Here are the latest samples of black opal rough on auction:

	BLACK ROUGH RUBBED BY MINER N2 26.70 CARATS JO 86 opalplus	50.00	-	-	1 minute 53 seconds
	BLACK ROUGH RUBBED BY MINER N2 2.30 CARATS JO 87 opalplus	25.00	-	-	1 minute 53 seconds
	BLACK ROUGH RUBBED BY MINER N2 8.25 CARATS JO 89 opalplus	50.00	-	-	1 minute 53 seconds
	BLACK ROUGH RUBBED BY MINER N2 2.90 CARATS JO 90 opalplus	30.00	-	-	1 minute 53 seconds
	BLACK ROUGH RUBBED BY MINER N2 3.80 CARATS JO 94 opalplus	15.00	-	-	1 minute 53 seconds

It’s interesting to watch the beautiful play of color on these opals. If you have friends who don’t know what opals really look like or what play of color is, show them this video.

Watch this video to find out.

However, even this boulderless-opal found buyers. According to the book Opals by Fred Ward, these opal first appeared in 1873 at a London gem exhibition, and were so successful that several leases, mines and sales were documented between that year and 1888.

Ward gives Tully Wollaston credit for introducing Queensland sandstone opal to the rest of the world. In 1888, Wollaston set out for Queensland with two other men, to find Joe Bridle, the first miner who found these opals, apparently. Wollaston purchased all he could, then took the material to England to sell. It took some persistence in the face of rejection, but finally some London jewelers purchased the material, and the market expanded rapidly after that, for a number of years – before the other opal fields in Australia made their debut.

Sandstone opal, which is also found in Mintabie and Andamooka, forms opal that is unattached, whereas boulder opal is formed attached to ironstone.

Australian gem associations define boulder opal in this way:
“Boulder opal is presented in one piece, where the opal is naturally attached to the host rock in which it was formed and the host rock is of a different chemical composition composition.”

The earliest miners would cut or break the opal away from the ironstone, and would then sell it as Queensland Opal. If the opal broke when it was being separated, it would simply be thrown away.

It was not until the 1970s that boulder opal found a market. Today, the best pieces of boulder opal can fetch as much high prices as even black opal.

If you want to teach yourself how to cut opal, you will of course work with the least expensive varieties of opal rough, before you move on to the good stuff.

How do the professionals do it?

Opal miners sell their rough opal as parcels. Potential buyers sort through these, and it is their skill to decide how many precious opals can be cut from each piece.

There is never any guarantee as to what the eventual outcome will be, of course, which makes the life of an opal buyer an exciting and tense one.

The opal cutter uses a diamond saw to cut the rough opal into ‘rubs’ (opal in the rough shape of a stone). During this process, excess material such as “cracks” and “potch” (colourless opal) is removed.

The opal cutter must ensure that he (or she) keep the stone as large as possible, whch at times can be dfficult and calls for great skill, since each act of cutting reduces the size of the stone, obviously.

Because opal can burn or even crack if subjected to extreme temperatures, water must always be used when cutting, to avoid overheating due to friction.

When an opal is burned, that means its surface becomes pitted – no more smooth surface or polish.

To that end, there are a variety of instruments one can purchase.

Readers of this blog in America can purchase a rock tumbler from Amazon.com:

and if you want to learn how to cut opals and other gemstones, there are of course a few books on the subject:

Amazon.com UK also has a variety of products for sale: Rock tumbler and other material.

And of course, such material can be purchased at your local gemstone store, or via the various gemstone magazines.