Rock Identifier
Fossilized Brachiopod Shell / Mold (Phylum Brachiopoda (Fossilized organic matrix replaced by Silica/Calcite)) — fossil
fossil

Fossilized Brachiopod Shell / Mold

Phylum Brachiopoda (Fossilized organic matrix replaced by Silica/Calcite)

Hardness: 3-7 (depending on calcified or silicified preservation). Color: Tan, yellowish-brown, grayish, with visible curved hinge structures and interior mold texture. Luster: Dull, earthy to slightly vitreous. Structure: Bivalved symmetry with unequal-sized dorsal and ventral shells.

Hardness
3-7 (depending on calcified or silicified preservation)
Luster
Dull, earthy to slightly vitreous
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Physical properties

Hardness: 3-7 (depending on calcified or silicified preservation). Color: Tan, yellowish-brown, grayish, with visible curved hinge structures and interior mold texture. Luster: Dull, earthy to slightly vitreous. Structure: Bivalved symmetry with unequal-sized dorsal and ventral shells.

Formation & geological history

Formed in ancient shallow marine environments when dead marine organisms were buried in soft sediment. Over millions of years (often Ordovician to Carboniferous periods), minerals dissolved and recrystallized, creating a fossil cast or permineralized shell.

Uses & applications

Used primarily for educational display, paleontology research, and personal collections by rockhounds.

Geological facts

Brachiopods are marine invertebrates that look somewhat like modern clams, but they are not closely related. While clams have left and right shells that are mirror images, brachiopods have top and bottom shells that differ in shape.

Field identification & locations

Identify in the field by looking for distinctive curved shell hinges, ribbed patterns, or cavity impressions in limestone or chert matrices. Common in fossil-rich sedimentary exposures worldwide.

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