Mineralpedia Details for Pentahydroborite
Name is actually a misnomer for the composition which was originally described as having five (penta) water molecules per each formula unit. A rare mineral found only in Russia, Serbia, Japan, and possibly Kazakhstan. Pentahydoborite occurs as a mineral in boron bearing iron ore skarn and in volcanogenic sedimentary borate deposits. Pentahudroborite will fluoresce a purple-violet color under long-wave ultraviolet light.
Ref. Handbook of Mineralogy, Anthony et al (1995) and MSA at http://www.handbookofmineralogy.org/pdfs/pentahydroborite.pdf
Pentahydroborite from Fuka mine, Bitchu-cho, Okayama pref., Honsuh Island, Japan
Brown crystalline in matrix.