Andesine

Andesine from the Portland Harbour Trust Quarry, Cape Grant, Portland, Victoria, Australia, measuring 58 × 38 × 28 mm and weighing 29 grams.

Andesine is a calcium-rich member of the plagioclase feldspar series; the International Mineralogical Association now treats it as a compositional variety within that series rather than a separate species, but the name remains in wide use among collectors and dealers. The quarry at Cape Grant exposes an eroded remnant of one of the volcanic vents along this stretch of Victoria's coast, and is a documented source of Andesine alongside Analcime, Augite and Ilmenite, the black crystals that Andesine from this locality is often found intergrown with.

This piece comes from the Allan Waldon Collection. Cape Grant feldspar doesn't come up for sale often, so it's a nice opportunity for anyone wanting a representative Victorian coastal volcanic locality alongside the better-known inland basalt quarries.