The Virgin Rainbow opal on a turntable, showing the play of light on its surface. This opal has been described as \the finest ever\ due to its intense and contrasting colours. The Virgin Rainbow is some 66x14 millimetres in size, weighs more than 72 carats (14 grams), and is said to be worth more than a million Australian dollars. Opal is a mineraloid form of silica, in which the silica molecules form small spheres. These are packed in a semi-regular lattice with many local deformities. The spheres reflect and diffract light, and interference causes the wide variety of colours seen. This opal formed inside the fossilised rostrum of a belemnite, an extinct squid-like cephalopod. This opal was found in Coober Pedy, South Australia, in 2003. It was filmed at the South Australian Museum, Adelaide, in 2014. In 2015 it formed a major part of the \Opals\ exhibition, celebrating 100 years of opal mining at Coober Pedy.