- Any of various small marine clams of the genus <em>Donax</em> having variously colored, often striped or banded wedge-shaped shells, and found especially on sandy beaches along the Atlantic coast of the United States.
- A soft porous limestone, composed essentially of fragments of shells and coral, used as a building material.
- A rock made up of fragments of marine shells, slightly consolidated by pressure and infiltrated calcareous matter.
- A soft, whitish, coral-like stone, formed of broken shells and corals, found in the southern United States, and used for roadbeds and for building material, as in the fort at St. Augustine, Florida.
- Any of several small <xref>marine</xref> <xref>clams</xref>, of the species Donax variabilis, common in <xref>US</xref> <xref>coastal</xref> <xref>waters</xref>.
- A soft form of <xref>limestone</xref> made of fragments of <xref>shells</xref>