metamorphic

Likely biotite-rich schist or gneiss

Mica schist (quartz–feldspar–biotite assemblage; exact identification requires examination)

AI-generated identification · may be incorrect

The specimen appears dark brown to greenish-black, coarse and foliated, with reflective, platy mica grains. Biotite has Mohs hardness 2.5–3 and perfect basal cleavage; the rock’s hardness varies with its other minerals.

Identified September 29, 2026More metamorphic →

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Physical properties

Formation & geological history

Likely formed when clay-rich or other sedimentary rock was subjected to heat and pressure, aligning mica into layers. Metamorphic age cannot be determined from the photograph.

Uses & applications

Primarily a collector specimen or decorative stone; schist and gneiss are also used locally as building and landscaping stone.

Geological facts

The glittery surface is consistent with mica flakes reflecting light. The image does not show enough detail to distinguish schist from gneiss or rule out other dark, mica-bearing metamorphic rocks.

Field identification & locations

Look for visible, aligned mica flakes and a tendency to split along foliation; a fresh surface and magnification would help confirm it. The reported Baja California location makes regional metamorphic rock plausible, but does not establish provenance.