GLOSSARY OF OPAL TERMS

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Agitator - or 'agi' for short; a modified cement mixer used to wash and tumble opal dirt. Usually set�up adjacent to a dam for water supply.

Amorphous - a word meaning "without form", applied to gems and minerals that have no definite or orderly arrangement of atoms or crystal structure and have no external crystal structure.

Andamooka - Mining Area in South Australia. Producing Crystal Opal and treating matrix opal

Artesian Basin - a large body of underground water that covers some 1,750,000 square kilometres or around 676,250 square miles in the inland of Australia and occurs in many other places in the world. A huge source of water by way of bores or wells in the arid areas.

Assembled Opal - Opal that has been glued together

Automatic hoist - a machine which can be activated from underground to pull a bucket up the mine shaft and tip its content out; used to carry opal dirt up and dump it into a truck.�

Ballroom - a term used to describe a large cavity in an opal mine where the opal dirt has been removed in the search for opal. These ballrooms can be quite large.

Bar - a descriptive term for the way the actual opal colour forms in a nobby or piece of seam opal, usually referred to as "the colour bar".

Beads - Solid or boulder Opal cut and polished into spheres

Black Crystal Opal - Solid opal which is transparent to translucent opal. Viewed from the top, it compares at least with N3 in darkness rating

Black opal � Any solid opal with an N rating between 1 to 4, it the most rare and valuable type of opal. Black opal has a dark body tone, which gives greater intensity to the gem colour. The word 'black' doesn't refer to the colours displayed by the opal - black opal comes in every colour of the rainbow, and is found in Lightning Ridge.

Blue Opal - Solid opal with a blue base color�

Blow - a formation resembling a cylindrical 'tube' varying in diameter from a few inches to many feet and found in the actual opal 'level', sometimes containing some opal fragments and made up of a whitish sandy material which is often very hard. Thought to be steam or pressure vents millions of years ago.

Blower - a machine like a giant vacuum cleaner, used to suck opal dirt from underground into a pipe, up the shaft and into a waiting truck. A more recent invention than the automatic hoist.� A blower can remove massive quantities of opal dirt.

Body Colour - Degree of darkness of solid or boulder Opals (eg Light, Semi-Black, Black) see N rating

Bogger - a small vehicle with a tipping scoop on the front, used in some mines to move opal dirt from the mine face to the mine shaft for transport up to the truck.

Boulder opal - mined in Queensland, this gem forms naturally on a dark brown ironstone.

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

Brilliance - Relative brightness of the play of colour measured on a scale of 1 to 5

Broad Flash - Pattern displaying large single or multiple flashes of colour

Bummy - a slang term used on the opal fields to describe a stone which has been cut with large or excessive backs on them.

Buyer - someone who buys opal from miners, runners, or other buyers.

Cabochon - the domed or convex top which is shaped and polished on a finished gemstone. i.e. a non-faceted surface which is rounded and smooth all over.

Calibrate - to cut a stone to an industry standard size, usually by template and the use of vernier calipers.

Carat - a unit of weight used to measure opals and other gemstones. One carat equals one fifth of a gram.

China Hat - a formation of rough opal nobby with a peaked centre, thought to be an ancient lily centre which has fossilised into opal. �

Chinese writing - Type of opal pattern with criss crossed strokes of colour looking like oriental letters

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

Clarity -The degree of transparency of an opal

Clarity Cross - A black cross on a white background to measure the degree of clarity of an opal

Cleave or Cleavage - the ability of a gemstone or mineral to break in a certain direction usually because of its crystal structure. In opal, the cleavage plane is totally irregular and somewhat haphazard. The veins of opal in boulder opal are sometimes cleaved apart to expose the opal.

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

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

Common Opal - This term describes all opal that doesn't have a play of colour, but rather is one or other of the base colours, e.g. white, grey, and black - i.e. potch.

