Opal Crystals
Meaning of Opal
Pink Opal Physical Properties
Opal is a hardened silica gel, normally containing between 5 and 10% water. Therefore it is non-crystalline (amorphous) unlike most other minerals. There are two varieties, precious opal and common (potch) opal. Precious opal is milky white or black, with a interplay of colours red, blue and yellow. Precious opals show iridescence (flashes of colour) depending on the angle it is viewed. The iridescence is due to the way the regular structure of small silica spheres diffracts light (the larger the spheres the larger the range of colour seen). Common (Potch) opal displays no iridescence of colours and is often opaque, its colours include black, grey or green. Opal is transparent to opaque, with a vitreous, resinous, waxy or pearly lustre and its streak is white. Group OXIDES, Composition SiO2.nH2O, Hardness 5.5-6.5, Crystal structure AMORPHOUS