Gemstone Beach, Orepuki

The most prized stone on the beach is a mineral called hydrogrossular. It occurs as rare, hard, translucent, waxy-whitish green pebbles 1-10cm in size. Hydrogrossular is a calcium aluminum garnet with water in its mineral structure (most garnets have no water). As they are loose pebbles on a beach, it's clear that the hydrogrossulars have come from somewhere else. That somewhere is the Countess Range where the garnets form in rocks called rodingites in the Dun Mountain Ophiolite Belt. They have been tumbled and polished in a 150 km journey down the Eglinton and Waiau valleys.

The smooth and wet pebbles reveal a variety of rich colours and textures. There are many different kinds of rock.

(1) hydrogrossular (waxy whitish green)

(2) epidosite (apple or pistachio green)

(3) jasper chert (hard, deep red)

(4) rhyolite porphyry (pale red, scattered feldspar crystals)

(5) granite (grey, interlocking crystals)

(6) quartz (white, milky)

The sand on the beach is different again in composition. There are concentrated pockets of black sand and tracks and traces of reddish sand. The black sand grains are magnetite and the red ones almandine garnet. These, too have come from Fiordland.