Tephroite is a non-metallic manganese

Manganese

Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...

 silicate mineral with the formula, Mn

Manganese

Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...

₂Si

Silicon

Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...

O

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

₄.

It was first described for an occurrence at the Sterling Hill Mine and Franklin, New Jersey

Franklin, New Jersey

Franklin is a Borough in Sussex County, New Jersey, United States. As of the 2010 United States Census, the borough population was 5,045.Franklin, known as the "Fluorescent Mineral Capital of the World," is located over a rich ore body containing more than 150 minerals, many of them fluorescent and...

, USA. It occurs in iron-manganese ore deposits and their related skarn

Skarn

Skarn is an old Swedish mining term originally used to describe a type of silicate gangue, or waste rock, associated with iron-ore bearing sulfide deposits apparently replacing Archean age limestones in Sweden's Persberg mining district. In modern usage the term "skarn" has been expanded to refer...

s. It also occurs in metamorphosed

Metamorphism

Metamorphism is the solid-state recrystallization of pre-existing rocks due to changes in physical and chemical conditions, primarily heat, pressure, and the introduction of chemically active fluids. Mineralogical, chemical and crystallographic changes can occur during this process...

 manganese-rich sediments. It occurs in association with: zincite

Zincite

Zincite is the mineral form of zinc oxide . Its crystal form is rare in nature; a notable exception to this is at the Franklin and Sterling Hill Mines in New Jersey, an area also famed for its many fluorescent minerals. It has a hexagonal crystal structure and a color that depends on the presence...

, willemite

Willemite

Willemite is a zinc silicate mineral and a minor ore of zinc. It is highly fluorescent under shortwave ultraviolet light.It occurs in all different colors in daylight, in fibrous masses, solid brown masses , and apple green gemmy masses.It was discovered in 1830 and named after William I of the...

, franklinite

Franklinite

Franklinite is a mineral with formula ZnFe2O4. It is associated with the Franklin Mine and Sterling Hill Mines in New Jersey.-See also:* Spinel* Classification of minerals* List of minerals-References:*...

, rhodonite

Rhodonite

Rhodonite is a manganese inosilicate, SiO3 and member of the pyroxenoid group of minerals, crystallizing in the triclinic system...

, jacobsite

Jacobsite

Jacobsite is a manganese iron oxide mineral. It is in the spinel group and forms a solid solution series with magnetite. The chemical formula is MnFe2O4 or with oxidation states and substitutions:2O4....

, diopside

Diopside

Diopside is a monoclinic pyroxene mineral with composition MgCaSi2O6. It forms complete solid solution series with hedenbergite and augite, and partial solid solutions with orthopyroxene and pigeonite. It forms variably colored, but typically dull green crystals in the monoclinic prismatic class...

, gageite, bustamite

Bustamite

Bustamite is an calcium manganese inosilicate and a member of the wollastonite group. Magnesium, zinc and iron are common impurities substituting for manganese. It is a polymorph of johannsenite, with bustamite as the high-temperature form of CaMnSi2O6 and johannsenite as the low temperature form...

, manganocalcite, glaucochroite

Glaucochroite

Glaucochroite is a calcium manganese nesosilicate mineral with formula: CaMnSiO4. It occurs in metamorphosed limestones.It was first described in 1899 in Franklin Furnace, Sussex County, New Jersey.- References :* * *...

, calcite

Calcite

Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate . The other polymorphs are the minerals aragonite and vaterite. Aragonite will change to calcite at 380-470°C, and vaterite is even less stable.-Properties:...

, banalsite

Banalsite

Banalsite is a rare barium, sodium aluminium silicate mineral with formula: BaNa2Al4Si4O16. Banalsite is a tectosilicate of the feldspar group.Banalsite and its strontium analogue, stronalsite , constitute a complete solid solution series...

 and alleghanyite

Alleghanyite

Alleghanyite is a moderately rare humite mineral with formula Mn522, belonging to the nesosilicates class. In general its occurrences are related with metamorphic manganese deposits. The mineral is named after Alleghany County, North Carolina, USA....

. It can also be found in England

England

England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...

 and Sweden

Sweden

Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....

.

Tephroite has a hardness of 6 and a specific gravity

Specific gravity

Specific gravity is the ratio of the density of a substance to the density of a reference substance. Apparent specific gravity is the ratio of the weight of a volume of the substance to the weight of an equal volume of the reference substance. The reference substance is nearly always water for...

 of approximately 4.1, which is heavy for non-metallic minerals. Its name comes from the Greek tephros, "ash gray", for its color. It can also be found olive-green, greenish-blue, pink, or brown.