Glossary Of Opal Terms

When it comes to talking about opals, there are some terms that might seem a bit strange. Ratters, Nobbys, and Tailings are all part of the vocabulary of Opal. In this guide, we will outline a list of the most common terms used in the Opal industry, including types of opals and opal mining terms.

• Agate Opal. Banded variety of opal resembling Agate.

• Amatite. Opal in the form of thick mounds, formed from hot silica-rich springs. See also Geyserite.

• Amber Opal. Opal with a brownish to yellowish background colour, resembling Amber.

• Andamooka Opal. Opal from Andamooka, South Australia.

• Banded Opal. Form of Common Opal with colour bands. Synonym of Agate Opal.

• Bandfire Opal. Precious Opal with play of colours in wavy bands.

• Belemnite Opal. Opalized fossil of ancient octopus-like sea creatures (cephalopods) called Belemnites. Famous example is the Virgin Rainbow Opal. 

• Black Opal Body Tone. N1 to N4.

• Black Opal. Precious Opal with a black, dark blue, dark green, dark grey, or similar darkly coloured background or base colour. Black Opal is the most valuable form of opal mined in Lightning Ridge.

• Bone Opal. Opal pseudomorph after a bone.

• Boulder Opal. Precious Opal from Queensland, Australia, found in the cracks of, or as coatings on, ironstone or sandstone boulders.

• Cachalong Opal. Opaque, highly porous type of Common Opal.

• Cherry Opal. Orange-red to bright red variety of Mexican Fire Opal.

• Chinese Writing Opals. Type of opal pattern with criss-crossed strokes of colour looking like oriental letters.

• Chloropal. Common Opal similar to Prase Opal, but with a lighter green hue.

• Chrysopal. Common Opal similar to Prase Opal, but with a golden-green colour.

• Claro Opal. Transparent Precious Opal from Mexico with an intense red, green, blue, and yellow play of colour.

• Common Opal. Any Opal lacking play of colour.

• Contra Luz Opal. Precious Opal where the play of colour is visible only when a light source is behind the stone. Contra luz translates to "behind the light." 

• Coober Pedy Opal. High quality Precious Opal from Coober Pedy, South Australia.

• Crystal Opal. Transparent to translucent Precious Opal where play of colour is visible on the surface and in the interior of the stone.

• Dark Opal. Synonym of Black Opal.

• Dendritic Opal. Common Opal with dark inclusions that form mossy or fern-like patterns. Also called "moss opal" or "mossy opal." 

• Diatomite. Opal replacement of microscopic shells of diatoms (type of microscopic organism) clustered together. It is white, opaque, and chalky in texture. Synonym of Tripolite, Fuller’s Earth, and Diatomaceous Opal.

• Ethiopian Opal. From Welo and Gondar, newly discovered opal fields in Ethiopia, direct from opal wholesalers and miners. Many are porous, hydrophane opals and Ethiopian precious opals have brilliant play of colour.

• Fire Opal. Fire Opal is incorrectly used to describe Precious Opal, or Opal with play of colour. The true definition of Fire Opal is Opal with an orange to red colour. If the Fire Opal displays play of colour, it is more correctly known as Precious Fire Opal.

• Flame Opal. Precious Opal where the play of colour consists of red streaks or bands that flicker like a flame when the stone is rotated.

• Flash Opal. Precious Opal with large schillers that abruptly appear and disappear as the stone is rotated.

• Flashfire Opal. Synonym of Flash Opal (see above)

• Fossil Opal. Opal pseudomorph of organic matter such as shell, bone, and trees.

• Freeform Opal. A naturally shaped opal - something other than an oval or round shape.

• Gelite. Opal (or Chalcedony) as an accessory mineral that acts as the bonding agent of Sandstone or other cemented rock fragments.

• Geyserite. Opal formed from the deposition of hot water springs. Also called Perlite, Fiorite, or Geyser Opal. See also Amatite.

• Gilson Opal. Synthetically produced Opal.

• Girasol. Yellow or orange variety of Precious Opal in which the play of colour seems to follow the sun as the stone is rotated.

• Glass Opal. Synonym of Hyalite

• Gold Opal. Common Opal with a golden hue.

• Gondor. Opal from Gondor, Ethiopia.

• Harlequin Opal. Precious Opal in which the play of colour is arranged in a consistent harlequin, diamond-shaped, or rectangular-shaped pattern that is very vivid. Harlequin Opal is one of the rarest and most prized forms of Opal.

