Buying opal rough

Opal rough is like any other gemstone rough. Thereare high grades and there are low grades. What you see in rough on okay is the lower grades. The high grade rough is either already contracted to or being held for the big oriental buyers. This hasn't changed and okay never really touched that market.One thing I've noticed on okay is the lack of proper terminology with opal. Many dealers are calling any kind of opal "fire opal". This is a term that has always meant the translucent to transparent opals of red, yellow-red, or orange color, mainly from Mexico, but can be found elsewhere and does not have anything to do with plays of color. These dealers exhibit their lack of knowledge with opals and use it to describe opals with plays of color. This is precious fire opal when it meets the base opal color and has plays of color.For terms used to describe opal and used in opal mining check this website out: http://www.imagineopals.ge/terms.htm
You can find great material in the lower grades, material that will bring a couple hundred a carat even. But high grade material starts at these prices and will parallel diamond pricing on the high end per carat.
The biggest single problem with buying opal on okay is the people with more money than sense. Those people that have to keep bidding and being on top and the current high bidder no matter what.
Sellers lovethem and will consistently list rough opals and rough opal lots to lure inthese bidding addicts.
The value per ounce is variable and covers the range from potch with no or little color to nice material that has edge to edge (or skin to skin) colors. So, there is something for everyone's taste plus practice material. If your new to lapidary, you'll be sure to want to get some practice material because you just have no idea what it's like to grind through the color layer and discover there really isn't more color underneath.
Pay attention to shipping costs and understand that even though you are allowed to return material you feel isn't up to what was described, you will have to pay for shipping and most often, you will not get any shipping refunded.
Buying Australian opal from a miner or the friend of a miner is pretty good, but also realize these miners work the mines and so, your order might take a little longer to arrive. Those brokers who sell for miners generally get items sent out pretty quickly, but shipping from Australia is going to take longer than local shipping and it costs more.
You also have no clue as to stability of the rough you are buying when you buy from a miner. The miners only have a general idea of any material they have just mined and cannot say for sure if a piece or lot from a seam is stable until they have let it set dry for a period of time. What they do know is that similar opal from opal found in the same mine was stable or not, or from the area they are in does such.Another item to be wary of is "rubs". Rub are "windowed" and sometimes polished (all rubs used to be polished but times change) stones. This was most helpful for nobbies from Lightning Ridge as often, clipping would only show a hint of what might be below the rough coating. Beware though of rubs that show lots of color, here the questions to ask are, how much "color" has the preparer gone through and how much color has been left to work with. This may mean the difference between a solid and a doublet. Big dollar difference in the value of the final piece too! Most opal cutting guides would have you stop "exposing" the color layers as you just approach them so that you can change to a finer grit wheel and move more slowly. Buying a fully exposed piece (just cause the preparer wants to entice you with how much color there is) may leave you spending your money on rough which will not return your investment. A true rub will expose a small area of the stone, quickly polish it and let you decide on the ability to take it further. In most cases, this was how parcels were sold. Today, with the direct from the mine to the end user, I am not so sure this is happening. On opal which is not a nobbie, and gees from a seam, maybe one small stone could be processed to show the quality. When all the stones are processed, you could be walking into a mess with a preparer who isn't selling with a opal cutter in mind or maybe the preparer isn't even a good cutter at all and doesn't know what to do. Ask lots of questions!!!!
Mexican opal is funny, it could craze after a year of being dry and worn in a setting. But we don't know the conditions any jewelry or rough goes through unless it's our own. And even then, unless kept in a specific and constant environment, even we can't be 100% sure. Mexican and Virgin Valley opal is known for it's cracking and crazing upon removal from water and drying out. The old miners at Virgin Valley would put their opal on the tin roofs of their sheds and if it hadn't cracked after a day in the sun, they felt it was stable!
Virgin Valley opal is some of the best though for colors.
Honduran matrix opal, that black matrixed material with the micro specks of colors isn't pure opal. It has a black, porous matrix which is filled with the opalized skeletal remains of micro marine creatures. This matrix needs a resin sealer to allow really nice polishes.
There is alsoseam and boulder opal geing from the Andes(I haven't visited these regions and can not gement on the mining practices other than they use explosives to mine the Mexican opal out of the rhyolites I've read), but my experience with andesite entrained opals is that the andesite doesn't give up it's prizes nearly as easily as rhyolites do. There is no reason to expect any less colorful material from these places as is found in Coober Pedy. Just don't expect to see the good stuff.
British Columbia, Canada has precious opal regions. Some of which is marketed. Much of it I went to dig for is a boulder opal covering a volcanic tuff. There are solid nodules here that will cut really nice gems, but they are rare gepared to the precious covering on the volcanic rock. There is also a facetable dark honey opal found in this rock, again, it is found in the cracks and voids within this rock. You do have to let it age well before cutting to be sure your going to have something when your done faceting it. It can be unstable. The seam or boulder opal from these places has a tendency to be hydrophane opal, and most except the solid nodules and seams pieces are treated to either hold them together or preserve the colors or both. This opal I haven't seen on okay (it may have been put up but I didn't see it). I have seen some of the gemon opal which tends to be a pale green or blue.
Oregon opal shows up more than Idaho does, both of which can be great stuff to work. They also can be unstable. Louisianan opal is hard to get as the land is owned by one of the major lumber firms and they will not allow mining, yet. What is available is either old stock or poached.
Ethopian and other opals are also available on okay and the web. Choose with care who you buy from. Check for others who have bought from these sellers and read the sellers feedback. I've noticed fractures in this type of opal offered on okay, so buy with caution. It's mostly caused by cracking open the nodules to see if it's worth while.