Hokkaidoite in Opal from Shikaribetsu Lake, Japan

Contributed by: FMS Admin
minID: C1E-HGF
Date: May 11th, 2026
Locality: Shikaribetsu Lake, Shikaoi (Shikaoi-Ch?), Kato District, Tokachi Subprefecture, Hokkaid? Prefecture, Japan (See on Mindat)
Size: 38 x 7 x 50 mm

Description:
Very nice, recently acquired specimen consisting of very brightly fluorescing hokkaidoite, in opal, from the Shikaribetsu Lake, Shikaoi, Kato District, Tokachi Subprefecture, Hokkaid? Prefecture, Japan.

Hokkaidoite is a very rare mineral, discovered recently in Japan and approved as a new mineral species in 2023. It is one of the very few mineral species that are actually organic minerals; it's a polycyclic aromatic hydrocarbon (C₂₂H₁₂). It fluoresces a very bright yellow, yellowish-green or green color under all UV wavelengths, and sometimes even fluoresces under strong blue light sources (I use a cheap 450 nm flashlight for my photos).

The opal in which it occurs generally reacts to blue light too. The opal typically fluoresces in various shades of blue, yellow and orange under all UV wavelengths. The response of the opal is rather identical under all wavelengths, showing only subtle variations; the blue intensifies slightly under shorter UV wavelengths, and the orange areas fluoresce a bit brighter under longwave. The opal shows phosphorescence after exposure to any UV wavelengths.

In the first picture of the gallery below, the specimen is shown fluorescing under longwave UV; in the next pictures, it is shown, respectively, under midwave UV LEDs (310 nm), shortwave UV LEDs (255 nm), blue light LED (450 nm). Then phosphorescence upon exposure to longwave, midwave and shortwave UV are shown, in this order. Lastly, the specimen is shown in 6500K white light.

Originally posted by Frédéric Messier Leroux on Nature's Rainbows in 2024.