• Honey Opal. Transparent to translucent Opal with an orange to orange-brown, honey-coloured background. It may or may not display play of colour.

• Hungarian Opal. Any Precious Opal from Europe. However, nowadays this term often refers to any White Opal, regardless of where it was found.

• Hyacinth Opal. Synonym of Girasol.

• Hyalite. Colourless, misty-blue, or sky-blue transparent variety of Common Opal. Usually forms botryoidal masses as well as strange and unusual forms. All Hyalite fluoresces green.

• Hydrophane. White, opaque, highly porous Opal, that, when placed in water, allows the water to seep into it. This causes the stone to become transparent and almost invisible while in the water.

• Iridot. Old name given to Opal for a short period of time when Opal had a reputation of causing bad luck.

• Isopyre. Impure, dark red form of Opal. Isopyre was once thought to be a separate mineral.

• Jasper Opal. Brecciated Jasper in which the cementing material is Opal.

• Jelly Opal. A transparent Precious Opal with a gelatinous appearance and a bluish sheen. Jelly Opal may also refer to a colourless, transparent Common Opal. Synonym of Water Opal.

• Lechosos Opal. Precious Opal with a milky-white background colour displaying a strong play of colour. May also refer to Opal with a strong green schiller.

• Lemon Opal. Common Opal with a lemon-yellow colour.

• Levin Opal. Precious Opal with long and thin, lightning-like flashes.

• Light Opal. Synonym of White Opal.

• Lightning Ridge Opal. Opal from Lightning Ridge, New South Wales, Australia. Although different forms of Opal are found there, this term usually represents the high-quality Black Opal found there.

• Lithoxyl Opal. Wood Opal where the original structure of the tree is very apparent.

• Liver Opal. Synonym of Menilite (see below)

• Menilite. Opaque, greyish-brown form of Common Opal. Also known as Liver Opal.

• Mexican Fire Opal. Form of transparent Opal from Mexico, usually with an orange or red colour, highly desired as a gem. Although scientifically considered a Common Opal, it is rather rare and much sought after. If it exhibits a play of colour, it is known as Precious Fire Opal.

• Milk Opal. Opal with a milky-white colour. Controversy exists whether the name Milky Opal is coined for a milky white Common Opal or a milky white Precious Opal.

• Monarch Opal. Technically called Sterling Opal. Newer man-made opal with very similar appearance to natural opal, including black potch lines or snake/honey-comb patterns. Other names include Galaxy Opal, Monet Opal, and Exodus Opal.

• Moss Opal. Common Opal containing inclusions resembling moss. Synonym of Dendritic Opal.

• Mother of Opal. Precious Opal with bright colour specks filling the pores of sandstone or ironstone.

• Mother of Pearl Opal. Banded Opal used as cameos.

• Mountain Opal. Opal from igneous environments. Also called Volcanic Opal.

• Neslite. Common Opal similar to Menilite, but darker grey in colour. It was once a popular material for sword handles.

• Nevada Opal. Opal from the Virgin Valley (Humboldt Co.), Nevada, USA. 

• Onyx Opal. Common Opal resembling banded Onyx.

• Opal Matrix. Thin layer of Precious Opal on host rock. Small rock fragments are used in jewellery.

• Opaline. Opaline is synonymous with Opal Matrix (above) but was also an old term used to describe Opal from Australia.

• Opalite. Opalite has many connotations. It may refer to an impure form of Opal Myrickite black glass, a yellow-green Common Opal with black inclusions, or an imitation Opal produced from resin.

• Opalized Bone. Synonym of Bone Opal

• Opalized Fossil. Synonym of Fossil Opal

• Opalized Shell. Synonym of Shell Opal

• Opalized Wood. Synonym of Wood Opal

• Painted Boulder. Sandstone boulders with a coating of Precious Opal. When used in jewellery, this term is synonymous with Opal Matrix.

• Parcel. A collection of any number of opals, either rough, rubs, or cut,  that are offered for sale.

• Pearl Opal. Synonym of Tabasheer

• Peruvian Opal. Relatively rare Common Opals from Peru only found in the Andes Mountains. Often synonymous with blue opals or pink opals, the most notable Peruvian varieties.

• Pineapple Opal. Opal pseudomorph after Ikaite that resembles a pineapple. It is found only in White Cliffs (New South Wales), Australia. The pseudomorphed mineral was originally thought to be Glauberite, but studies now prove it to be Ikaite.

• Pinfire Opal. Precious Opal with very small, pinhead-size colour flashes.

