Opal Patterns

I was reading more information about opals today and stumbled upon http://www.molsci.csiro.au on this website I found this informative piece about Opal patterns. They also have a few photo examples that you might want to check out.

Types & Patterns of Gem Opal

The descriptions below are taken, by kind permission, from Andrew Cody's book Australian Precious Opal (R1481). The reader should refer to that publication for an authoritative account of Australia's national gemstone: Block pattern: pattern displaying large particles of colour Broad flash: large areas of flash in the opal Chaff pattern: small blocks of colour giving an appearance of chaff Chinese writing: patches of colour forming hieroglyphs reminiscent of Chinese script Crystal: transparent or translucent opal where the colours are sharp and visible below the surface Fire opal: a term used for that opal where the base colour (as distinct from the diffraction colours) has a red or orange tone. This material generally comes from Mexico Flagstone: a pattern having definite patches of colour with the appearance of flagstone paving. Less regular than harlequin Flash: a pattern which consists of large flashing areas of colour Harlequin: very rare and most sought after opal, the colours form naturally in a chequerboard pattern. This is a collector's item footnote Jelly: transparent opal with 'jelly' appearance, colours generally hazy Milky: an opal with a creamy body colour which dominates the diffracted colour Multi-fire: a stone which has most colours without any particular colour dominating. Pinfire: a pattern of tiny dots of colour across the stone. Red on black: type of black opal which displays predominantly red. Extremely valuable. Ribbon pattern: colour bands across the stone. Rolling flash: unusual pattern displaying colours which 'roll' across the stone. Straw pattern: rare pattern; the colours in the opal look like straws.