BOULDER - Opal found inside Ironstone. Found in Queensland
COLOR BAR - Layer of color in opal differing from color layers above or below.
CRACK - A crack in opal
FIRE- Opal with large areas of red colors.
FIRE OPAL - A term used for that opal where the base color has red or orange tone. This material usually comes from Mexico.
FLAW- Mark or impurity which devalues the stone.
FREEFORM- Opal that is cut to the natural shape of the stone.
GEM QUALITY - Highest grade opal.
HARLEQUIN - Very rare and most sought after opal, the colors form naturally in checkerboard pattern - this is a collector's item.
MULTI-COLORED - A stone that has more than 3 colors in it, but may have one color dominating.
MULTI-FIRE - A stone which has lots of colors without any particular color dominating.
NOBBY- A formation of rough opal occurring in Lightning Ridge - a round nodule.
PAINTED LADY - Exclusive to Andamooka - a thin layer of opal on hard sandstone, usually sold as specimens.
PINEAPPLE - Very rare collector's item - exclusive to the White Hills opal field in south Australia. A cluster of opalized crystals which are a pseudomorph of ikiate crystals.
PINFIRE- A pattern of tiny dots of color across the stone.
POTCH - Common non-precious opal without diffracted colors.
RED ON BLACK - Type of black opal which displays predominantly red. Extremely valuable.
REFRACTION - The deflection of a ray of light when passing obliquely out of a substance.
RIBBON- Pattern where colors roll in parallel bands across the stone.
ROLLING FLASH - Unusual pattern displaying colors which "roll" across the stone.
ROUGH - Uncut opal.
SEAM OPAL - Opal which occurs in horizontal seams; the most common type of formation: can be found in all fields.
SEMI BLACK - This opal has dark background but is not dark enough to be termed "black".
SKIN TO SKIN - A opal stone that has the color from the top to the bottom or all the way though, as all opal has a skin on the top and bottom of it from when it was formed millions of years ago, so if the opal is full of color between these two skins, we call it skin to skin, here in Coober Pedy.
SOLID - Opal that has no backing or man made additions. The natural colors are right through the stone.
TRIPLET ) - A thin slice of light opal attached to a black or dark background with a protective crystal or glass dome glued to the top.
WHITE OPAL - Opal that is mainly white with bright flecks of color.