Cadmoindite
Cadmoindite, from Kudriavy Volcano, Far Eastern Region, Russian Federation
General
Category	Sulfide mineral Thiospinel group Spinel structural group
Formula (repeating unit)	CdIn2S4
IMA symbol	Cad[1]
Strunz classification	2.DA.05
Crystal system	Cubic
Crystal class	Hexoctahedral (m3m) H-M symbol (4/m 3 2/m)
Space group	Fd3m
Unit cell	a = 10.81 Å; Z = 8
Identification
Formula mass	470.32 g/mol
Color	Black to dark brown
Crystal habit	Microscopic octahedral crystals
Fracture	Conchoidal
Luster	Adamantine
Diaphaneity	translucent
Optical properties	Isotropic
References	[2][3]

Cadmoindite (CdIn₂S₄) is a rare cadmium indium sulfide mineral discovered in Siberia around the vent of a high-temperature (450–600 °C) fumarole at the Kudriavy volcano, Iturup Island in the Kuril Islands. It has also been reported from the Kateřina Coal Mine in Bohemia, Czech Republic.^[3]

Crystal structure

CdIn₂S₄ exhibits the spinel structure, which can be described by a cubic unit cell with 8 tetrahedrally coordinated and 16 tetrahedrally coordinated cation sites. The distribution of Cd(II) and In(III) over the cation sites is difficult to elucidate from standard X-ray diffraction techniques because the two species are isoelectronic, but both Raman spectroscopy measurements on synthetic samples^[4] and density functional theory simulations^[5] indicate that about 20% of the tetrahedral sites are occupied by In(III) cations.

References