igneous

Black granite (likely polished gabbro or diabase)

Granitoid rock dominated by feldspar, quartz, and dark mafic minerals; exact identification requires testing

AI-generated identification · may be incorrect

Coarse-grained, dark gray to black with reflective interlocking crystals and polished luster; typical hardness about 6–7 Mohs, no strong cleavage as a rock, and specific gravity roughly 2.7–3.1.

Identified August 11, 2026More igneous →

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At a glance

Common name: Black granite (likely polished gabbro or diabase)
Scientific name: Granitoid rock dominated by feldspar, quartz, and dark mafic minerals; exact identification requires testing
Category: igneous
Identified: August 11, 2026
Method: Standard

AI Estimated Value

Approximately $10–$50 for a small polished specimen; about $40–$150 per square foot for commercial slabs, depending on rarity and finish.

Not an official valuation

AI estimate for general interest only — not an appraisal. Actual value depends on condition, provenance, and market demand. Verify with a professional before buying, selling, or insuring.

This identification was generated by AI and may contain errors. Verify important details before relying on them — and never use an AI result to judge whether a specimen is safe to handle. Read the full disclaimer

Physical properties

Coarse-grained, dark gray to black with reflective interlocking crystals and polished luster; typical hardness about 6–7 Mohs, no strong cleavage as a rock, and specific gravity roughly 2.7–3.1.

Formation & geological history

Slow cooling of silica-rich to mafic magma produced visible crystals, generally during Precambrian to Phanerozoic intrusive activity. The glossy surface indicates cutting and polishing.

Uses & applications

Widely used for countertops, flooring, monuments, tiles, and architectural stone; attractive slabs have moderate decorative value rather than gemstone value.

Geological facts

Commercially labeled “black granite” may technically be gabbro, norite, diabase, or anorthosite rather than true granite. The image shows reflective platy minerals, possibly biotite or amphibole, mixed with feldspar.

Field identification & locations

Identify by visible interlocking crystals, great durability, and lack of fizz in dilute acid; a streak, hardness, and thin-section test can separate gabbro from granite. Common sources include India, Brazil, Scandinavia, South Africa, and Zimbabwe.