Rock Identifier
Fossil Sponge / Horn Coral / Crinoid Stem (Phylum Porifera or Cnidaria fossilized in calcium carbonate / silica) — fossil
fossil

Fossil Sponge / Horn Coral / Crinoid Stem

Phylum Porifera or Cnidaria fossilized in calcium carbonate / silica

Hardness: 3-4 (if calcite/limestone) or 7 (if silicified); Color: Tan to light brown with weathered white patina; Luster: Dull to earthy; Structure: Asymmetrical cylindrical, mushroom-like, or nodular shape formed by fossilization.

Hardness
3-4 (if calcite/limestone) or 7 (if silicified)
Color
Tan to light brown with weathered white patina
Luster
Dull to earthy
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Physical properties

Hardness: 3-4 (if calcite/limestone) or 7 (if silicified); Color: Tan to light brown with weathered white patina; Luster: Dull to earthy; Structure: Asymmetrical cylindrical, mushroom-like, or nodular shape formed by fossilization.

Formation & geological history

Formed during the Paleozoic or Mesozoic eras (e.g., Ordovician to Cretaceous) when marine organisms were buried in sediment and their hard parts were replaced by minerals like silica or calcite through permineralization.

Uses & applications

Collected by fossil enthusiasts, used for educational purposes and paleontology studies.

Geological facts

Fossils of this type are often found in ancient seabeds, recording marine biodiversity from hundreds of millions of years ago when shallow seas covered large parts of continents.

Field identification & locations

Look for distinctive branching, cup-like, or mushroom-like shapes that deviate from normal water-worn pebbles. Commonly found in limestone and sedimentary rock outcrops, stream beds, and gravel bars in regions with marine sedimentary history.

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