igneous
Polished indigo gabbro tower
Indigo gabbro, a coarse-grained mafic plutonic rock composed chiefly of plagioclase and pyroxene, commonly with dark amphibole/biotite minerals
AI-generated identification · may be incorrectTypically black, charcoal, gray, or bluish-purple with mottled patches; polished surfaces have a glassy to waxy luster. Hardness is about 6–7 Mohs, with no consistent cleavage as a rock and moderate-to-high density (~2.8–3.1 g/cm³).
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Physical properties
Typically black, charcoal, gray, or bluish-purple with mottled patches; polished surfaces have a glassy to waxy luster. Hardness is about 6–7 Mohs, with no consistent cleavage as a rock and moderate-to-high density (~2.8–3.1 g/cm³).
Formation & geological history
Forms when mafic magma cools slowly deep in the crust, producing interlocking crystals; most commercial material is Paleozoic to Precambrian in age, depending on the quarry. The pictured piece is cut and polished into a faceted obelisk.
Uses & applications
Used for decorative carvings, bookends, spheres, towers, countertops, and ornamental stone; it has limited jewelry use. Common retail value is mainly determined by polish, size, pattern, and workmanship.
Geological facts
“Indigo gabbro” is largely a trade name rather than a formally distinct mineral species; some material sold under it may be related larvikite or other dark igneous rock.
Field identification & locations
Identify it by its heavy weight, coarse mottled black-gray texture, and absence of glassy translucence or individual gemstone crystals; confirm with streak, density, and thin-section/mineral analysis. Common sources include Madagascar, India, Finland, and other mafic-rock quarries.
