From Mindat.Org Photo Of The Day; October 30, 2018:
Molybdite: MoO3
Locality: Main Crater, Iodake (Iwodake; Ioudake), Satsuma-Ioujima (Satsuma-Iwojima; Iou island), Mishima village, Kagoshima Prefecture, Nansei Archipelago, Kyushu Region, Japan
“Molybdite grown as a high-temperature fumarole sublimate as platy, rectangular crystals on a crumbly fine-grained matrix. The rock sample was found near a high-temperature fumarole at the eastern interior wall of Iōdake. When viewed with the naked eye, the crystals appear as tiny sparkling flakes with a metallic luster, at large magnification as in this photo micrograph they are transparent, but with adamantine luster. Crystal shape, striation, high refractive index, environment and associated molybdenum minerals match molybdite. The blue color does not match, but the crystals are allochromatic and probably colorless when pure: the crystal ends are dark blue. Less colored crystals of the same morphology and luster have been found on the same rock sample. Colorless crystals of this mineral from a different rock sample of the same provenance have been analyzed with single crystal XRD and have been found to be molybdite. Field of View: 1 x 1 mm. Collection: Amir C. Akhavan”