metamorphic

Weathered metamorphic rock, likely schist or phyllite

Quartz–mica schist/phyllite (exact identification requires a fresh surface and tests)

AI-generated identification · may be incorrect

Gray-brown, fine- to medium-grained, dull to weakly silky luster, with probable mica foliation and a prominent fracture. Typical hardness is about 2–7 depending on mica versus quartz content; specific gravity roughly 2.6–2.8. No obvious crystal faces are visible.

Identified September 14, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when shale or mudstone was buried and subjected to directed heat and pressure, producing aligned mica minerals and foliation. The specimen is probably Paleozoic–Mesozoic or younger; its exact age cannot be determined visually.

Uses & applications

Used locally as landscape stone, fill, and occasionally thin decorative slabs; attractive schist can be collected, but this piece has modest commercial value.

Geological facts

The planar fabric and silvery granular texture distinguish it from most unfoliated igneous rocks. The apparent split may be natural foliation or a later break.

Field identification & locations

The reported Sacramento-area location is plausible for weathered metamorphic cobbles transported from nearby Sierra Nevada or foothill terranes, though local gravel sources can mix many rock types. Check for flakes that separate, a silky sheen, and streaks of quartz; a fresh break and dilute acid test would improve identification.