghanite can be identified in the field by its blue color. It can also be colorless. Its transparent form has {1010} perfect cleavage. This mineral has a vitreous luster, with a white streak. The fracture on this mineral is conchoidal.
The density of Afghanite is 2.55 to 2.65 g/cm3, with a hardness of 5.5 to 6 - between a knife blade and orthoclase.
Global Distribution
Afghanite is distributed in the following places:
- Afghanistan - At Sar-e-Sang, Badakhshan Province
- Italy - At the Pitigliano quarry, near Grosseto, Tuscany; on Monte Somma, Campania; from Vetralla and Bassano, Latium
- Russia - In the Malaya Bystraya and Tultuy lazurite deposits, near Lake Baikal, and in other unspecified deposits in eastern Siberia
- Tajikistan - From Lyadzhuar-Darinsk, Pamir Mountains
- USA - In the Edwards mine, Edwards, St. Lawrence Co. New York
- Canada - At Lake Harbour, Baffn Island, Newfoundland
- Germany - Rhineland-Palatinate, Ettringen, Bellerberg volcano, Caspar quarry
Occurrence of Afghanite and Useful Mineral Association
Afghanite occurs in thin veinlets cutting lazurite crystals; in silicfied limestone xenoliths in pumice.
It is often associated with minerals such as sodalite, nepheline, lazurite, olivine, vesuvianite, calcite, diopside, pyrite, and phlogopite.
References