Henmilite Locality: Fuka mine, Bitchu-cho (Bicchu-cho), Takahashi , Okayama Prefecture , Chugoku Region , Honshu Island , Japan ( Locality at mindat.org ) Size: 4.2 x 3.4 x 2.8 cm. An altered, lightweight, white, volcanic rock, hosts dozens of glassy and gemmy, deep purple-blue crystals, of henmilite, with crystals reaching .35 cm across. Henmilite, first discovered in Japan, is a very rare calcium, copper, boron hydroxide. This is a superb miniature of high quality from a remarkable find at the type locality, long thought unproductive, about 5-6 years ago. — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Henmilite
A rare blue-violet calcium-copper borate-hydroxide, usually as anhedral masses.
Intro adapted from Wikipedia (CC BY-SA).
Henmilite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula Ca₂Cu[B(OH)₄]₂(OH)₄.
It crystallizes in the triclinic crystal system (space group P-1).
Key properties: Mohs hardness 2.5; specific gravity 2.51; Pale violet to nearly white streak; Vitreous luster; optically biaxial.
IMA symbol Hen, IMA status: approved, named in 1981.
Very rare, in cavities in borate veins in contact-metasomatized limestone.
It is found associated with Pentahydroborite, tenorite, sillenite, bultfonteinite, cuspidine, thaumasite, brucite, calcite.
The mineral was named to honor Professor Kitinosuke Henmi (1919–1997), and his daughter Dr. Chiyoko Henmi (1949–), Department of Earth Science, Okayama University, Okayama, Japan.