sedimentary
River Siltstone / Mudstone Pebble
Siltstone (composed of mixed silicate and carbonate minerals)
Hardness: 3-5 (Mohs scale), Color: tan to light grey, Luster: dull/earthy, Crystal Structure: microcrystalline (not visible to naked eye), Cleavage: none, Specific Gravity: approx 2.5-2.7
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Physical properties
Hardness: 3-5 (Mohs scale), Color: tan to light grey, Luster: dull/earthy, Crystal Structure: microcrystalline (not visible to naked eye), Cleavage: none, Specific Gravity: approx 2.5-2.7
Formation & geological history
Formed through the lithification of fine-grained silt and clay particles deposited in low-energy aquatic environments. This specimen has been rounded by fluvial mechanical weathering (river transport) over thousands of years.
Uses & applications
Common industrial uses include fill material in construction, aggregate for road base, or raw material for cement; smooth pebbles can be used for landscaping and zen gardens.
Geological facts
Small rounded pebbles like this are often referred to as 'worry stones' because of their smooth texture. They represent the long journey a rock takes from its source outcrop down through a drainage basin.
Field identification & locations
Identify in the field by its smooth, ellipsoidal shape and fine-grained, non-crystalline surface. Common in riverbeds, glacial deposits, and beaches globally. It can be scratched by a steel blade but generally not by a fingernail.
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