76.6cts highly polished & untreated boulder matrix opal. 40 X 27 X 8mm. Field/origin: Yowah Australia. Colour: red, green, blue. Brightness rating 1 To 5. = 3.7. Pattern: Mesmerised unique one of a kind Pattern stone.
Unlike diamonds, all opals are distinctly different. Opal is a hydrated amorphous form of silica (SiO 2 ·nH 2 O); its water content may range from 3 to 21% by weight, but is usually between 6 and 10%. Because of its amorphous character, it is classed as a mineraloid, unlike crystalline forms of silica, which are classed as minerals. It is deposited at a relatively low temperature and may occur in the fissures of almost any kind of rock, being most commonly found with limonite, sandstone, rhyolite, marl, and basalt. Opal is the national gemstone of Australia. The internal structure of precious opal makes it diffract light. Depending on the conditions in which it formed, it can take on many colors. Precious opal ranges from clear through white, gray, red, orange, yellow, green, blue, magenta, rose, pink, slate, olive, brown, and black. Of these hues, the black opals are the rarest, whereas white and greens are the most common. Opals vary in optical density from opaque to semitransparent and show opalescence, a form of iridescence. There are 9 separate factors that contribute to the price of an Opal. These factors are: 1. Color 2. Direction / Play of Color 3. Pattern 4. Body tone 5. Brightness 6. Shape 7. Inclusions 8. Where the Opal was mined 9. Country of Origin At Lightning Ridge, in Australia, a committee values opal miner’s opals each Saturday. Several opal appraiser price each opal by carat with the final value determined by the price per carat. COLOUR In order of evaluation value, the most valuable color is a dominant red, then orange, green, blue and purple. Electric blue Opals is the most valuable of the blues. DIRECTION OF COLOR Opals are a gemstone that dramatically change appearance based on the angle of view. When an Opal is at it’s brightest, this is called its ‘facing’/ andle. The direction of color will affect the price because it determines how versatile the Opal is. PATTERN Opals that have a rare or unique pattern are more valuable. The Harlequin patternis the rarest and most loved pattern in opals but it is very rare. A True harlequin pattern is a mosaic broad pattern, angular close set of colors. Floral patterns are sometimes called floral harlequin.Some top patterns are Mackerel, Block, Broad flash, Rolling-flash, Pin-fire, Rainbow and most sought out Ethiopian opal is the Honeycomb pattern. BODY TONE Opals are grouped in 9 sub categories N1 to N9 with N1 the darkest opal and N9 the lightest. Black opals are generally the most valuable and have a body tone of N1 to N4 ? Opals with N5 to N6 considered a semi black or dark opal. ? Body tone N7 to N9 are called crystal opals. BRIGHTNESS The Opal brightness guide was produced by the Australian opal association along with the body tone guide. There are 7 sub Brightness ratings with B1 the brightest to B7 the dullest. The brighter the Opal, the more expensive will be its value. SHAPE Oval stone are generally considered more valuable than free form, except with boulder opals where free form is considered desirable. The shape of the Opal once again determines how versatile it is. Oval stones generally have the best face of color and can be used in a variety of applications. Opal is almost always cut in a cabochon. A cabochon stone is more valuable when it has a high. This is due to the fact that cabochons make ideal ring stones. INCLUSIONS Inclusions and potch lines and are not to be confused with cracks. A crack line reflects light and greatly devalues an Opal. A potch line has no light reflection and these opals are generally valued lower but can make artistic picture patterns. Some Opals will have a vegetation pattern from the inclusions and this is popular as the opal has replaced some of the tree or vegetation. Sand or windows also reduce the value of the opal. A window is a gap on the bottom where potch has not formed and opal is transparent. Ethiopian opal can have a ghost or phantom inclusions or vegetation matter. These types of inclusions are generally accepted as reasonable in this type opal. OPAL FIELD SOURCE The end buyer or wholesaler might not be able to consider this factor. But in the trade certain mines have a reputation of producing good quality rough that makes excellent stones. This happens in Australian and Ethiopian opal fields. Even the depth of the mine can greatly effect value. Opal doublets and triplets do not have the same stringent criteria as solid opals and are valued considerable less. It is important to be able to pick a doublet opal compared to a solid and this can be difficult when the opal is set into jewelry. COUNTRY OF ORIGIN Australia has a worldwide reputation as the world’s most expensive opals. Many countries now produce good opals like Ethiopia, Mexico and Brazil. Each country’s opals may be unique and this factor helps determine the Opal price. Regardless of the country of origin, all opals are rare, valuable and unique. Opal Stones rank very high as an appreciating asset.