Omars, are a distinctive type of glacial erratic that consists of dark siliceous greywacke and exhibits prominent rounded, often deep, hemispherical voids and pits.

The greywacke is identifiable by its low metamorphic grade and the 10–40% rock fragments, distinctive volcanic clasts, and spherical carbonate concretions that it contains.

Their rounded shape, whether found in glacial tills or glacial-fluvial (outwash) gravels, indicate that they were eroded from pre-existing littoral or fluvial deposits.

Omars are typically found associated with granules and pebbles of oolitic jasper that were transported from the Belcher Islands in Hudson Bay, Canada.

[1][2][3] The name given these glacial erratics refer to their source, which is the Proterozoic Omarolluk Formation in the Belcher Islands in southeast Hudson Bay.