Fire Agate International

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fired up - by Jim Watson & Mike J. Galesi
  

"Fire agate is a stone of hidden beauty," says lapidary Jim Haufmann. "There's a cap on the color, really. It's grey or white on top, brown underneath, and you never know what's inside."

Kaufmann, well known for his intarsia designs, has found the beauty in fire agate and flaunted it in several recent works, including an award-winning intarsia-framed mirror.

The range of colors makes fire agate a lovely gemstone, but the color patterns within the stone can be equally important. Colors may appear as tiny pinpoints, or as bubbles, bull's eyes, flashes, specks, swirls, or a combination of these. If you add shape as a factor, the combinations are endless. Each fire agate gem becomes a unique, natural creation of color in three dimensions.

"I especially like the depth of field within the stone," Kaufmann notes. "Few other stones have that, but opal does, and I like to combine the two-opal and fire agate-for that reason."

An article written in the 1950s states that fire agate was known early on as "opalescent agate," "cinnamon opal," and "precious peacock stone." The similarities between fire agate and gem opal are immediately evident. Both gemstones are cut en cabochon and reveal a play of color, sometimes showing many colors within one stone. Common opal is often associated with fire agate. Curiously, we have seen pieces of fire agate-from Spring Mountain, Arizona, for example-with precious opal attached. One Aguas Calientes locality in Mexico is marked by a road cut below the mining pit that has precious opal in it. Some people have even suggested that opal evolved into fire agate, but we have not come across support for that idea.

Upon closer examination, fire agate and opal are as different as they are alike. Fire agate, composed of cryptocrystalline silica rather than a non-crystal line form of silica, has a superior hardness (about 7 on the Mohs scale), as well as a superior toughness. This makes fire agate a much more durable gemstone, "great for jewelry," says Kaufmann. Also, because it is not a hydrous silicate (as is opal), fire agate will not crack, craze, or fade. Both gemstones are pseudochromatic, meaning that the color is not due to atomic structure or chemical composition. The colors in fire agate are due to numerous, very thin layers of iron oxide within chalcedony. The iron oxide was deposited on botryoidal chalcedony and then these mounds were covered with layers of more chalcedony. A Florida University team has determined that fire agate's colors are transmitted through a process known as interference, the same mechanism at work when we see oil on water. Interference is caused when thin, orderly arrangement of lines, platelets, or surfaces causes light beams to interfere with each other, causing color patterns known by physicists as Newton's rings. Some research has indicated that the iron oxides (probably goethite) within the chalcedony do not actually cause the color; the research points instead to the arrangement of tiny silica platelets that were influenced in their formation by the iron oxides. However, the role of the iron oxides in the interference process is still uncertain.
  

  

Opal, on the other hand, produces its colors mainly through diffraction. This occurs when an orderly arrangement of cristobalite (silica spheres) within certain size limits diffracts light in an organized way to spread white light into its various colors. This difference supposedly allows opal to produce truer primary colors, and therefore brighter colors, than those seen in fire agate.

Fire agate also differs from opal in that it is not found all over the world. Because of its limited occurrences, we don't think it will ever be a major gemstone-but that's okay with us! The hunt is what keeps us interested. Not only is the fire within stones somewhat elusive, but so is the fire agate itself. We have heard that a lot of the Mexican fire agate has been depleted; you have to go down deep to get it now. This may be it-pieces we sold years ago we wish we could have back now.

The followers of fire agate are few, but all of us are totally hooked. The Watson part of this writing team for example, has collected minerals since childhood and got his first look at fire agate in Tucson a few years back. It was the first stone he tried his hand at cutting-a real baptism by fire. The Galesi team member had sculpted marble and alabaster previously and started off ruining a few pieces of these bizarre new rocks he got from Watson. He's been hopelessly sidetracked ever since. When we're not busy chasing after fire agate, our passion, we install pools (Watson) or work at music production and commercial real estate (Galesi).

In all, we're a small circle of crazy people who sometimes get together and trade fire agate like baseball cards. We keep track of every stone-the stones we had in a ring might have been put in a pendant later, then simply became part of someone's collection. Even if fire agate were more abundant, we would still be bartering quite a bit amongst ourselves, because so many jewelers like calibrated stones just is not going to happen with fire agate.
  
  

Points Southwest.
  

  

The world's only known fire agate deposits fall within two general areas-the Sonoran Desert region, stretching from southwest United States to northern Mexico, an area starting 100 miles north of Mexico City and lying between two north-south mountain ranges, the Sierra Madre Occidental and the Sierra Madre Oriental. These areas were subjected to extensive volcanic activity mostly during the Tertiary Period, 24 to 36 million years ago, relatively recent by geologic standards.

