Sep 26 2013
Eggletonite was named after Dr. Richard A. Eggleton (associated with the Australian National University, Canberra), and was discovered in 1984. This mineral belongs to the ganophyllite group.
Properties of Eggletonite
The following are the key properties of Eggletonite:
- Cell Data
- Space group: I2/a or Ia
- a = 5.554
- b = 13.72
- c = 25.00
- β = 93:95°
- Z = 2
- Crystal Data
- Monoclinic
- Point group: 2/m or m
- Crystals display a pseudohexagonal cross section, elongated along [100], with {011} and {001} common
- As clusters of divergent sprays of radiating acicular prisms, to 2 cm
- Twinning: On {001}
- X-ray powder pattern: 12.4 (100), 3.13 (30), 2.691 (25), 2.600 (20), 2.462 (20), 3.45 (15), 2.854 (15)
- Chemical Composition
| Elements |
Content 1 |
| SiO2 |
41.5 |
| MnO |
31.4 |
| H2O |
[11.4] |
| Al2O3 |
7.6 |
| FeO |
3 |
| Na2O |
1.7 |
| CaO |
1.5 |
| K2O |
1.3 |
| ZnO |
0.2 |
| MgO |
0.4 |
| Total |
[100.0] |
- Optical Properties
- Optical class: Biaxial (-)
- Pleochroism: Very weak; X = pale brown to colorless; Z = pale yellow-brown
- Orientation: Z = b; X ≃ c'; Y ≃ a
- Dispersion: r < v; weak.
- Absorption: Z ≃ Y > X
- α = 1.566(2)
- β = 1.606(2)
- γ = 1.606(2)
- 2V(measurement) = 9(3)°
- Estimated Properties
| Electron density |
Bulk density (electron density) = 2.73 gm/cm3
note: Specific gravity of Eggletonite = 2.76 gm/cm3 |
| Fermion index |
Fermion Index = 0.0092304868
Boson Index = 0.9907695132 |
| Photoelectric |
PEEggletonite = 7.73 barns/electron
U = PEEggletonite x ρElectron Density = 21.13 barns/cm3 |
|
Radioactivity
|
Eggletonite is not radioactive. |
How to Identify Eggletonite
Eggletonite can be identified in the field by its golden brown-color and perfect cleavage. It has a glassy lustre with a light brown streak. The mineral has a brittle fracture and occurs as needle-like crystals that are shaped like thin prisms. The crystals radiate from a center without producing stellar patterns. The density of Eggletonite is 2.76 gm/cm3 with a hardness of 3 to 4 between calcite and fluorite.
Global Distribution
Eggletonite can be found in the following locations:
USA - Big Rock quarry, Granite Mountain, near Little Rock, Pulaski Co., Arkansas
Japan - Shiromaru mine (Hakumaru mine), Honshu Island.
Occurrence of Eggletonite and Useful Mineral Association
Eggletonite occurs in miarolitic pockets in nepheline syenite pegmatite. It is often associated with minerals such as natrolite, albite, kupletskite, apophyllite, and pyrophanite.
References