fossil

Orthoceras Fossil Limestone Egg

Fossiliferous limestone containing Orthoceras (Nautiloidea) and Goniatite remains (CaCO3)

AI-generated identification · may be incorrect

Hardness: 3 on Mohs scale (calcite/limestone matrix); Color: Black, charcoal grey, and white to light tan; Luster: Vitreous to sub-vitreous when polished; Cleavage: Rhombohedral (in calcite fills); Specific Gravity: ~2.6-2.8 g/cm³

Hardness: 3 on Mohs scale (calcite/limestone matrix)
Color: Black, charcoal grey, and white to light tan
Luster: Vitreous to sub-vitreous when polished

Identified October 3, 2026More fossil →

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Physical properties

Formation & geological history

Formed in warm, shallow marine environments during the Silurian to Devonian periods (approximately 390-440 million years ago). Deceased marine mollusks settled to the seabed and were encased in dark, carbonaceous lime mud, later recrystallizing into calcite-rich fossils within dense black limestone.

Uses & applications

Commonly carved and polished into decorative shapes such as eggs, spheres, plates, and bookends; popular among mineral and fossil collectors; used in educational displays and lapidary art.

Geological facts

Orthoceras was an ancient marine mollusk and ancestor of the modern squid and nautilus, featuring a straight, chambered internal shell divided by septa, connected by a central tube called a siphuncle visible in cross-sections.

Field identification & locations

Most commonly quarried in the Atlas Mountains near Erfoud, Morocco. Field identification is easily done by spotting the distinct conical, segmented white calcite chambers embedded in a dark limestone matrix that reacts effervescently with dilute hydrochloric acid.