sedimentary
Sandstone with Manganese Dendrites
Arenite (mostly SiO2) with Manganese Oxide inclusions (MnO2)
Hardness: 6-7 (quartz grains); Color: Tan/orange background with black/dark brown spots; Luster: Dull/Earthy; Structure: Clastic; Cleavage: None
- Hardness
- 6-7 (quartz grains)
- Color
- Tan/orange background with black/dark brown spots
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 (quartz grains); Color: Tan/orange background with black/dark brown spots; Luster: Dull/Earthy; Structure: Clastic; Cleavage: None
Formation & geological history
Formed by the accumulation and cementation of sand-sized mineral grains, typically quartz. Black spots are dendritic manganese mineral growths precipitated from groundwater.
Uses & applications
Commonly used as a decorative stone, garden landscaping, building material, and for geological study.
Geological facts
The black spots are often mistaken for fossils but are actually mineral growths. The rounded shape suggests it was weathered by water in a river or coastal environment.
Field identification & locations
Identify by the sandpaper-like feel and the distinct branching or spotting manganese patterns. Found in desert and riverbed environments worldwide.
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