• Pinpoint Opal. Australian synonym of Pinfire Opal

• Pipe Opal. Opal formed as a filling of long, cylindrical cavities in rock. Pipe Opals range in size from several inches to many feet.

• Pitch Opal. Yellow to brown Common Opal with a pitchy lustre.

• Potch. Australian term for Common Opal.

• Prase Opal. Green to dark green form of Common Opal.

• Precious Fire Opal. Fire Opal displaying play of colour.

• Precious Opal. Any Opal exhibiting a play of colour.

• Prime d’Opal. Synonym of Mother of Opal

• Pyrophane. Precious Opal in which the play of colour wanders about and reappears at random. This term is sometimes incorrectly used to describe Girasol.

• Queensland Opal. Synonym of Boulder Opal

• Quinzite Opal. Rose to pink coloured Opal. It is usually without play of colour, but a few examples displaying play of colour are known. Quinzite Opal is synonymous with Quinzite, Quincite, Quincite Opal, and Rose Opal.

• Radiolite Opal. Common Opal of a smoky-brown colour caused by inclusions of the exoskeletons of a unicellular marine organism known as radiolaria. May also be called Radio Opal.

• Rainbow Opal. Precious Opal where the play of colour is seen in curved bands, somewhat resembling a rainbow.

• Red Flash Opal. Precious Opal with red colour flashes that swiftly appear and disappear as the stone is rotated.

• Resin Opal. Common Opal with a yellow-brown colour and resinous lustre.

• Ribbon. Type of opal pattern with the colour running in stripes.

• Rough. Opal in its natural state; as it comes out of the ground .

• Rumanite. Opal from Romania.

• Seam Opal. Opal found in the seams or large cracks of rock. May also specifically refer to masses of white Common Opal containing bands of precious White Opal.

• Semi Black Opal. Body tone below N4 grey based Lighting ridge opal.

• Semiopal. Term sometimes used to describe any type of Common Opal, but many times alludes to particular forms of Common Opal, such as Wax Opal, Prase Opal, etc. Semiopal is also written as Semi-opal, and is synonymous with Half-opal.

• Shell Opal. Opal pseudomorph after a shell.

• Slocum Stone. A synthetically grown Opal. Also called Slocum Opal.

• Sun Opal. Name that describes several types of Opal. May refer to Fire Opal, Mexican Fire Opal, Honey Opal, or Amber Opal.

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

• Tabasheer. Opal occurring as an organic by-product. It forms by the hardening of a secretion issued from certain bamboo, forming a porous, rounded mass of Opal.

• Virgin Valley Opal. Opal from the Virgin Valley (Humboldt Co.), Nevada.

• Wash Opal. Waterworn Opal pebbles from alluvial deposits.

• Water Opal. Synonym of Jelly Opal

• Wax Opal. Yellow to brown Common Opal with a waxy lustre.

• Welo Opal. Opal from Wello, Ethiopia

• White Cliffs Opal. Opal from the White Cliffs, New South Wales, Australia

• White Opal. Precious Opal with light body colours (white, yellow, cream, etc.). Differentiated from Black Opal, which has a dark background colour.

• Wood Opal. Any Opal that formed a pseudomorph after wood from a tree and retains the original shape and appearance of the wood. Wood Opal may refer to both Common Opal and Precious Opal, but the term usually refers to large pieces of Common Opal.

• Yowah Nut. Small, rounded form of Boulder Opal from Yowah (Queensland), Australia in a nodules embedded in ironstone. Closely related to Boulder Opal, it occurs most often as walnut-sized ironstone nodules containing pockets, veining, or sprinklings of vivid Precious Opal.

Glossary of Opal Terms

• Amorphous. Shapeless. Not consisting of crystals. Non-crystalline. Glass is amorphous. Sugar is crystalline.

• Deflection. The bending of rays of light from a straight line.

• Diffraction. The Breaking up of a ray of light into either a series of light and dark bands or into coloured bands of the spectrum.

• Diffuse. To spread out so as to cover a larger space or surface. To scatter.

• Fluorescence. A light produced by the electrical stimulation of a gas or vapour. Fluorescent lights have a similar effect on opal as a bright cloudy day—they do not properly bring out the colours in opal .

• Hydrate. A compound produced when certain substances chemically combine with water.

• Incandescent. Glowing with heat (red or white-hot) as in a light bulb which glows white-hot, but produces a light that more closely simulates natural sunlight. Sunlight and incandescent lights bring out the natural colours in opal.

