- Agate - Fine-grained
variegated chalcedony with banded, striped, or mosslike coloration.
- 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 colors and the
fact that many layers of color 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 color 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.
- Mohs' Scale - A
scale of hardness for minerals in which 1 represents the hardness of talc
and 10 (sometimes 15) represents the hardness of diamond.
- Organic Opal - An
opal formed from the chemical petrifying of organic materials such as wood
- Potch - Crusty mineral
coating on naturally occurring opals.
- 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 whit or
milky white in color with bright pinfire flashes.