Coocoran - A fairly large basin that, during flood times, becomes a lake some 7 kilometres long and 3 kilometres wide. More importantly it is the name for the largest opal field of late in the Lightning Ridge area. Used to describe the large group of opal mining fields around and beyond the lake. Nobbies are also found in the Coocoan

Cracked Opal - Opal with one or more breaks in the opal

Crazed Opal - Opal with a multitude of little cracks

Crystal opal - any kind of opal that is transparent or translucent.

Digger - a hydraulic machine with a digging claw, used underground to mine opal. The miner stands at the controls of the digger while it is operating.�

Directionality - Degree of which an opal's colorplay is showing when viewed from various angles

Dome - The arch of the top of an opal. Rated as high, medium and flat dome

Doublet - a doublet is made by fusing a dark backing (often natural black potch) to the back of gem opal, producing a double-layered gem with an appearance similar to black opal.

Dopping - the technique of adhering a stone to a stick in order to handle it better during the cutting and finishing processes, using a specially designed wax.

Drill - these days many miners buy or hire a large drill to explore prospective opal-bearing ground. The drill is used to bore holes up to nine inches diameter, bringing earth and rock to the surface to be inspected for indications of opal.

Drive - the name used to describe a tunnel dug for the extrication of 'opal dirt', usually situated directly below the roof to a depth of about six feet.

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)

Fire opal - a general term used to describe a bright or brilliant flash of colour within a stone. This is not a term which is generally used in Australia to describe opal. Often also used to describe opal with 'fire colours' (red-orange-yellow).

Flagstone - �Pattern displaying proportionally large irregular flashes of colour

Flaw - Fracture (can be surface or internal)

Fossils - a fossil is a remnant of what was, either whole or in part, but usually replaced by some other element, for example opal.

Free-form - A naturally shaped opal - something other than an oval or round shape

Gouge - a term used by miners to describe the action of gently picking at the face to find opal as opposed to actual digging. Gouging is done when checking for trace or when opal has been seen, so as to get it out quickly rather than waiting for the processing to be done.

Grams (gms) - International measure of weight (1 gm = 5 carats)

Grawin - A large opal field about 40km west of Lightning Ridge known as the home of the "Black Seam Opal" Nobbies are not found at Garwin. Because of the lack of available water opal is not "tailed out" or washed like the Lightning Ridge or Coocoran fields. It is sorted dry.

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

Harlequin - A regular mosaic-like chromatic pattern in rounded, angular, or roughly square patches of equal size

Hoist - A mechanical device pioneered in Lightning Ridge that takes the dirt from the mine to the surface automatically.

Inclusion - Any material that has formed internally in opal, such as matrix, sand or even mud, and occasionally Gypsum, also known as dendrite.

Ironstone - Rock that has a rusty reddish brown appearance and is composed of iron oxide, mostly a conglomerate. In boulder opal the actual opal is in or around this material, and is cut leaving the boulder host rock on the back of the stone.

Jelly Opal - A type of transparent crystal opal usually without colour but sometimes with indistinct, fuzzy colours

Level - The name given to that strata where opal could be potentially found - commonly called opal dirt.

Light Opal - Solid Opal with an N rating of 7 to 9 with light to white body colour. see White opal

Lightning Ridge - Mining town in New South Wales. Famous for its black opal

Matrix (1) � In Boulder opal it means "faced� iron stone with specks or little seams of opal running through it

Matrix (2) � In Lightning Ridge it means any opal which has inclusions of potch showing in and through the opal

Mohs' Scale - The internationally recognised scale for measuring hardness in gems and minerals.

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

Mullock or Mullock Heap - A term used to describe the piles of opal dirt lying on the surface on all the fields.

Multicolor Opal - Opal which has at least three distinct fire colors

Multi-Fire - Opal displaying most colours with no particular colour predominating. see Multicolour

Night Stone - Opal which shows very bright colors in low light

Nobby - a naturally lump-shaped piece of opal. The nobby form of opal is only found at Lightning Ridge and some of the surounding fields.�

N Rating � A scale between 1 to 9 used to measure the base tone of an opal. ��

Opal - An amorphous non-crystalline gem mineral solidified from gelatinous or liquid silica deposited in cracks and cavities left by decaying vegetation, wood, crustaceans and bones millions of years before. Very valuable in its 'black' forms and containing a reasonable content of water. Chemical symbol: SiO2 plus H2 O. In higher grades of opal the water content can be as high as 10%. Refractive Index of 1.38 - 1.60 and a hardness of between 5.5 to 6.5 on Mohs' scale.

