Hydrobasaluminite
Hydrobasaluminite is an IMA-recognized mineral species in the sulfate class, with the chemical formula Al₄(SO₄)(OH)₁₀·15H₂O.
It crystallizes in the monoclinic crystal system.
Key properties: specific gravity 1.86; optically biaxial.
IMA symbol Hba, grandfathered status — known before the IMA’s founding, named in 1948.
Infilling vertical fissures in the weathering zone of siderite–chamosite ironstones (Irchester, England); in cave passages in argillaceous dolostone by the reaction of sulfuric acid with kaolinite (Cottonwood Cave, New Mexico, USA).
It is found associated with Basaluminite, gypsum, aragonite, halloysite, gibbsite, allophane, “limonite” (Irchester, England); gibbsite, amorphous silica (New Mexico, USA).
As the hydrated analog of basaluminite.