Brown acicular and platy crystals of the very rare borate magnesiohulsite from the type locality and only one of the three known localities worldwide (Qiliping Deposit, Changning County, Hengyang, Hunan Province, China). Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY-SA 4.0
Magnesiohulsite
Magnesiohulsite is an IMA-recognized mineral species in the borate class, with the chemical formula Mg₂Fe³⁺O₂(BO₃).
It crystallizes in the monoclinic crystal system (space group P2/m). It is a member of the Hulsite structural group.
Key properties: Mohs hardness 6; specific gravity 4.18; Dark brown streak; Submetallic luster; optically biaxial.
IMA symbol Mhul, IMA status: approved, named in 1983.
Found in a magnesium skarn borate deposit at the contact between granite and calcite–dolomite rocks.
It is found associated with Szaibélyite, kotoite, fluoborite, stannian ludwigite, sakhaite, dolomite, calcite.
As the magnesium analog of hulsite.