Opal Parcel Information

A rough opal stone, or opal rough, usually consists of a combination of several materials. These are matrix, potch and precious opal.

Matrix is the non-opal stone in which the opal was deposited, and from which it was mined. This is the "host stone" for the opal. This may be any one of various materials, depending on the source of the opal. This material may be sandstone, ironstone, rhyolite, andesite, quartz, basalt or any number of other minerals. Usually most or all of this is trimmed away in the opal cutting process, so the ratio of opal to matrix is an important factor in purchasing rough.

There is a variety called matrix opal, in which the opal is in very small or fine particles mixed throughout the host stone, so the entire piece is polished and the opal sparkles are sprinkled across the surface of the stone. The important factor there is the concentration, brightness and colors of the opal particles.

Another factor is the beauty of the matrix host stone. Often the matrix is treated to darken it for a brighter relative display of the opal particles. This sort is often treated with a sealer material to produce a smoother surface and better polish.

Some opal material is cut leaving just some of the matrix showing in the finished stone. The opal may be in large nodules, surrounded by the matrix. This is often cut in a window style, with a bit of the matrix left around the precious opal.

Potch, or common opal, is solid opal of any color which does not show the sparkly play or apparent movement of color as the stone is moved. Opal potch may come in almost any color, and some is quite attractive if polished into a cabachon. If transparent, it may be faceted as well.

There is a variety of common opal which is considered separately. This is known as fire opal, a rather loosely used term which should truly only refer to clear or translucent material in the yellow to orange to red color range. The term fire refers to the color of the body of the opal itself, thought of as the color of flames. Many times, any opal with a play of color is referred to as fiery or fire opal or as the fire in the opal. This is a common term for the play of colors seen in opal, so confusion abounds. Nonetheless, true fire opal is a variety of common opal described by color and transparency.

Precious opal is opal which shows a play of color in some pattern which changes as the stone is moved. Naturally, the brighter the color and the more colors present, the better. Varieties of pattern and relative worth of colors and patterns will be discussed below, along with a discussion of the various body colors, the color of the stone separate from the color and brightness of the play of color.

Mike Kelley - arthursonn