Hag Stone (Piddock bored rock)

Physical Properties

Hardness: 3-4 (if limestone); Color: Tan, grey, beige; Luster: Dull or earthy; Structure: Highly porous with cylindrical or teardrop-shaped holes; Cleavage: None.

Formation & Geological History

Formed through bioerosion where boring mollusks, such as Piddocks, drill into softer sedimentary rocks (limestone, sandstone, shale) on the seabed over many years. These specimens are typically from the Holocene epoch.

Uses & Applications

Used primarily in home decor, as garden ornaments, or as metaphysical charms or amulets. In some cultures, they are used as 'luck stones'.

Geological Facts

Also known as Odin stones or witch stones, folktales suggest looking through the hole allows one to see into the fairy realm or ward off evil spells. The holes are actually the former homes of rock-boring clams.

Field Identification & Locations

Identify by the presence of smooth, circular, or tear-shaped through-holes that are not caused by simple water erosion. Commonly found on coastlines with soft sedimentary outcroppings, such as the UK and California coast.

Identified on: 5/15/2026

Mode: Standard