mineral

Black Star Diopside

Diopside (CaMgSi2O6) with Magnetite inclusions

Hardness: 5.5-6.5 (Mohs scale); Color: Black or dark brownish-black; Luster: Vitreous to greasy; Crystal structure: Monoclinic; Cleavage: Good in two directions at nearly 90 degrees; Specific gravity: 3.22–3.38; Asterism: 4-rayed star (cross).

Hardness: 5
Color: Black or dark brownish-black
Luster: Vitreous to greasy

Identified March 15, 2026More mineral →

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Physical properties

Formation & geological history

Formed in contact metamorphic rocks, skarns, and mafic or ultramafic igneous rocks. The 'star' effect is caused by tiny, needle-like inclusions of magnetite that align along the crystal planes. While the mineral diopside can be found in ancient Archaean formations, individual gem-quality specimens are typically excavated from Cenozoic era deposits.

Uses & applications

Primarily used in jewelry as cabochons to showcase the asterism (star effect). It is also valued by mineral collectors and used in limited industrial applications as a source of calcium and magnesium in ceramics and glass-making.

Geological facts

It is often called the 'Black Star of India' because the majority of high-quality specimens are mined there. Unlike Star Sapphires which typically have a 6-rayed star, Star Diopside features a distinct 4-rayed star, and one of the rays is usually slightly crooked rather than perfectly 90 degrees.

Field identification & locations

Identify in the field by looking for a black, glassy mineral in metamorphic or igneous contexts that reveals a 4-rayed star when viewed under a direct single light source (like the sun or a flashlight) when cut cabochon-style. Major sources include India (Namakkal), Russia, and Myanmar.

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