sedimentary
Manganese-coated Sandstone
Clastic sedimentary rock with Manganese Oxide (often Pyrolusite or Psilomelane)
Hardness: 6-7 (sandstone parent), 2-6 (coating); Color: Tan/beige with black/dark brown patches; Luster: Dull to earthy; Crystal structure: Granular/clastic; Cleavage: None
- Hardness
- 6-7 (sandstone parent), 2-6 (coating)
- Color
- Tan/beige with black/dark brown patches
- Luster
- Dull to earthy
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Physical properties
Hardness: 6-7 (sandstone parent), 2-6 (coating); Color: Tan/beige with black/dark brown patches; Luster: Dull to earthy; Crystal structure: Granular/clastic; Cleavage: None
Formation & geological history
Formed through the accumulation and cementation of sand-sized mineral grains, primarily quartz. The black surface patches are formed by Manganese oxides precipitating from groundwater or surface water onto the rock surface (Mn oxide dendritic or film staining).
Uses & applications
Common sandstone is used in masonry, construction, and landscaping. Manganese-rich rocks can be ores for steel production, though this specific specimen is more of a common geological find for hobbyists.
Geological facts
Manganese dendrites are often mistaken for plant fossils because they form branching patterns that look like moss or ferns, but they are entirely inorganic mineral growths.
Field identification & locations
Identify in the field by its grainy, 'sandpaper' texture and the presence of non-organic black staining. Common in arid environments or riverbeds where mineral-rich water evaporates.
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