Formula: Ca2Cu[B(OH)4]2(OH)4
Henmilite is a rare blue calcium copper borate and was named after Professor Kitinosuke Henmi, and his daughter, Dr. Chiyoko Henmi form Okayama University. The Fuka Mine is the Type Locality, and in fact, is the only locality where henmilite has been found.
From Alfredo Petrov:
HENMILITE (henmi-ishi; henmi-seki)
- Okayama: Henmilite was originally found at Fuka in 1986 as scarce, bluish violet vitreous crystals to 0.2mm, and as crystal aggregates and small grains or anhedral masses, often little more than a purplish blue stain, associated with calcite (some as colourless “dogtooth” crystals), minor brucite, nifontovite and olshanskyite in small cavities in a pentahydroborite vein cutting a high-temperature pyrometasomatic marble. A second, and larger, find was in a Ca-borate vein averaging 10cm wide (max. to 2m wide), composed of takedaite, nifontovite, olshanskyite, sibirskite, parasibirskite, henmilite and pentahydroborite. Richer specimens, with deep blue henmilite crystals to 3mm, came out in 1992 from vugs in a calcite vein cutting gehlenite-spurrite skarn, with sillenite, kusachiite, bakerite, tenorite, bultfonteinite, apophyllite, cuspidine and thaumasite. Exceptional crystals were found again in 2000. An extraordinary 4m pocket yielding thousands of top-quality specimens was worked in mid-2002 (first appearing in public at the Fall 2002 Kyoto show). The largest known measuring 12mm(!), but they are normally much smaller, and even specimens with 5mm crystals are prized by collectors.
Above: Henmilite, Fuka mine, Fuka, Bitchū, Takahashi City, Okayama Prefecture, Japan. Tokyo Science and Nature Museum specimen.
