sedimentary
Siltstone
Siltstone (primarily composed of quartz and clay minerals)
Hardness: 3-4 (Mohs); Color: Tan, beige, grey, or brown; Luster: Dull/Earthy; Texture: Fine-grained, gritty feel (finer than sandstone); Structure: Clastic, often shows layering or fissility.
- Hardness
- 3-4 (Mohs)
- Color
- Tan, beige, grey, or brown
- Luster
- Dull/Earthy
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Physical properties
Hardness: 3-4 (Mohs); Color: Tan, beige, grey, or brown; Luster: Dull/Earthy; Texture: Fine-grained, gritty feel (finer than sandstone); Structure: Clastic, often shows layering or fissility.
Formation & geological history
Formed from the lithification of silt-sized particles (0.0039 to 0.0625 mm) deposited in low-energy environments such as river floodplains, lakes, or marine basins. These sediments accumulate over millions of years and compact into rock.
Uses & applications
Mainly used as fill material in construction, for flagstones in landscaping, and occasionally as a source of clay for ceramics if the composition is right.
Geological facts
Siltstone is intermediate between sandstone and shale. While it looks like shale, it lacks the thin, splitting laminations (fissility) that define true shales.
Field identification & locations
Identify in the field by its gritty 'sandpaper' feel on the teeth (a common field test) and its fine-grained, non-glossy appearance. It is found globally in sedimentary basins.
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Sandstone or Siltstone
Arenite (if sandstone)
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Brown Sandstone (River Rock)
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Mudstone
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Cone-in-cone structure (Limestone)
Cone-in-cone structure (Secondary Sedimentary Structure)
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Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
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Sandstone
Arenite (primarily SiO2)
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