English: Maclurites magna LeSueur, 1818 - fossil gastropod in limestone ("Champlain Black Marble") from the Ordovician of Vermont, USA.

In the commercial decorative stone trade, “marble” is used to refer to a wide variety of relatively soft rocks (H = 3 to 5) that will take a fine polish. These include true marbles and rocks that aren’t marbles, such as limestones, tectonic breccias, and serpentinites. True limestones are calcitic biogenic and ~chemical sedimentary rocks.

The black material shown above is called "Champlain Black Marble", but is really Ordovician-aged limestone of the Crown Point Limestone. Decent-sized fossils are commonly encountered in this rock, such as gastropods, cephalopods, and bryozoan colonies.

The fossil seen here is a moderately large, low-spired gastropod called Maclurites magna. The gastropods (snails & slugs) are a group of molluscs that occupy marine, freshwater, and terrestrial environments. Most have a calcareous external shell (the snails). Some lack a shell completely, or have reduced internal shells (the slugs & sea slugs & pteropods). Most members of the Gastropoda are marine. Most marine snails are herbivores (algae grazers) or predators/carnivores.

Maclurites magna is sometimes jokingly called "Big Mac".

Classification: Animalia, Mollusca, Gastropoda, Archaeogastropoda, Euomphalina, Macluritoidea, Macluritidae

Stratigraphy: Crown Point Limestone, lower Middle Ordovician

Provenance: attributed to a quarry in Vermont, USA (possibly from the Fisk Quarry or the Goodsell Quarry)

Locality: floor paving stone in the Ohio Statehouse, downtown Columbus, Ohio, USA