Sedimentary / Metamorphic

Brecciated Limestone or Marble Pebble

Breccia / Calcite (CaCO3)

Hardness: ~3 on the Mohs scale, Color: dark gray to black with lighter gray/white veins, Luster: dull to faintly waxy (smoothed by water), Crystal structure: massive/microcrystalline (calcite veins may show crystal cleavage), Cleavage: none visible on the whole rock, perfect rhombohedral in calcite veins but microscopi…

Identified May 31, 2026More sedimentary / metamorphic →

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Physical properties

Formation & geological history

Formed initially as limestone in a marine environment. Later tectonic forces fractured the rock (brecciation), and groundwater rich in calcium carbonate filled the fractures, crystallizing as lighter-colored calcite veins. The rounded shape indicates it was subsequently eroded, transported, and tumbled by water (river or beach action).

Uses & applications

Larger deposits are used for decorative stone, tiles, or construction gravel. A small tumbled pebble like this is mainly of interest for casual collection or landscaping.

Geological facts

The intricate web of veins is a classic sign of 'brecciation'—where a rock is broken apart and glued back together by mineral deposits. Often colloquially called 'Picasso stone' or similar trade names if patterned extensively.

Field identification & locations

Identify by its reaction to weak acid (it should effervesce/fizz due to the calcite). Often found in riverbeds, glacial moraines, or beaches where limestone is a common bedrock.

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Anthracite Coal

Anthracite (Carbon-based organic sedimentary/metamorphic rock)

metamorphic

Coal (Anthracite)

Anthracite (Carbon-based organic sedimentary/metamorphic rock)

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Quartz Vein in Host Rock

Silicon Dioxide (SiO2) within Sedimentary/Metamorphic Matrix

Metamorphic or Igneous (context dependent)

Sandstone, Quartzite, and River Pebbles

Silicon Dioxide (SiO2) based Sedimentary/Metamorphic structures

Sedimentary and Metamorphic