Tellurium

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Formula: Te
Native element, selenium group
Selen-tellurium is a selenium-bearing variety of tellurium.
Specific gravity: 6.1 to 6.3
Hardness: 2 to 2½
Streak: Grey
Colour: Tin-white
Melting point: 449.51°C
Boiling point: 988°C
Abundance in the earth’s crust: 1 part per billion by weight, 0.2 parts per billion by moles, which makes it one of the rarest stable solid elements (Wiki). Only iridium is rarer.
Common impurities: Se,Fe,Bi,S
Environments

Volcanic fumeroles
Hydrothermal environments

Tellurium is a hydrothermal vein mineral, which may be of both primary and secondary origin, and also a sublimate in volcanic fumaroles. Associated minerals include native gold, sylvanite, empressite, altaite, pyrite, galena, alabandite, baryte, quartz and carbonates (HOM).

Localities

At the Emperor mine, Vatukoula, Viti Levu, Fiji, tellurium occurs as a component of massive ore intimately mixed with sulphides, tellurides and gold, and also as fine crystals up to 4 cm long in quartz cavities (Minrec 39.4.300-301).

The type locality is the Mariahilf Mine, Faţa Băii, Zlatna, Alba, Romania.
Tellurium from the Mariahilf Mine - Image

At mines in the Cripple Creek mining district, Colorado, USA, tellurite in the oxidised zone with emmonsite and native gold (Minrec 36.2.181).

At the Tintic Mineral District, Utah, USA, although the district is well-known for its rich variety of tellurium minerals, native tellurium is quite rare. A specimen from the Trixie mine has been confirmed by alalysis and a sungle unanalysed specimen showing crystals of what is likely native tellurium has been collected from the North Star mine; it shows perfect cleavage and is directly associated with tellurite. The crystals are very crudely formed, and occur on matrix of quartz (MinRec 55.2.225).

Tellurium from Tintic - Image

Tellurium-bearing minerals include:

Alloys
törnroosite

Sulphides - the sulphide anion is S^2-
nagyágite
tetradymite

Sulphosalts - sulphide minerals with the general formula AmBnXp, where A represents a metal , B usually represents a semi-metal and X is sulphur or rarely selenium and/or tellurium
buckhornite
erniggliite
goldfieldite
stibiogoldfieldite

Selenides - the selenide anion is Se^2-
arsenoústalečite
gachingite
kitkaite
kawazulite

Tellurides - the telluride anion is Te^2-

Tellurobismuthides
kotulskite
moncheite
montbrayite

Oxides - the oxide anion is O^2-
kuranakhite
leisingite
tellurite
tewite
yafsoanite
zincospiroffite

Chlorides
telluroperite

Sulphates - the sulphate anion is (SO₄)^2-
adanite
bairdite
nabokoite

Thiosulphates - the thiosulphate anion is (S⁶⁺O₃S^2-)^2-, ie a sulphate anion with one O replaced by S
northstarite

Tellurates - Salts of telluric acid H₆Te⁶⁺O₆

Tellurites - the tellurite anion is (Te⁴⁺O₃)^2-

Chromates - the chromate anion is (CrO₄)^2-
chromschieffelinite

Phyllosilicates - (Si⁴⁺₂O₅)^2- groups
burckhardtite

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