Ishikawaite
Ishikawaite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula (U,Fe,Y)NbO₄.
It crystallizes in the monoclinic crystal system. It is a member of the Samarskite structural group.
Key properties: Mohs hardness 5–6; specific gravity 6.2–6.4; Dark brown to black streak; Waxy, resinous to vitreous luster; optically isotropic.
IMA symbol Ikw, grandfathered status — known before the IMA’s founding, named in 1922.
Found in pegmatite, and alluvium (Ishikawa district, Japan); as micro-inclusions in vitrophyre clasts in highly differentiated, rare-element rich, pyroclastic rhyolites (Honeycomb Hills, USA).
It is found associated with Samarskite, ferrocolumbite (Ishikawa district, Japan).
The name refers to the occurrence in the Ishikawa district, Japan.