Fire Agate
By Bill Gallagher
Ok to reproduce with credit in entirety.
Fire agate is a combination of what many call Limonite, and Chalcedony Quartz. The so-called Limonite is actually Goethite, and that is the brown material upon which there are varying degrees of quartz deposited. The dictionary has this to say about goethite -- noun a dark reddish-brown or yellowish-brown mineral consisting of oxyhydroxide iron, occurring typically as masses of fibrous crystals. ORIGIN early 19th cent.: from the name of J.W. von Goethe + -ite. For the record, the iron content of good fire agate/goethite is such that it has a strong magnetic attraction, and can many times actually be picked up physically with some of the stronger rare earth magnets. When cutting fire agate all the chalcedony quartz is usually removed from the mass, leaving behind the brown layers where the actual play of colors, the fire, is located. Because of the proximity to the chalcedony, the goethite many times has some of the characteristics of quartz, as if it has been silicified, and that is understandable.
There is a lot of material in the west which has the exact same look as fire agate, with brown goethite with quartz deposited on it, but without the fire. The material which does have fire, that is, play of colors, is very rare, and the top grade is extrememly rare. Many times the rough commands high dollars by the carat, and that amont must be multiplied of course, because all fire agate rough is mostly waste, with just a small part of the rock being the actual gem.
In Germany there is found an irridescent Goethite, which seems similar to the Arizona material, but it is more massive, and not as bright, tending toward dark greens and purples, if my memory serves. Plus it is generally found without any quartz attached. I have not heard of any of that material being gem quality, but I am not a specialist in that material, I have just seen it in some rock books. The goethite of Arizona/California/Nevada/New Mexico and Mexico, which possesses a play of colors is aptly called fire agate, and seems to be found along a geological feature called the Colorado Plateau. It is sporadic in its occurence, and definitely a rarity, especially in Gem grades. Many times fire agate is found in little pockets amidst great masses of stone which looks like fire agate, but is void of any color at all, then all of a sudden will be a small area where the fire is present, and those are the mines.
The material is a byproduct of vulcanism, having formed within hollows caused by gas bubbles in molten rock, which were later inundated with water, flooded, in several separate steps. The age of the formation is not too well known, though I have heard 25-40 million years mentioned in several different places.
One of the best known places to find fire agates is in Deer Creek Arizona, south of Safford. There are many mines in that area, and some of the stone from there is world class. Slaughter mountain is nearby as well, Northeast of Deer Creek, and that is supposedly the finest fire agate in the world, although a couple of the California deposits are also considered to be of that same quality, most notably Opal Hill, and one called Oatman, or near Oatman. Near Safford but to the west slightly is the black hills collecting area, and I have first hand experience cfollecting fire agate from that locale, and though very sparse, some of the material is top notch. I have also found fire agate of high quality along the Pelloncillo Range in southern Arizona, North of Bowie. Finally, Agua Caliente, down in mexico, has produced some very bright and flashy fire agate, if you can get it.
When cutting Fire Agate it is best to do it with micro diamond tooling and witrh as much magnification as you can get. Make sure you take two Patience Pills as well. The fire layers within the goethite are most times very very very thin, and this makes proving the fire agate a lot of work, then the actual removal of waste is nothing but high tension stone carving, where even the littlest slip can damage the stone beyond usefulness. If you decide to take on fire agate, always buy the best quality rough you can afford. Even then it will be mostly junk, and there are many of us with experience in the cutting of thgis gem who will not even look at rough any more, because overall it is a much better deal to buy the finished product.
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