mineral

Osumilite in Granite Matrix

(K,Na)(Fe,Mg)2(Al,Fe)3(Si,Al)12O30

Hardness: 5-6 Mohs. Color: Blue, black, dark brown, or olive green. Luster: Vitreous/Glassy. Crystal Structure: Hexagonal (Dihexagonal dipyramidal). Specific Gravity: 2.64.

Hardness: 5-6 Mohs
Color: Blue, black, dark brown, or olive green
Luster: Vitreous/Glassy

Identified March 2, 2026More mineral →

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Physical properties

Hardness: 5-6 Mohs. Color: Blue, black, dark brown, or olive green. Luster: Vitreous/Glassy. Crystal Structure: Hexagonal (Dihexagonal dipyramidal). Specific Gravity: 2.64.

Formation & geological history

Formed in high-temperature, low-pressure metamorphic rocks or as a primary mineral in felsic volcanic rocks and granitic pegmatites. This specimen likely originates from a contact metamorphic zone or a rare accessory occurence in an igneous body.

Uses & applications

Osumilite is primarily a collector's mineral due to its rarity. It has no major industrial uses but is highly valued by mineralogical museums and specialized systematic collectors.

Geological facts

Osumilite was first discovered in 1953 in the Osumi Province of Japan. It is part of the milarite group of silicate minerals and is often mistaken for cordierite due to its similar appearance and geological environment.

Field identification & locations

Identified in the field by its hexagonal crystal habit and association with quartz, feldspar, and biotite. Common locations include Japan, Germany (Eifel region), and Italy. Collectors look for the characteristic dark blue-grey translucent sheen.

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