Mineral Guide · Mineral
Cafeosite is a rare meteoritic calcium iron oxysulfide and a redox indicator of alteration in carbonaceous meteorites.
Cafeosite is a rare meteoritic calcium iron oxysulfide and a redox indicator of alteration in carbonaceous meteorites.
The reference formula is Ca4Fe2+3Fe3+2□O6S4. Cafeosite belongs to the sulfides and crystallises in the orthorhombic system. The orthorhombic structure contains both ferrous and ferric iron plus a structural vacancy. Natural grains are very small, so the species is primarily of scientific and reference interest rather than a conventional hand-specimen mineral.
Typical colours include dark grey to black in reflected light. For small or complex mineral species, crystal size, transparency, lustre and matrix association are often more diagnostic than colour alone.
Cafeosite forms in or is associated with alteration of carbonaceous chondrites and highly reducing meteoritic environments. Important documented localities include Dhofar 225 meteorite from Oman, the type occurrence. A precise mine or geological setting is preferable to a broad country label when it is known.
Cafeosite is best treated as a labelled reference or collector specimen. Protect fragile crystals from impact and humidity changes. Arsenic-, cadmium-, lead-, thorium- and selenium-bearing minerals should not be cut, ground or used in jewellery; wash hands after handling and keep them away from food and children.
Reviewed by NotOnlyRocks Editorial Team
Last reviewed: 21 August 2026
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