Opal carving - a specialised method of opal cutting, used to conserve gem opal and to produce uniquely-shaped gemstones with freeform shapes and undulating surfaces.

Opal cutter - a skilled person who cuts rough or rubbed opal into cut and polished gemstones.

Opal dirt - claystones in which opal is found.

Opalised or Opalized fossil - opal which has filled a void in the earth caused by decomposed objects, in the shape of teeth, bones, shells, plants, etc.

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

Orientation - a term associated with opal cutting used to describe the skill of making the absolute best out of a rough piece of opal in terms of colour, shape pattern, etc. The art of getting the best out of a stone.

Ounces Troy - International measure of weight adopted for uncut rough Opal and specimens

Parcel - A collection of any number of opals, either rough, rubs or cut, offered for sale

Picture Stone - Opal which shows an images. This might be created by the precious opal or in combination with colors of the motherstone

Pinfire - Type of opal pattern where specks of different colours cover the whole stone

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

Potch - common or colourless opal - a form of non-precious opal that doesn't contain gem colour.�This can represent up to�90% of the weight of a cut opal.

Porcelenite - A fine clay or sand that is the opal dirt in which black opal is formed. Small amounts sometimes can be matrixed in with�the cut opal, usualy on the back.

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

Prop - an upright log used to support the roof of an underground mine.�

Puddler - Forerunner of the agitator, a mesh drum.

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

Ratter - a person despised on the opal fields. A thief who steals opal from a mine, an agitator or a pile of tailings.

Ribbon Pattern - Type of opal pattern with the colour running

Rolling Flash - Pattern where single or multiple broad flashes of colour appear to roll as the stone is moved in stripes

Rough Opal - opal that hasn't yet been touched by cutting equipment.

Rub - opal that has been roughly ground down or 'rubbed' by cutting machinery to remove gross impurities and establish a preliminary shape.

Runner - someone who sells opal to buyers on behalf of the owners of the opal, usually on a commission basis.

Saw - In terms of opal cutting, an automated diamond saw, comprising a circular blade with the outside edge coated with diamond. Used with water for lubrication and to avoid overheating of the opal.

Seam - a horizontal layer of opal in the ground. Opal is often found by miners by following a 'seam'. Very thin seam is known as 'trace'.

Seam Opal - Opal found in a layer rather than in nobbies

Semi-Black Opal - Solid Opal with an N rating between 5 and 6 showing a dark body colour

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

Solid Opal - A naturally occurring solid piece of opal, usually cut into a cabochon.

Straw Pattern - Pattern displaying effect of sticks of colour randomly crossing each other

Sunflash - Opal showing colour only from certain angles when exposed in light

Synthetic Opal - Opal grown in a laboratory. Present day manufacturers of synthetic opals include Pierre Gilson (the original manufacturer), Inamori (a Japanese manufacturer) and unspecified Russian and Chinese manufacturers

Tailings - Material left after opal dirt from the mine has been washed.

Transparency - �Degree of translucence displayed (from transparent to opaque)

Treated Matrix - Matrix Opal that has been treated to darken the body colour

Triplet - A three-part manufactured opal, comprising base material (usually black potch), opal (sliced very thin and glued to the black backing) and a quartz or optical glass top, giving the illusion of being a solid stone.

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 = 5 carats) (1 ounce (troy) = approximately 31 grams)

White opal - opal with a white or light body tone N7 to N9 on the base tone scale, normally found in South Australia.

Windlass - a winch used to haul opal dirt up out of the mine. These days, most miners use an automatic hoist or blower for this purpose.

Yowah Nut - Small ironstone boulder, containing opal either as a solid kernel or in concentric layers