fossil
Bivalve Fossil (Clam Stone)
Phylum Mollusca, Class Bivalvia
Hardness: 3-4 (if limestone) to 7 (if silicified); Color: Grey, tan, or brown; Luster: Dull/earthy; Internal mold showing symmetrical valves; Specific gravity: 2.6-2.8
- Hardness
- 3-4 (if limestone) to 7 (if silicified)
- Color
- Grey, tan, or brown
- Luster
- Dull/earthy
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Physical properties
Hardness: 3-4 (if limestone) to 7 (if silicified); Color: Grey, tan, or brown; Luster: Dull/earthy; Internal mold showing symmetrical valves; Specific gravity: 2.6-2.8
Formation & geological history
Formed through the lithification of marine sediments. The organic shell dissolves over time, leaving a sediment-filled mold or a mineral-replaced cast. Most common in Paleozoic to Cenozoic marine strata.
Uses & applications
Scientific study, educational collections, and decorative garden/landscape stones.
Geological facts
Bivalves have existed for over 500 million years. This specific shape is an 'internal mold' or 'steinkern,' which is the rock that hardened inside the shell before the shell itself dissolved.
Field identification & locations
Found in sedimentary outcrops, riverbeds, and coastal regions globally. Identification is based on the heart or nut-like shape with a visible hinge line (commissure) where the two valves met.
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