1.4 x 0.8 x 0.5 cm. Sulfoborite is a rare compound borate found in only four salt deposits in the world. Specimens are rare from any locale. Part of the orthorhombic prism is water-clear, colorless with the other part being translucent tan. From Inder B deposit and salt dome, Atyrau, Atyrau Province, Kazakhstan — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Sulfoborite
Sulfoborite is an IMA-recognized mineral species in the sulfate class, with the chemical formula Mg₃[B(OH)₄]₂(SO₄)(OH,F)₂.
It crystallizes in the orthorhombic crystal system (space group Pnma).
Key properties: Mohs hardness 4–4.5; specific gravity 2.38–2.45; optically biaxial.
IMA symbol Sbo, grandfathered status — known before the IMA’s founding, named in 1893.
Occurs as an uncommon mineral in marine salt deposits.
It is found associated with Carnallite, anhydrite, boracite, celestine, kieserite (Westeregeln, Germany); polyhalite, kaliborite, aphthitalite, carnallite.
In allusion to sulfur and boron in the composition.