sedimentary
Fossiliferous Siltstone
Clastic Sedimentary Rock with Fossil Inclusions
Hardness: 3-5 (Mohs), Color: Red-brown to rusty due to iron oxidation (hematite/limonite), Luster: Dull/Earthy, Structure: Fine-grained clastic matrix with visible bioclasts (shell fragments).
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Physical properties
Hardness: 3-5 (Mohs), Color: Red-brown to rusty due to iron oxidation (hematite/limonite), Luster: Dull/Earthy, Structure: Fine-grained clastic matrix with visible bioclasts (shell fragments).
Formation & geological history
Formed in low-energy marine or lacustrine environments where fine silts and mud settled over and preserved organic remains, later compacted and cemented over millions of years (likely Paleozoic to Mesozoic era).
Uses & applications
Primarily used for geological study, education, and as a collector's specimen. Fine-grained siltstones are sometimes used as low-quality building stone or fill material.
Geological facts
The reddish color suggests the rock was exposed to oxygen during or after formation, causing iron-rich minerals to oxidize. The curved white shapes are cross-sections of ancient brachiopod or bivalve shells.
Field identification & locations
Identify by its gritty feel (finer than sandstone but coarser than shale) and visible shell impressions. Common in sedimentary basins worldwide. Check for 'fizz' with weak acid to see if fossils are calcified.
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