Greenish black microcrystals of nagashimalite in a small matrix of rhodonite from the TL in Japan (Mogurazawa Mine, Kiryuu City, Gunma Prefecture, Honshu Island, Japan). Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY-SA 4.0
Nagashimalite
Nagashimalite is an IMA-recognized mineral species in the silicate class, with the chemical formula Ba₄(V³⁺,Ti)₄(O,OH)₂[B₂Si₈O₂₇]Cl.
It crystallizes in the orthorhombic crystal system (space group Pmmn).
Key properties: Mohs hardness 6; specific gravity 4.08; Green streak; Submetallic to vitreous luster; optically biaxial.
IMA symbol Ngs, IMA status: approved, named in 1977.
Found in fissures cutting massive rhodonite ore in a bedded manganese deposit.
It is found associated with Rhodochrosite, rhodonite, barite, barian roscoelite, alabandite, digenite, bornite, tetrahedrite.
The name refers to pioneer Japanese amateur mineralogist, Otokichi Nagashima (1890–1969).