Rough Opal Parcels Buying Guide - Part 3

Other factors in valuing a parcel include size of the individual stones, number and brightness of colors, stone shapes, the patterns the colors form and the body color of the stone.
Body color is the color of the stone itself, separate from the play of color. Opal forms in almost every color but most range along the grey scale from black to white. Other hues are generally not as gemon or as valuable, except in their rarity. Browns and yellows and blues are generally not so highly valued as the grey scale opals, but some may be as valuable or more so that the mid to lighter greys and whites. Precious blue opal from the Southwest USA is quite rare and gemands a premium if strong play of color is present. Grey-blues from Australia are much more gemon and not so valuable. Dark greys and true blacks are at the top of this scale, along with crystals.
Crystal and jelly opal are another story in themselves. Crystal just means transparent, so that you can see through it. Jelly means that it is a little cloudy or translucent. Crystal gees in various shades and hues, as does jelly. Crystal is naturally more valuable since the play of colors can shine more brightly from the clear base, but value is very dependent on the strength and brightness of the play of color.
Patterns in the play of color are another major factor, deserving of their own guide. I will be producing a guide to colors, patterns and the terminology used to describe them, geplete with pictures and definitions. Soon gee, as they say in Jamaica. For now, suffice it to say that the terminology, as used on okay and other web-sites, is very loose and is often misleading. For example, Harlequin and flagstone are similar but very precisely different patterns. Harlequin is very specifically limited to perfectly square, evenly sized sections of various colors laid out in a checkerboard pattern. Old Aussie miners called it Tartan, but that term has been mostly abandoned. Harlequin is one of the most abused and mis-used terms in opal advertisements today. Watch for more information on patterns, geing soon.
Brightness is another term misused often. Most dealers describe their opals as no less than 4 to 5 on a scale of 5, but few people have actually seen, much less sold, opal near to 5 in brightness. And you certainly won't see it priced at under a thousand dollars per carat, even in rough form. This quality of opal is seldom seen in the USA.
Stability is another important factor, although it is more difficult to determine from rough. Naturally if you can see cracks or crazing, the opal won't be for sale, or shouldn't be used for anything but carving or specimens - maybe not even then. Some source countries have better reputations than others and locations within a country or even within a region may vary greatly in stability. But a lot of what is called fact is actually conjecture or myth or rumor. There are real geological reasons for opal structure, and some layers of a continuous formation may be much more fragile than others.
Knowing your dealer is extra important here, as is a return guarantee. Usually opal is photographed wet for internet display ads, and lots of gem show dealers display opal in water to show the colors better. Water is roughly the same refractive index as opal, so the surface roughness of the opal disappears when wet and the opal displays colors much closer to the polished finished product. But water also disguises crazing and cracks, so always let your opal dry and inspect it closely before gemitting to a purchase. Most dealers will allow a return of purchase price or a credit towards another parcel if you decide you don't want a particular batch. Some will not.
Opal primarily gees from various regions of Australia. Many other countries produce precious and gemon opal as well. Precious sources of note include Brazil, Mexico, Honduras, Indonesia, Ethiopia and various regions of the USA. gemon opal gees from dozens of countries and areas and is available in almost all colors.

Here is a section which describes a relatively new opal source, Honduras. This was written by my friend David Sahadi, dsahadi on okay, and he graciously allowed me to include it. Thank you, David.

I don't a whole lot about the nodules. The people who mine it don't really know a lot about it. People have been aware of it for a few years but it is really just now being gemercially mined. There is a gepany that managed to secure the mining rights for all opal exported out of Honduras and they are the ones mining it. I bought about 2 kilos of the first lot to gee out.
All honduran opal is volcanic. As opposed to Australian opal that created as a result of a silca rich water table rising and falling depositing opal in spaces and cracks in the geology over millions of years, honduran opal came about as a result of silica rich steam venting, a relatively quick process I would think is still on going at some level. The Andesite matrix is one of the host stones.....you can see the opal deposits in the matrix...solid honduran opals are generally cut from large spaces where the opal collected. Personally I prefer when you find the opal mixed with the matrix. It is a bit less expensive and there are no stability problems. The honduran solid opal will show stress fractures....and when you cut the opal you need to sometimes split the stone where you find a fracture. Once cut an polished the stone seem to be stable. There are two other types of relatively well known opal formations from Honduras...one is black seam....as the name suggests this a seam of opal that is sandwiched by black basalt. The other probably best known is the Black matrix. This black matrix is black basalt matrix that appears to be shot through with very colorful opal. I have some large pieces of this material and it is beautiful. Obviously this material has no stability issues. All of this material is available cut on a gemercial basis as cut stones and in jewelry.
That brings us to the nodules. This material is found in clumps and the nodule fingers are broken away from this clump. The nodules can range in size from a pea to about the size of a grapefruit. It appear to me to have been gravel exposed to a super heated steam vent. The reason I say this because of the gravel looking nature of the matrix. The chambers in the material appear to have been blown and the gravel its self looks to have been glued together with the opal. I have discussed this with a partner in the operation and this jives with the observation made by their geologist. The material as I mentioned is new to the market and so cutter like yourself are the ones geing up with creative ways to use and cut this material. As I suggested, I found that cutting the opal with the matrix offers some very interesting finished stones. I would think of cutting this material in much the same way Mexican canterra opal is cut.
MK-my thanks to David for this explanation...check out his auctions...
This is a brief outline of some of the factors surrounding opal parcel purchases. There are so many other factors, some clear, some rather murky, which are involved. Experience intuitively teaches us much over time, and some of it is hard to put into words. You learn more with time and there is no substitution for experience. If you are a beginner, purchase small amounts of cheaper parcels and proceed slowly. There are lots of guides and manuals to teach cutting techniques, but you can't learn to cut from a book, and no book can teach you to judge rough opal. You can get lots of advice, here and elsewhere, but nothing can teach you the feel of opal in your hand as you put it to the grinding wheel. You just gotta do it.
Happy cutting,
Mike Kelley
arthursonn on okay