Dolerite ventifact from Antarctica. (public display, Nebraska State Museum of Natural History, Lincoln, Nebraska, USA)

Ventifacts are lustrous, polished rocks with subplanar to curved facets. They form by natural abrasion and polish by winds that carry sand grains. Ventifacts are naturally sand-blasted rocks.

The rock itself is dolerite, also known as diabase. It is the shallow intrusive equivalent of basalt. Specimen-wise, it is essentially identical to basalt - a mafic, aphanitic igneous rock composed of plagioclase feldspar and pyroxene.

From museum signage: "Rocks exposed to very long periods of wind action and dust storms show "carved" shapes ("ventifacts") produced by wind erosion. Professor San Treves of the University of Nebraska at Lincoln collected this ventifact. Some basalt rocks photographed by the Mars rovers may be ventifacts."

Geologic unit: unrecorded/undisclosed, but almost certainly derived from the Ferrar Dolerite, Jurassic