Beads:

Solid or boulder Opal cut and polished into spheres

Body Colour:

Degree of darkness of solid or boulder Opals (eg Light, Dark, Black)

Black Opal:

Solid opal with black body colour

Boulder Opal:

Presented in one piece where the Opal is naturally attached to the host rock in which it was formed

Boulder Splits:

Mirror image pairs of Boulder Opals often found when an Opal bearing boulder is opened (split) along a vein of Opal

Broad Flash:

Pattern displaying large single or multiple flashes of colour

Cabochon:

Relative height of the domed top of a stone

Calibrated:

Refers to industry standard sizes and shapes (eg 10x8 mm Oval)

Carats (cts):

International measure of weight for most gemstones including cut and polished Opals (1gm = approximately 5 cts)

Chinese Writing:

Pattern displaying flashes of colour in appearance similar to Chinese characters

Chip Opal:

Composition of small flat or irregularly shaped pieces of natural Opal encompassed in resin

Colour Bar:

Layer of colour in Opal differing from the layers above and below

Colour Intensity:

Relative brightness of the play of colour

Colours:

Predominant spectral colours (as per R,O,Y,G,B,I,V)

Common Opal:

Opal that does not display a play-of-colour

Crystal Opal:

Transparent to semi transparent solid Opal

Dark Opal:

Solid Opal with dark body colour

Doublet Opal:

Composition of a slice of natural Opal cemented to a dark base material

Field Name:

Specific name given to a location within a designated Opal mining area

Fire:

Common reference to the play-of-colour in Opal (eg Red fire)

Flagstone:

Pattern displaying proportionally large irregular flashes of colour

Flaw:

Fracture (can be surface or internal)

Free-Form:

Any 2 or 3 dimension shape that is not regular in form

Grams (gms):

International measure of weight (1 gm = Approximately 5 carats)

Hardness:

Opal registers between 5.5 - 6.5 on Moh's Scale of Hardness (Similar to glass)

Harlequin:

Extremely rare checkerboard pattern displaying clearly defined flashes of colour (originated in the likeness of the clown Harlequin)

Inclusion:

Impurity (can be surface or internal)

Jelly Opal:

A very transparent form of Opal usually displaying weak and indistinct colours as if suspended in gelatine

Light Opal:

Solid Opal with light body colour

Matrix Opal:

Presented in one piece where the Opal is naturally diffused through the host rock in which it was formed

Metal:

Descriptive reference to metals incorporated in jewellery items

Mosaic Opal:

Composition of small flat pieces of natural Opal cemented as a mosaic tile on a dark base material

Multi-Fire:

Opal displaying most colours with no particular colour predominating

Nobby:

Rough Opal formed as an unattached piece (Common to Lightning Ridge)

Opal:

Gemstone of hydrated amorphous silica with the chemical formula SiO2.nH2O

Origin:

Opal mining area in Australia where the Opal was likely to have been mined

Ounces Troy:

International measure of weight adopted for uncut rough Opal and specimens

Painted Lady:

Boulder Opal specimens from Andamooka in South Australia

Pattern:

Descriptive reference to size and type of play-of-colour

Pineapple:

Rare cluster of opalized crystals believed to be pseudomorph of ikiate crystals

Pinfire:

Pattern displaying a uniform array of very small colour flashes

Play-of-Colour:

Visible display of colours produced by diffraction of white light through a micro-structure of orderly arrayed silica spheres

Potch:

Opal that does not display a play-of-color

Precious Opal:

Opal that exhibits a play-of-colour produced by diffraction of white light through a micro-structure of orderly arrayed silica spheres

Quality:

Relative value range for the size and type of item (ie high, medium, low)

Ribbon:

Distinctive pattern where the colour rolls in parallel bands over the stone

Rolling Flash:

Pattern where single or multiple broad flashes of colour appear to roll as the stone is moved

Rough Opal:

Opal in its natural state as mined (apart from cleaning)

Semi-Black Opal:

Refers to Dark Opal

Shape:

Description of the 2 or 3 dimension form of a piece of Opal

Size:

Relative size for the type of item (ie small, medium, large)

Solid Opal:

Opal presented in one piece in its natural state apart from cutting and polishing

Straw Pattern:

Pattern displaying effect of sticks of colour randomly crossing each other

Total Weight:

Combined weight of complete item or group of items

Transparency:

Degree of translucence displayed (from transparent to opaque)

Treated Matrix:

Matrix Opal that has been treated to darken the body colour

Triplet Opal:

Composition of a slice of natural Opal cemented to a dark base material and a transparent top layer (usually of quartz or glass)

Webbing:

Visible web-like inclusion in some Opal (light or dark in colour)

Weight:

Weight of item expressed in carats, grams or ounces (troy) as appropriate (1 gram = approximately 5 carats) (1 ounce (troy) = approximately 31 grams)

Yowah Nut:

Small ironstone boulder with a kernel of Opal (from Yowah in Queensland)