Nagyágite

Formula: Pb₁₃Au₂Sb₃Te₆S₁₆

Origin of name: after locality Nagyag, Transylvania, Romania

Crystal system: orthorhombic

Crystal class: 2/m 2/m 2/m

Twinning: crossed lamellar

Unit cell: a = 8.34 Å, b = 30.2 Å, c = 8.29 Å

Colour: blackish lead-gray

Diaphaneity: 

Luster: metallic

Habit: crystals tabular, thin, striated, massive, granular or foliated

Hardness: 1 to 1.5

Specific gravity: 7.45 to 7.55

Cleavage: 1; {010} perfect

Tenacity: somewhat malleable, laminae

Streak: blackish lead-gray

Synonyms/varieties:

Comments: composition can vary from Pb₅Au(Sb,Bi)Te₂S₆ to Pb₅AuSbTe₃S₆, there may be an As analogue as well