Jun 12 2014
Aenigmatite was named after the Greek word for riddle, as an allusion to its (formerly) uncertain chemical composition.
Properties of Aenigmatite
The following are the key properties of Aenigmatite:
- Cell Data
- Space group: P1
- a = 10.406(13)
- b = 10.813(14)
- c = 8.926(6)
- α = 104° 56(9)’
- β = 96°52(11)’
- γ = 125°19(6)’
- Z = 2
- Crystal Data
- Triclinic, pseudomonoclinic
- Point group: 1
- Poorly developed, prismatic, to 8cm
- As irregular segregations
- Twinning: By rotation ⊥ (011) or about [010] of the pseudomonoclinic cell
- Polysynthetic
- X-ray powder pattern: 8.09 (vs), 3.145 (vs), 2.706 (s), 2.547 (s), 2.937 (ms), 2.119 (ms), 2.414 (m)
- Chemical Composition
| Elements |
Content 1 |
Content 2 |
Content 3 |
| SiO2 |
39.62 |
38.3 |
41.84 |
| FeO |
33.92 |
40.2 |
41.70 |
| TiO2 |
9.66 |
8.37 |
9.27 |
| Na2O |
7.20 |
6.35 |
7.19 |
| Fe2O3 |
4.64 |
- |
- |
| MnO |
2.46 |
1.93 |
- |
| MgO |
1.65 |
0.82 |
- |
| Al2O3 |
0.64 |
2.56 |
- |
| CaO |
0.44 |
1.42 |
- |
| H2O+ |
0.05 |
- |
- |
| K2O |
0.04 |
0.02 |
- |
| Cl |
0.02 |
- |
- |
| Total |
100.34 |
99.97 |
100.00 |
- Optical Properties
- Optical class: Biaxial (+)
- Pleochroism: X = yellow-brown; Y = red-brown; Z = dark brown to black
- Orientation: Y = b; Z ^ c = 45°
- Dispersion: r < v , very strong
- α = 1.793-1.81; β = 1.804-1.82; γ = 1.87-1.90
- 2V(meas.) = 30°-50°
- Estimated Properties
| Electron density |
Bulk density (electron density) = 3.68 g/cm3
note: Specific gravity of Aenigmatite = 3.80 g/cm3. |
| Photoelectric |
PEAenigmatite = 11.27 barns/electron
U = PEAenigmatite x ρ electron density = 41.50 barns/cm3 |
| Fermion index |
Fermion index = 0.02
Boson index = 0.98 |
Radioactivity
|
Aenigmatite is not radioactive
|
How to Identify Aenigmatite
Aenigmatite can be identified in the field by its color variations, such as brown, and black. Its opaque form has perfect cleavage. This mineral has a sub-adamantine luster, with reddish-brown streak. The density of Aenigmatite is 3.74 to 3.85 g/cm3, with a hardness of 5 to 6 - between apatite and orthoclase.
Global Distribution
Aenigmatite is distributed in the following places:
- Greenland - At Naujakasik, near the Tunugdliarfik Fjord, and on the Kangerdluarssuk Plateau, in the Ilimaussaq intrusion; from Narssarssuk
- Russia - In the Khibiny and Lovozero massifs, Kola Peninsula
- USA - from Granite Mountain, near Little Rock, Pulaski Co. Arkansas, and Santa Rosa, Sonoma Co. California.
- Australia - From Warrumbungle volcano, Nandewar volcano, and the Mt. Warning complex, New South Wales; and the Peak Range Province, Queensland
- New Zealand - From Logan Point quarry, Dunedin volcano
- Norway - At Sandefjord
- Italy - From Cuddua Mida, Sicily
Occurrence of Aenigmatite and Useful Mineral Association
Aenigmatite occurs as a primary constituent in sodium-rich alkalic volcanics, pegmatites, and other silica-poor igneous rocks.
It is often associated with minerals such as aegirine, riebeckite, augite, fayalite, arfvedsonite, hedenbergite, and ilmenite.
References