Out of the Rough comes some Treasure

Here is a picture of some cut-offs from the 3,000 carat parcel of rough fire agate that is being cut as I type. Congratulations to the lucky eBayer that got the first beautiful 3-carat stone out of this parcel! Note the cutter’s ink is visible, revealing a bit of his planning.

Fire agate has a natural beauty that defies comparison. This is an exciting stone with a great future and it is a value when you consider the rarity, difficulty to cut, and the serious lack of quality cabochons on the current market. I am fortunate to have a true expert cabochon cutter here in Chanthaburi whose experience running a production shop in Singapore has given him the knowledge needed to cut this difficult material.

Don’t take my word for it when I say this stuff is hard to cut- just look at all of the tumble-polished pieces online! Part of the story is weight-retention as tumbling to finish and then polish the surface retains maximum weight. But these sellers know that their per-carat prices and their overall revenue and profit would increase if only they could cut it. If only! Many back-yard lapidaries have failed in this endeavor and even as Melanie and I move toward producing more finished stones from rough material I will keep my cutter for stones like this.

Part of the problem with fire agate is the structure. You have to know a little about how it is formed to get the picture so I will try to explain it. As hot water (heated by natural volcanic processes) rich in silica and iron is deposited in voids in rock, it leaves behind a small layer of quartz and iron oxides as it leaves the same void. A void fills and empties many times as a fire agate is formed, and each layer has similar chemistry. This is essentially chalcedony forming in layers through which light can pass. But as light passes through these layers, it is separated in much the same way that a prism separates the different colors of white light.

Here is the gink- the deal- the catch. The void is dry between fillings of this hot silica/iron liquid. It can fill with debris that is vaporized by subsequent hot fillings, and that vapor can be deposited between the layers of chalcedony. If you have pure water with only iron oxide and silica each and every time, and it fills that void at precise intervals and temperatures, and is safe from any impure intruder- then fire agate would be easier to cut. The layers would not want to separate and the rough would be much easier to predict. But nature is loaded with impurities and with variations in temperature, chemistry, and things do not happen to a set timetable. All of these factors reduce fire agate’s homogeneity, and increase the difficulty that lapidaries have with it. And remember often the cutter gets a touch to close to a gorgeous bubble of color only to find that it has disappeared in the next sanding! Could anything be more frustrating?

I will not know the final yield until this parcel is completely cut, but as expected it is very low. Some cutters try to keep 40% of their weight when they cut cabochons, the finished product be darned. I have my cutter take away everything that is not beautiful and yield be darned. I can see from the little that is finished that in spite of very low yield this material from Calvillo, Aguascalientes, Mexico lives up to its reputation for quality. These stones are absolutely stunning and the variety over such a small lot is incredible.

One of the rarest types of agate is sagenitic fire agate. It contains sprays of needles and also shows the interference colors that make fire agate so beautiful in an opal-esque way. It’s unreal that I did happen to get one of these cabochons out of the lot that I bought, but it is currently on offer to a dealer so I can not show a picture here. Let’s hope he turns it down, because my price was far too low!

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