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Formula: Pb2Fe3+(Te6+O6)Cl
Tellurate
Crystal System: Trigonal
Specific gravity: 5.812 calculated for the empirical formula
Hardness: 2
Streak: Pale yellow
Colour: Yellow, tending to reddish orange
Environments
Müllerite is a relatively new mineral, approved in 2019.
Localities
There are three co-type localities, the Aga Mine, the Bird Nest drift and Bird Nest E3, all on Otto Mountain, Baker,
Soda Mountains, Silver Lake Mining District, San Bernardino county, California, USA. The Otto Mountain massif
contains the world’s most extensive assemblage of tellurium oxysalt (a
salt containing oxygen as well as a given anion) minerals, as well as being the type locality for 16 minerals
(as of Februry 2024): agaite,
andychristyite, bairdite,
chromschieffelinite,
eckhardite, fuettererite,
hagstromite, housleyite,
markcooperite, mojaveite,
müllerite, ottoite,
paratimroseite,
telluroperite, thorneite
and timroseite.
Although it has been found in most of the collecting areas on Otto Mountain, müllerite is relatively rare. It occurs
on recrystallised quartz fracture surfaces and in small vugs in association
with acanthite, cerussite,
hematite, khinite,
phosphohedyphane,
thorneite and timroseite.
Müllerite is a secondary oxidation zone mineral and is
presumed to have formed by oxidation of earlier formed tellurides, most
likely hessite, with
chalcopyrite and galena.
Müllerite occurs as hexagonal tablets and thin plates up to 0.2 mm across, but usually much smaller. Crystals
may occur as isolated tablets, intergrown ball-like clusters or scattered flakes. They are yellow, tending to reddish
orange, and have a pale yellow streak and subadamantine to greasy lustre
(CM 58.4.413-419).
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