Opal is probably the most famous phenomenal stone displaying the unparalleled play-of-colour, a rainbow-coloured kaleidoscopic effect. The name opal derives from the word 'opalus' given by the Romans, which is Latin for 'precious stone'. They can be fragile which makes it more suitable for jewellery such as necklaces, brooches and earrings that are less likely to be knocked. Opal is the birthstone for October. Mohs Scale of Hardness: 5.5 - 6.5 Sources: Australia, Ethiopia and Brazil. The finest quality and most durable opals generally come from Australia.;;Stone Size (mm): 12.8x8.0x2.5;Carat Weight (ct): 2.35