The Red Mountain occurrence consists of a 12 to 28 metre thick by a 365 metre long zone of coarsely crystalline magnesite near the top of the Proterozoic Mount Nelson Formation.

The magnesite is massive pearl-white, coarsely crystalline with a buff colored weathered surface. It grades laterally into a grey, psuedo-fenestral dolomite and is underlain by a fine- grained dolomite with 1 to 5 centimetre thick chert lenses. Magnesite occurs as one centimetre long crystals and appears to replace dolomite near the basal contact. Locally the larger crystals within a matrix of 0.5 millimetre grains of magnesite give a distinct "porphyritic" (bimodal?) appearance. Considerable silica is present as scattered remnants of cherty patches.