Spessartine

Spessartine from the North Mine, Broken Hill, N.S.W., Australia, measuring 54 × 40 × 33 mm and weighing 123 grams. A solid example of the manganese garnet that makes Broken Hill's host rock so distinctive to geologists and collectors alike.

Spessartine is the manganese-aluminium member of the garnet group, Mn3Al2(SiO4)3, and at Broken Hill it is not a late, open-space mineral like the Calcite elsewhere in this sale but an essential part of the banded "garnet rock" that hosts the main orebody, formed when the original manganese-rich sediments were subjected to the intense regional metamorphism that reshaped the whole deposit. That garnet-quartz banding is one of the signatures geologists use to trace the Broken Hill lode through the mine workings, and dark red-brown Spessartine crystals within it are a familiar sight to anyone who has studied the deposit's geology.

Garnet specimens of good crystal form are harder to come by from Broken Hill than the more celebrated secondary lead and zinc minerals, since Spessartine here tells the story of the rock itself rather than later mineralising fluids. This piece carries a double provenance, the David Vince Collection and the Ruth Coulsell Collection.