Hokkaidoite and Opal-AN from Japan
Contributed by: Michael Crawford
Date: Aug 12th, 2025
Locality: Shikaribetsu Lake, Shikaoi (Shikaoi-Ch?), Kato District, Tokachi Subprefecture, Hokkaid? Prefecture, Japan (See on Mindat)
Description:
Greg Vella sent me two specimens that contain hokkaidoite (C22H12) and opal-AN from Shikaribetsu Lake, Hokkaido Prefecture, Japan. The specimens were cut from larger specimens that were analyzed with High Performance Liquid Chromatography (HPLC) to confirm the presence of hokkaidoite. The hokkaidoite occurs as small dendrites encased in opal-AN. The hokkaidoite occurs in the outer layer of the specimens indicated by REF-1 through REF-5 on the annotated image. The dendrites appear as yellow green specks in yellow opal when exposed to longwave UV illumination. The yellow green fluorescence is caused by the polycyclic aromatic hydrocarbon (PAH) structure of hokkaidoite. The PAH structure has a high number of conjugated double bonds that are easily excited by UV light.
Longwave emission spectra were measured at each location pointed out in the annotated image to look at the variability of the hokkaidoite emission. There are two signatures. One signature has peaks at 480 nm, 515 nm and 540 nm. The other signature is like the first signature, but it has peaks at 470 nm, 506 nm and 540 nm. There is a yellow fluorescent layer marked as REF-6. The emission spectrum of this yellow fluorescent layer is very different from the hokkaidoite bearing layers. It has a signature with three distinct peaks at 476 nm, 503 nm and 540 nm.
The specimens are 9 cm by 5.5 cm and 6 cm by 2 cm.
Summary of luminescence responses:
Hokkaidoite (Mindat) (RRUFF)
- Fluorescence under Longwave (365nm LED) UV light: Yellow
- Fluorescence under Longwave (365nm LED) UV light: Orange
- Fluorescence under Longwave (365nm LED) UV light: Blue