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Opal Terms

  • Agate - Fine-grained with many colors of crystallized silica  and 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, a 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 can be seen within the stone.

  • 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 or seashells.

  • 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 opal.

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

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

a collection of our black and boulder opals

A sample collection of our black and boulder opals.

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