• Opal. Opal comes from the Latin word opalus, which means "to see a change in colour." Chemically, opal is hydrated silica, similar to quartz.

• Opalescence. A play of colour similar to that of an opal Opaque. Not allowing light to pass through. The opposite of transparent.

• Play of Colour. The way in which colours change as an opal is tilted in different directions.

• Silica. (Silicon Dioxide) A hard, white or colourless substance, that in the form of quartz, enters into the composition of many rocks and is contained in sponges and certain plants. The needle in the mouth of a female mosquito is made of silica. Flint, sand, chalcedony, and opal are examples of silica in different forms.

• Spectrum. The band of colours formed when a beam of white light passes through a prism or by some other means (e.g. mist or spray, in the case of a rainbow) The full range of spectrum colours are: red, orange, yellow, green blue, indigo, and violet.

• Sphere. A round three-dimensional geometric shape whose surface is equally distant at all points from the centre point.

• Translucent. Letting light through without being transparent.

• Transparent. Easily seen through. (Glass like)

General Glossary

• Amorphous - Having no definite form.

• Black Opal - Rare form of mineral opal found only in Australia.

• Cabochon - A gem or bead cut in convex form and highly polished but not faceted. Also, this style of cutting.

• Crazing - Tiny cracks on the surface.

• Crystal Opal - Transparent with flashes. Highly valued due to the brilliance of its colours and the fact that many layers of colour within the stone can also be seen.

• Crystalline - Composed of or resembling crystals.

• Direction - A measure of opal value.

• Dopping - Attaching a gem to a wooden extension by means of adhesive wax in order to polish or facet the stone with greater ease.

• Doublet - A manufactured opal gem consisting of two layers: Opal and obsidian or ironstone.

• Fire (or pinfire) - A measure of an opal’s colour or iridescence.

• Fire Opal - A translucent or transparent mineral opal found mainly in Mexico.

• Geothermal - Of or relating to the heat of the Earth’s interior. Many opals are found in ancient geothermal hot springs.

• Mineraloid. A mineral-like specimen without a crystal structure. Almost every opal is a mineraloid, not a mineral.

• Mohs Scale - A scale of hardness (measured by scratch-resistance) for minerals in which 1 represents the hardness of talc and 10 (sometimes 15) represents the hardness of diamond. Most opals are 5.5-6.5 on the scale.

• Organic Opal - An opal formed from the chemical petrifying of organic materials such as wood or seashells.

• Potch - Crusty mineral coating on naturally occurring opals. Also used as synonym for Common Opal sometimes.

• Quartz - A mineral SiO2, silicon dioxide, that occurs in crystals or crystalline masses.

• Silica - A mineral SiO2, silicon dioxide, that occurs in crystalline or amorphous masses.

• Synthetic Opal - Man-made gem opal.

• Triplet - A manufactured opal gem consisting of three layers: Clear quartz, opal, and obsidian or ironstone.

• White Opal - Common form of gem-quality opal, usually white or milky white in colour with bright pinfire flashes.

Opal Terms Used By Miners

• Agitator. Modified cement mixer used to wash dirt away from precious opal (see photo above.)

• Blower. A large truck-mounted vacuum cleaner used to suck dirt to the surface.

• Drive. A horizontal underground tunnel.

• Gouge. Mine slowly with a pick, nowadays usually only when opal is known to be present.

• Hoist. A bucket attached to a framework in a shaft, used to carry dirt to the surface.

• Level. Usually the layer of opal-bearing dirt.

• Muggie. A cheap solid opal, having little colour or brightness.

• Mullock Heap. Mound of opal dirt dumped by a miner on the surface.

• Nobby. Nodule of opal almost exclusively from Lightning Ridge.

• Puddler. Forerunner of the agitator, a mesh drum.

• Ratter/ratting. Thief/thieving from someone else’s mine (a serious offence).

• Rubs. Opal pieces initially shaped with waste material/sand removed but not yet cut and polished.

• Rumbler. Revolving mesh drum to sort opal from dirt, now superseded by the agitator.

• Shaft. A vertical hole down to a mine.

• Solid. A naturally occurring solid piece of opal, cut into a stone.

• Specking. Searching through abandoned heaps of opal dirt – also called noodling.

• Tail out. Search through tailings.

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

• Tank. Dam of water on which agitators are located.

• Windlass. Forerunner of the hoist – a hand-operated device for raising buckets of opal dirt to the surface by means of a cable around a drum with handles.