Iodides, Natural

a mineral group of hydriodic acid salts, which very rarely occur with other minerals in the oxidation zone of silver, copper, and other nonferrous metal deposits. The known forms are miersite (Ag, Cu) I and cuproiodargyrite (Cu, Ag) I (crystallize in the isometric system, sphalerite structure); iodargyrite Agl (hexagonal system, wurtzite structure); and marshite Cul, for which both isometric (sphalerite structure) and hexagonal modifications exist.

The minerals come in varying shades of yellow, are either translucent or transparent, and range in luster from resinous to adamantine. The hardness on the mineralogical scale is 2.5 (1–1.5 for iodargyrite); the density in kg/m³ ranges from 5,504 (iodargyrite) to 5,640 (miersite). These minerals occur as separate small crystals, lamellar and squamose aggregates, and solid masses. Most of the natural iodides are known to exist in the oxidated ores of deposits in Chile, Mexico, the United States, and Australia. Iodargyrite has been discovered in Kazakhstan and Transbaikalia (USSR).