Everybody and their grandfather claims to have discovered fire agate. "According to Warren Jones, fire agate was discovered in Arizona in 1939," say Si and Ann Frazier, Lapidary Journal Foreign Correspondents. "In an article he penned back in 1977, Jones states that he began to work it in 1941. He claims to have discovered Mexican fire agate in San Luis Potosi in 1961 and to have mined tons of rough material over the years, a claim that may be only slightly exaggerated. We listened to Jones describe his adventures with fire agate many times, and we purchased many pieces of fire agate from the Venice lapidary guild, a sort of hippie cooperative commune Jones set up in Venice, California, in the 1960s."

The fire agate appearing early on was generally poorly cut, because most of the stones were worked on flat grinding wheels and sanding belts by cutters who had little or no experience with the stone. Also, the stones were cut into simple cabochon shapes, even calibrated sizes, and there was a tendency to keep them thick to add carat weight. The results were nicely shaped but low-to-medium quality stones, containing areas with no fire or poor fire orientation. Nonetheless, some truly fine gems did appear, sparking interest among cutters and collectors.

In the United States, good quality fire agate was being mined in the Mule Mountains near Wiley's Well (also known as Coon Hollow) in Imperial County, California. Fire agate was also found in northwestern Arizona in several locations, including the Oatman Gold Road Mining District and at Spring Mountain, in the Black Mountains north of Oatman. It was also found in the Little Horn Mountains, 35 miles east of Quartzsize. In southeast Arizona on the north slopes of the Galiuros Mountains, an area known as Deer Creek, 40 miles west of Stafford in Graham County, became a good producer and a number of claims were filed.
  

  

A short distance northeast of Deer Creek, a very rich fire agate deposit was discovered on San Carlos Apache Indian Reservation. At this location, known as Slaughter Mountain, only tribe members are permitted to mine, and no blasting or heavy machinery is allowed. Our own experience with mining fire agate has been in weathered rhyolite, from which it is fairly easy to remove the material. But at Slaughter Mountain, the matrix is less yielding rhyolite, which makes getting the fire agate out like chiseling a Coke bottle out of cement. Other locations include Saddle Mountain near Phoenix and the Day Ranch between Bowie and Duncan. Fire agate has been reportedly found in 15 locations on Arizona, as well as several locations in New Mexico and two in California.

Pinfire and Peacock. The colors found in fire agate cover the entire spectrum. Orange is by far the most common color, followed by green and purple. Yellow, often seen in combination with other colors in fire agate, almost never occurs by itself. Red and blue are the least common colors. Usually, the color red is actually an orange-red, and blue is a combination of purple and green layers appearing to be blue. When viewed under magnification, this becomes more apparent. Certain color combinations in one stone are especially pleasing, such as purple and green or, more rarely, yellow and blue. When a stone contains three or more of the artist's primary colors, red-yellow-orange, green, and purple-blue, the highly desirable gem is called a "peacock".

A general rule to color in fire agate is this: The upper layers of color usually show orange, red, or yellow, followed by green, then purple and blue. But exceptions to this general rule abound. On rare occasions, if the stone is cut just right, it will display all the colors of the rainbow in sequences.

The color layers are very elusive-like breath on a pane of glass. You need to polish before you get to where you want to be or you will lose the color. But if you use skill and imagination to follow these layers, you will maximize the beauty of the stone.

We are very familiar with Deer Creek material, since we bought into the original claim at this locality a few years back. The colors we see at our mine are green, purple, and blue. But just a quarter of a mile away, red, orange, and green are the colors found. You might say that the two mines comprise a valley of rainbow fire.

The fire at our claim, or any other mine, is not immediately apparent. The fire agate is brown, the rock is brown, and the white chalcedony shows up only after it is washed off. We have three holding ponds, which collect rainwater for washing materials, with a growing rubble pile in between There is so much rubble after 30 years of excavation, but a two inch pump allows us to hose off the rough. It can get very muddy; we once had a bulldozer stuck up to the cab.
  

  

At Deer Creek, it seems the deeper we go, the less color we find. Still, whenever it rains, we can go out there and pick up good fire agate right off the dumps, spotting material we missed when everything was dry.

Each fire agate deposit produces stones with particular characteristics. Someone with a good knowledge of this gem can usually look at a finished stone and be able to tell the locality from which it came. For example, one deposit in Mexico near San Luis Potosi produces stones with a mirrorlike or metallic look that is very unusual. These stones are especially bright when viewed out of direct light. The rough from the mine exhibits a black rather than the usual brown body color in the chalcedony.

