The Millstream deposit is located 2 kilometres west of Mount Finlayson on the west side of Millstream Road, 13 kilometres west-northwest of Victoria.

A lens of fine-grained, banded, partly recrystallized limestone, 100 metres long and 300 metre wide, is hosted within greenstone of the Wark Gneiss. The Wark Gneiss is possibly the metamorphic equivalent of a mafic unit of the Paleozoic Sicker Group, the latest metamorphism having taken place in the Jurassic. The banding dips from 40 degrees northwest to 20 degrees southeast. Irregular lenses and masses of white weathering wollastonite are reported to occur in the limestone.

A chip sample taken at 1.5-metre intervals across 15 metres in the northern quarry, contained 52.1 per cent CaO, 3.08 per cent MgO, 0.5 per cent insolubles, 0.04 per cent R2O3, 0.200 per cent Fe2O3, 0.004 per cent MnO, 0.013 per cent P2O5, 0.025 per cent sulphur, 43.8 per cent ignition loss and 0.14 per cent water (Bulletin 40, page 90).

Limestone was produced from two quarries 320 metres apart, prior to 1908 but no figures are available.