White massive aggregates of the rare mineral tobelite from the type locality in Japan: Ohgidani deposit (Ogidani; Ougidani), Tobe, Ehime, Shikoku Island, Japan. — Photo: David Hospital · CC BY-SA 4.0
Tobelite
Tobelite is an IMA-recognized mineral species in the silicate class, with the chemical formula (NH₄)Al₂(Si₃Al)O₁₀(OH)₂.
It crystallizes in the monoclinic crystal system (space group C2/c). It is a member of the Mica structural group.
Key properties: specific gravity 2.58–2.62; Silky luster; optically biaxial.
IMA symbol Tbl, IMA status: approved, named in 1981.
A hydrothermal alteration product of a biotite andesite dike (Tobe, Japan); in a hydrothermally altered rhyolite tuff (Horo, Japan).
It is found associated with Quartz (Tobe, Japan); quartz, ammonium-rich mica, pyrophyllite, diaspore, kaolinite, corundum, andalusite (Horo, Japan).
The name refers to the occurrence at Tobe, Japan.