A stone cut into an oval, round, rectangular, freeform or polygonal shape with a flat (or slightly rounded) bottom and a domed or half round shape.
(Also known as potch) a piece of opal with no play of colors visible.
A term to describe a particular type of cracking within an opal. An opal may crack if exposed to the atmosphere and excessive drying takes place. This usually exhibits itself as hairlike fractures. An opal may also crack due to internal pressures which are released when cut.
A underground residence or dwelling (sometimes retail stores and churches also), in the Coober Pedy area, where about 1/2 the town of Coober Pedy resides. These homes maintain a constant comfortable temperature during the hot months of the summer (120-130 degrees F. not uncommon) and a warm environment during the cooler winter. Some of these homes are as comfortable as any modern home with sealed natural walls (to prevent dust and debris) or paneled walls and tiled floors. They have all the moden conveniences and some consist of many rooms.
Any near-horizontal structure continuously defined by tubule, gypsum, alunite and iron oxides, near a slide or fault possibly (hopefully) containing opal.
Waste rock or matrix (possibly containing useful precious opal overlooked by the miner) which is normally deposited above ground in a cone shaped pile called a mullock heap. Looking for precious opal in these mullock heaps is called noodling.
Pieces of round or nodular opal typically found in the Lightning Ridge area. The term is used to describe opal typically found in the Lightning Ridges area. These are the stones that fortunes are made of. It is unusual to find an uncut nobbie (with any promise) as a good nobbie may be worth up to $50,000 and many of these show no indications on the surface.
A number of people make their livings by just reprocessing the old mine dumps. They either sift through the waste dumps by hand or use one of the new noodling machines. This is a good occupation for tourists…be carefull of the open shafts…some are well hidden.
All hydrates of silica, SiO2.nH2O, including synthetic, natural precious and common opal but not imitation material; alternative term is opaline silica. Opal miners generally restrict use of the term opal to precious opal, calling material that does not show a good play of colors, potch.
(term used throughout the opal industry). A layer of precious opal, onto one face of which has been fixed an opaque base of natural or artificial material. The base is generally black to enhance the opal’s fire; it may be black potch, or more commonly a black plastic. Mintabie “semi-black” opal is a natural doublet.
An area of opal workings that lies within a declared Precious Stones Field, e.g. Olympic field, Stuart Creek opal field.
(term used throughout the opal industry). A solid piece of precious opal generally cut “en cabochon”, no other natural or artificial material is fixed to the opal to enhance its fire.
(term used throughout the opal industry) A thin layer of precious opal, onto one face of which is fixed an opaque base of natural or artificial material. Onto the other face is fixed a clear, domed top to magnify and also protect the opal. The better quality triplets have a clear quartz top, others a clear plastic top. Triplets can make use of very thin slices of precious opal which would otherwise be wasted.
In the Coober Pedy area this refers to a cigar-shaped, opalised fossil of a belemnite. In the boulder opal fields of Queensland a “pipe” typically refers to a vertical pipe-like deposit of precious opal measuring from fractions of an inch in diameter to several inches in diameter.
Applied to any opal the miners consider valueless, even though it may exhibit some color flashes. Sometimes opal with a few color flashes is called potch with color. There are many varieties of potch; jelly (clear and glass-like), white, milky, grey, blue, honey, black potch and chalky potch (soft, crumbly, white opaline silica). Geological definition – lustrous opaline silica with no play of colors.
Any naturally occurring opal exhibiting a play of colors. There are many varieties of precious opal, the names being based on background color and color pattern: Black opal – precious opal with a black or dark background color or blue, green, or brown. Crystal Opal – precious opal with a clear colorless background. Milky, grey and white opal – precious opal with milky, grey, or white background colors respectively. Semi-black opal – precious opal with a dark grey background. Mintabie semi-black is a white or clear opal with a natural backing of black potch. Harlequin opal – precious opal showing a regular mosaic-like pattern in rounded angular or roughly square patches of about equal size; them most highly prized of all color patterns. Flag opal (or flagstone opal) – precious opal with a color pattern resembling a flagstone paving. Pinfire opal – precious opal with very small or pinpoint sized specks of color. Miners’ term – opal miners generally restrict the term precious opal, or opal, to saleable precious opal. Opal that shows some color but is not saleable is called potch.
A layer of opal formed in a horizontal or near horizontal structure, either in a level or along a bedding plane. The layer of opal may vary in thickness from a fraction of a millimeter to over 100 mm.
(term used throughout the opal industry) Opalized fossil shell; there are two types: Skin shell – only the outer shell is replaced by opal. The space inside the shell is filled with sediment prior to opalization. Solid shell – entire body space is opalized, both the shell and the space inside. These terms are usually applied to fossil bivalves but are also sometimes used for gastropods, belemnites, etc.
Another term for a fossil Belemnite
Steeply dipping or vertical joint. Andamooka -rarely used, as little opal is found in verticals. Coober Pedy – generally infilled with red-brown tubule material, gypsum, alunite, iron oxide, or opal. This term is most often used to describe a seam opal deposit of precious opal that forms in a vertical plane. The fire layers most often form at a 90 degree angle to plane of the deposit or across the seam instead of with the plane of the seam. Mintabie – any near-vertical joint, the only discernible ones being infilled with opal, opaline silica or limonite.