Banded variety of the mineral chalcedony This article is about the mineral. For the Pokémon with a similar name, see Onix (Pokémon). For other uses, see Onyx (disambiguation). "Black Onyx" redirects here. For the 1984 video game, see The Black Onyx. Onyx General Category Oxide mineral Formula .mw-parser-output .nobold{font-weight:normal} (repeating unit) Silica (silicon dioxide, SiO 2 ) Crystal system Trigonal Identification Formula mass 60 g / mol Color Various Cleavage no cleavage Fracture Uneven, conchoidal Mohs scale hardness 6.5–7 Luster Vitreous, silky Streak White Diaphaneity Translucent Specific gravity 2.55–2.70 Optical properties Uniaxial/+ Refractive index 1.530 to 1.543 References [1] [2] Onyx primarily refers to the parallel banded variety of the silicate mineral chalcedony. Agate and onyx are both varieties of layered chalcedony that differ only in the form of the bands: agate has ...