Beryl (var. emerald) in schist, Poona, WACollection Highlights | Updated 1 month ago Crystals of beryl (var. emerald) in schist from Poona, WA. Specimen is 8 cm long. WA Museum specimen number MDC1822 Geoff Deacon, WA Museum These crystals of dark green emerald in mica schist are from Poona near Cue. Emerald is a variety of beryl which contains small amounts chromium producing a dark green colour in the crystals. The beryllium-rich emerald formed in ultramafic rocks, the source of chromium, at the margin of a pegmatite, the source of beryllium. Gem Collection