sedimentary

Banded Siltstone or Mudstone

Clastic Sedimentary Rock (Siltstone/Argillite)

AI-generated identification · may be incorrect

Hardness: 3-5 on Mohs scale. Color: Greenish-grey and reddish-brown bands. Luster: Dull/Earthy. Texture: Fine-grained, smooth to the touch, clastic. Structure: Distinct parallel bedding or laminations.

Hardness: 3-5 on Mohs scale
Color: Greenish-grey and reddish-brown bands
Luster: Dull/Earthy

Identified July 18, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the deposition and lithification of fine-grained clay and silt particles in low-energy environments like lake beds or deep ocean basins. The colors result from oxidation states of iron (red for ferric, green for ferrous).

Uses & applications

Primarily used as decorative stones, in lapidary work for cabochons or tumbled stones, and sometimes in landscaping. Historically used for making simple tools or ornaments.

Geological facts

The distinct banding is known as rhythmite, which can represent seasonal changes in sediment deposition. This specific color contrast is often seen in Precambrian or Paleozoic formations.

Field identification & locations

Can be identified by the fine-grained texture that lacks the visible grains of sandstone and the rhythmic color banding. Commonly found in riverbeds and glacial deposits where they have been water-worn into smooth pebbles.