Mineral Guide · Mineral

Galaxite

Galaxite is the manganese-rich spinel-group oxide, generally brown to black and found in manganese-rich metamorphic assemblages.

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Crystal structure

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Mineral properties

Formula: (Mn++,Fe++,Mg)(Al,Fe+++)₂O₄
Class: Oxides
Crystal system: Cubic
Typical colours: black, brown, red-brown
Lustre: Resinous, Vitreous
Hardness: 5.50-6.50
Specific gravity: 4.10-4.50
Crystal habit: Granular, Massive, Octahedral
Origin: manganese deposits, contact-metamorphic rocks and spinel-bearing metamorphic assemblages

What is Galaxite?

Galaxite is the manganese-rich spinel-group oxide, generally brown to black and found in manganese-rich metamorphic assemblages.

Mineralogy and structure

Reference formula: MnAl₂O₄. Galaxite forms a compositional series with other spinels. Natural material may contain iron and magnesium substitutions. Galaxite belongs to the oxides and has a cubic crystal system. Typical hardness is 5.5–6.5 on the Mohs scale and specific gravity is approximately 4.1–4.5.

Colour and appearance

Typical colours include brown, red-brown, black. The usual octahedral, granular, massive habit and vitreous, resinous lustre are useful descriptive features, but colour alone is not diagnostic.

Formation and localities

Galaxite forms in or is associated with manganese deposits, contact-metamorphic rocks and spinel-bearing metamorphic assemblages. Important documented localities include the United States, South Africa, Japan, Sweden, Brazil and Australia.

Collecting and care

Protect crystal edges and record the host rock because spinel-group compositions overlap.

Sources and editorial review

Reviewed by NotOnlyRocks Editorial Team

Last reviewed: 31 August 2026

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