May 10 2013
Tephroite is a non-metallic silicate mineral that was first described in 1823 from Franklin and Sparta, New Jersey, USA. It is a member of olivine group of minerals. The mineral named after the Greek word tephros, which means ash color.
Properties of Tephroite
The following are the key properties of Tephroite:
- Cell Data
- Space Group: Pbnm
- a = 4.86-4.90
- b = 10.59-10.62
- c = 6.22-6.25
- Z = 4
- Crystal Data
- Orthorhombic
- Point Group: 2/m 2/m 2/m
- Crystals typically short, prismatic, to 4 cm, or anhedral, equidimensional. Commonly in disseminated grains, compact, or massive
- Twinning: {011}, not common
- X-ray Powder Pattern: 2.560 (100), 2.867 (90), 1.814 (72), 2.607 (67), 3.627 (50), 1.565 (33), 2.695 (30)
- Chemical Composition
| Elements |
Content 1 |
Content 2 |
| MnO |
65.23 |
70.25 |
| MnO |
65.23 |
70.25 |
| SiO2 |
29.27 |
29.75 |
| CaO |
2.32 |
- |
| MgO |
1.98 |
- |
| FeO |
1.20 |
- |
| Total |
100.00 |
100.00 |
- Optical Properties
- Optical Class: Biaxial (-)
- Pleochroism: None or weak
- X = brownish red
- Y = reddish;
- Z = greenish blue
- Orientation: X = b; Y = c; Z = a
- Dispersion: r > v
- α = 1.770-1.788
- β = 1.807-1.810
- γ = 1.817-1.825
- 2V(meas.) = 60°-70°
- Estimated Properties
| Electron density |
Bulk density (electron density)=4.04 g/cm3
note: Specific gravity of Tephroite =4.25 g/cm3 |
| Photoelectric |
PETephroite = 14.67 barns/electron
U= PETephroite x ρElectron density= 59.28 barns/cm3 |
| Fermion index |
Fermion index = 0.0066
Boson index = 0.9933 |
Radioactivity
|
Tephroite is not radioactive
|
How to Identify Tephroite
Tephroite occurs in reddish brown, red, bluish green, olive green or gray color. It is non-fluorescent, and has transparent to translucent appearance, vitreous luster, nonmagnetic properties and gray streak. It can be formed as granular, prismatic or anhedral to subhedral crystals. It has indistinct cleavage and brittle fractures that produces small, conchoidal fragments. The average density of tephroite is 4.25 g/cm3, and its relative hardness is 6.5.
Global Distribution
Tephroite is distributed in the following places:
- Franklin and Sterling Hill, Ogdensburg, Sussex Co., New Jersey
- Bald Knob, near Sparta, Alleghany Co., North Carolina
- Sunnyside mine, San Juan Co., Colorado
- Buritirama, Piaui, Brazil
- Harstigen mine, near Persberg
- Langban, Varmland
- Sjao mine, near Grythyttan, Orebro, Sweden
- Benallt mine, near Rhiw, Lleyn Peninsula, Gwennyd, Wales
- Meldon quarry, Okehampton, Devon, and the Treburland mine, Altarnun, Cornwall, England
- Val Malenco, Lombardy, Italy
- Bonneval-sur-Arc, Haute-Maurienne, Isµere, France
- Wessels mine, near Kuruman, Cape Province, South Africa
- Kaso mine, Totigi Prefecture, and the Noda-Tamagawa mine, Iwate Prefecture, Japan
- Broken Hill and Tamworth, New South Wales, Australia
- Clark Peninsula, Wilkes Land, Antarctica.
Occurrence of Tephroite and Useful Mineral Association
Tephroite occurs in metamorphosed manganese-rich sediments and Fe-Mn ore deposits. It is closely associated with alleghanyite, banalsite, calcite, glaucochroite, manganocalcite, bustamite, gageite, diopside, jacobsite, rhodonite, franklinite, willemite and zincite.
References