montbrayite

{{Infobox mineral | name = Montbrayite | category = Sulfosalt minerals | boxwidth = | boxbgcolor = | image = Montbrayite.jpg | imagesize = 230px | caption = Montbrayite (Montbray, Quebec) | formula = (Au,Ag,Sb,Bi,Pb)23(Te,Sb,Bi,Pb)38 or | IMAsymbol= Mnb | molweight = | strunz = 2.DB.20 | system = Triclinic | class = Plumbo-telluride | symmetry = | color = cream, yellowish white, very light yellow | habit = small segregations, rarely exceeding 3-5 mm, crystals very rare | twinning = observed | cleavage = very good {110}, {011}, {111} | fracture = irregular to uneven, sub-conchoidal, the mineral is very fragile | tenacity = very brittle | mohs = 2.5 | luster = metallic | polish = | refractive = | opticalprop = | birefringence = | dispersion = | pleochroism = very weak | fluorescence= | absorption = | streak = | gravity = | density = 9.94 (measured) | melt = | fusibility = | diagnostic = | solubility = | diaphaneity = opaque | other = | references = }} Montbrayite (from a Canadian toponym) is a very rare mineral from among the gold tellurides, close to krennerite and calaverite, in composition it is a mixed polymetallic plumbo-telluride of gold with a variable formula, initially written as Au2Te3, or , but today having a much more complex form in the calculated form: . The color of montbrayite is cream, tin-white to pale yellow, the luster is metallic.

== Discovery history and name == The mineral was first identified in 1946 by M. A. Peacock and R. M. Thompson at the Canadian Robb Montbray deposit (Quebec). Almost immediately, it was analyzed and a description of montbrayite was published as a new gold telluride with the formula Au2Te3. The mineral was named after the location of its discovery, the typical Canadian Montbray deposit, which remained the only one for montbrayite for the next quarter of a century.