Rock Identifier
Fossil Belemnite Guard (Belemnitella spp. (rostrum)) — fossil
fossil

Fossil Belemnite Guard

Belemnitella spp. (rostrum)

AI-generated identification · may be incorrect

Hardness: 3.5-4 on Mohs scale (calcite); Color: brownish, yellowish-tan, or grey; Luster: vitreous to dull; Crystal structure: hexagonal (calcite composition); Cleavage: perfect rhombohedral; Specific gravity: 2.71

Hardness
3
Color
brownish, yellowish-tan, or grey
Luster
vitreous to dull
Identified More fossil →
Explore Fossil Belemnite Guard in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App StoreGoogle Play

Physical properties

Hardness: 3.5-4 on Mohs scale (calcite); Color: brownish, yellowish-tan, or grey; Luster: vitreous to dull; Crystal structure: hexagonal (calcite composition); Cleavage: perfect rhombohedral; Specific gravity: 2.71

Formation & geological history

Formed during the Mesozoic era (Jurassic to Cretaceous periods, roughly 200 to 66 million years ago) when the internal calcite skeleton (rostrum) of an extinct squid-like cephalopod became fossilized through mineral replacement in marine sediment.

Uses & applications

Used by paleontologists as index fossils for dating marine sedimentary strata and highly prized by fossil collectors.

Geological facts

Belemnites are closely related to modern squids and cuttlefish. Their bullet-shaped guards were commonly known as 'thunderstones' in folklore, as people historically believed they fell from the sky during lightning storms.

Field identification & locations

Easily identified by its distinctive bullet, dart, or cigar shape, solid calcite composition, and often showing a fibrous radial structure or a tiny apical canal when broken or sectioned. Commonly found in chalk deposits and marine limestone formations.

More like this

Other fossil specimens

Probable fossil-bearing rock or mineral concretion (Unidentified carbonate-rich concretion with a possible fossil inclusion) — fossil

Probable fossil-bearing rock or mineral concretion

Unidentified carbonate-rich concretion with a possible fossil inclusion

fossil
Likely fossil oyster shell (Fossilized bivalve shell; exact species cannot be identified from the image) — fossil

Likely fossil oyster shell

Fossilized bivalve shell; exact species cannot be identified from the image

fossil
Crinoid Stem Fossil in Matrix (Phylum Echinodermata, Class Crinoidea) — fossil

Crinoid Stem Fossil in Matrix

Phylum Echinodermata, Class Crinoidea

fossil
Fossiliferous limestone (likely a crinoidal or shell-fragment limestone) (Bioclastic limestone, composed chiefly of calcite (CaCO₃)) — sedimentary

Fossiliferous limestone (likely a crinoidal or shell-fragment limestone)

Bioclastic limestone, composed chiefly of calcite (CaCO₃)

sedimentary
Porous limestone pebble (Calcite-rich limestone (primarily CaCO₃); exact identification is uncertain from the image) — sedimentary

Porous limestone pebble

Calcite-rich limestone (primarily CaCO₃); exact identification is uncertain from the image

sedimentary
Weathered fossil bone fragment (identification uncertain) (Fossilized bone; exact taxon and mineral composition cannot be determined from the image) — fossil

Weathered fossil bone fragment (identification uncertain)

Fossilized bone; exact taxon and mineral composition cannot be determined from the image

fossil