Briliance - Refers to the intensity of brightness within the opal. The Better the brilliance the more desirable and therefore the higher the value.
Doublet Opal - A thin Slice of opal glued onto another natural stone. Unofficially there are two types of opal doublets mass produced that use the absolute bare minimum opal and hi-end doublets where the opal can be very thick
Fire - A short name when referring to the "play of colour" in an opal
Fire Opal - Has two meaning depending on where you are from. For us (Opal Museum Staff) a fire opal is a red coloured stone and inside the stone is the play of colour. This type of opal is from Mexico. Some people call an opal from Australia a fire opal if the play of colour is red and intense; we would refer to this same stone as it's type (i.e solid boulder opal with lot of fire).
Specimen - In general a specimen is a beautiful gemstone (often large and with inperfections) used to showcase the beauty of a stone in its natural form.
Loose Stone - Cut gemstone that can be used for fine jewellery.
Synthetic Opal - Created opal; has up to 20% adhesive inside to make it go hard.
Treated Opal - Sandstone containing opal has been cooked in palm oil and then the colour to be seen,
Triplet Opal - A very thin slice opal sandwiched between a quartz dome
Type 1 Opal - Classic Solid Opal. Is where the whole stone is either precious opal or a mixture of common opal (potch) and precious opal.
Type 2 Opal - Boulder opal. It is where the opal is a layer of opal naturally attached to the host rock underneath (usually ironstone). So it basically two stones ironstone and opal.
Type 3 Opal. - Matrix Opal. Matrix means to form inside of something else. So when we see a matrix opal we see on the surface of the stone a mixture of ironstone and opal.