Tephroite
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Tephroite was named in 1823 by Johann Friedrich August Breithaupt from Greek word tephros meaning ash-colored, alluding to the usual gray color of the mineral.

Discovered in 1823; IMA status: Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

Mn²⁺₂SiO₄

Manganese Silicate

Molecular Weight:

201.96 gm

Composition:

Manganese

54.41 %

Mn

70.25 %

MnO

Silicon

13.91 %

Si

29.75 %

SiO₂

Oxygen

31.69 %

O

100.00 %

100.00 %

= TOTAL OXIDE

Classification

Mineral Classification:

SILICATES (Germanates)

Strunz 8th Ed. ID:

8/A.04-30

Nickel-Strunz 10th Ed. ID:

9.AC.05

9 : SILICATES (Germanates)
A : Nesosilicates
C : Nesosilicates without additional anions; cations in octahedral [6] coordination

Related to:

Olivine Group. Fayalite-Tephroite Series. Forsterite-Tephroite Series. The Mn2+ analogue of Fayalite, Forsterite, and Calcio-Olivine.

Members of Group:

Olivine Group: Calcio-olivine, Fayalite, Forsterite, Claucochroite, Kirschsteinite, Laihunite, Liebenbergite, Monticellite, Olivine, Roepperite, (of Brush), Tephroite

Varieties:

None

Synonyms:

Mangan-Peridot, ICSD 100433, PDF 35-748

Crystal Data

Crystallography:

Orthorhombic - Dipyramidal

Crystal Habit:

Crystals typically short, prismatic, to 4 cm, or anhedral, equidimensional. Commonly in disseminated grains, compact, or massive.

Twinning:

{011}, not common

Physical Properties

Cleavage:

Distinct on {010}, imperfect on {001}

Fracture:

Uneven to conchoidal

Tenacity:

Brittle

Moh's Hardness:

6.0

Density:

3.87 - 4.12 (g/cm³)

Luminescence:

None. Often associated with fluorescent minerals such as Calcite and Willemite.

Radioactivity:

Not Radioactive

Optical Properties

Color:

Olive-green, bluish green, gray, flesh-red, reddish brown; pale green in thin section, may be colorless.

Transparency:

Transparent to translucent

Luster:

Vitreous to greasy

Refractive Index:

1.759 - 1.860  Biaxial ( - )

Birefringence:

0.101

Dispersion:

r > v

Pleochroism:

None or weak; X = brownish red; Y = reddish; Z = greenish blue

Occurances

Geological Setting:

In Fe-Mn ore deposits, related skarns, and metamorphosed manganese-rich sediments.

Common Associations:

Zincite, Willemite, Franklinite, Rhodonite, Jacobsite, Diopside, Gageite, Bustamite, Manganocalcite, Glaucochroite, Calcite, Banalsite, Alleghanyite

Common Impurities:

Fe, Zn, Ca, Mg

Type Locality:

Sterling Mine, Sterling Hill, Ogdensburg, Franklin Mining District, Sussex County, New Jersey, USA

Year Discovered:

1823

View mineral photos:

Tephroite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Tephroite is a manganese silicate mineral that is a member of the Olivine Group of minerals that includes Fayalite, Forsterite, Olivine and Tephroite. Tephroite forms a series with Fayalite. Tephroite is the manganese rich member of the series and Fayalite is the iron rich member. Tephroite is a contact metamorphic and hydrothermal replacement mineral. It is commonly ash gray but also is found in colors of olive-green, greenish-blue, pink or brown. The type locality for Tephroite is the famous Sterling Mine, Sterling Hill, Ogdensburg, Franklin Mining District, Sussex County, New Jersey, USA. The Sterling Mine and nearby Franklin Mines are well known for their mineral abundance and diversity. In the area of the Franklin and Sterling Hill mines, 357 types of minerals are known to occur; these make up approximately 10% of the minerals known to science. Thirty-five of these minerals have not been found anywhere else. Ninety-one of the minerals are fluorescent. Tephroite is not a fluorescent mineral but is ofter found associated with fluorescent minerals such as Bustamite, Calcite, Willemite and Zincite. Tephroite was named in 1823 by Johann Friedrich August Breithaupt from Greek word tephros meaning ash-colored, alluding to the usual gray color of the mineral.

Locations for Tephroite: In the USA, from Franklin and Sterling Hill, Ogdensburg, Sussex County, New Jersey; at Bald Knob, near Sparta, Alleghany County, North Carolina; and in the Sunnyside mine, San Juan County, Colorado. From Buritirama, Piaui, Brazil. In the Harstigen mine, near Persberg; at Långban, Värmland; and in the Sjö mine, near Grythyttan, Örebro, Sweden. From the Benallt mine, near Rhiw, Lleyn Peninsula, Gwennyd, Wales. In the Meldon quarry, Okehampton, Devon, and the Treburland mine, Altarnun, Cornwall, England. At Val Malenco, Lombardy, Italy. From Bonneval-sur-Arc, Haute-Maurienne, Isère, France. Large crystals from the Wessels mine, near Kuruman, Cape Province, South Africa. In the Kaso mine, Totigi Prefecture, and the Noda-Tamagawa mine, Iwate Prefecture, Japan. From Broken Hill and Tamworth, New South Wales, Australia. On the Clark Peninsula, Wilkes Land, Antarctica.
 

  
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