Opal is hydrated silica and the refraction of light by silica spheres creates a play of colour when viewed from different angles. Do not confuse opal with "opalite" - this is a man-made synthetic stone, usually glass. For your convenience we sell our opals in matched pairs (matching opals is notoriously hard due to the play of colour displayed in these gems). With regard to colour, please pay attention to the description of the gems as photographing opals is extremely difficult. Hardness 6 (Mohs).