Mexican fire agate from some of the mines of Aguas Calientes in the Central Basin, tend to produce stones with color layers that are flat or sheet-like. These stones are naturally easier to cut, especially if the fire layers are thick. This material is better suited for slicing for inlay work than stones from Deer Creek, which tend to be more botryoidal in form. Stones from Slaughter Mountains are somewhere in between. Also, Deer creek material tends to be less directional, that is, the color does not fade or disappear as the stone is turned.

Sagenitic sprays, or needlelike formations within the layers, occur in fire agate from all deposits. Little is understood about their formation, but these "inclusions," mores common at Deer Creek, can enhance the beauty of a gem by creating a beautiful spray pattern within the stone. Jim Kaufmann likes to find small sagenitic sprays for his intarsia work. "A lot of it can be overwhelming," Kaufmann explains, "and can make the design too busy, but little starbursts are very pleasing."

Fire agate from Slaughter Mountain has everything found at other sites plus a few peculiarities of its own. Some stones display an added three-dimensional effect with one color layer appearing to "float" on another, separated by the clear chalcedony between them. This is noticeably absent in Deer Creek stones, we have found, but does occur sometimes in Mexican material. Another characteristic of Slaughter Mountain stones is what we can only describe as the "crackle effect." This is when the finished stone displays internal fissures of color, something like cooling lava. Upon close examination, it looks like stress cracks within the fire layers. Some Mexican material displays this effect, and to a much lesser extent, Deer Creek fire agate does, too.
  

  

"Pinfire" is a phenomenon found in all fire agate, especially the stones collected at Deer Creek. Pinfire gemstones consist of hundreds of tiny bubbles of color. When the background is dark, it appears like stars floating in the universe. The botryoidal formation that produced the bubbles and pinpoints in fire agate can be utilized by the lapidary to create unique features, such as "eyes," step cuts, and interesting designs or patterns within the gem.

Another interesting and beautiful occurrence in all fire agate is known as a "reverse" or "negative." Fire agate tends to be convex, so when the underside of the color formation displays concave fire patterns, it is known as a reverse pattern. Often this gives the appearance of the fire moving across the surface of the gem as it is moved. A reverse is often created by chance when the underside of the cabochon is trimmed or ground flat. Sometimes a double-sided gem can be created this way.

In five or six years, we have seen the quality of finished gemstones improve dramatically, and the techniques for utilizing fire agate have expanded. Kaufmann is probably the first to use fire agate in intarsia inlay on a commercial scale. Talented cutters like Joe Intili, Phil Rothengatter, Lynn Quayle, Howard Imboden, Gene Columbo, Dane Heller, Richie Sansom, and Steve Marshall, all of Arizona, have become proficient at capturing the three-dimensional appearance of fire agate and sculpting incredible works of art. The contrast of the different color layers, cut at various levels, often lends itself to unique designs that can be duplicated with no other gemstone. On rare occasions, fire agate can even be faceted. Top-quality gems sometimes sell for hundreds of dollars per carat. Despite the fact that this gemstone may never become a mass-merchandised item, it has created a small but devoted following among those who appreciate its unusual beauty.
  
  

Containing the Fire
  
  

Fire agate presents the lapidary with unusual challenges. From the rough, you can't tell if it has fire in it. Few people buy rough because it's such a gamble. We may cut 100 stones a year and end up with only a handful of good finished stones. And we have found that by the time you find a piece of rough that has good fire and is worth cutting, there's a good chance you're going to ruin it.

So before touching a rough piece of fire agate to the saw or grinding wheel, you should take time to examine it very closely. Usually the color within the rough is not visible unless the piece is chipped or broken, or if the fire layers are right on the surface. Occasionally, the color layers are visible through the chalcedony cap.

Inspect the rough stone under a bright light (sunlight is best) while the piece is wet. Magnification also helps. This will help you see where and in what direction the fire layers are oriented. The first cutting step is critical. The chalcedony cap should be removed by sawing or grinding, without going through the fire layers. There is a tendency to saw or grind right into the fire layers. Even experienced cutters ruin stones this way. The use of a thinner saw blade is one way to avoid making this mistake; when using a coarse grinding wheel, check the stone frequently.

Diamond abrasives are best. Chalcedony is a very hard material and usually a good amount of sawing and grinding is required. Once the top of the fire layers is exposed, the use of a flexible shaft is preferred. However, if the fire formation is domed or flat and the cabochon is a simple shape, it can be worked on a conventional flat grinding wheel. When using a flexible shaft, the stone can be worked in a bowl of water under a bright light. Use 100 and 400 grit sintered diamond tips (bullet or cone-shaped) for getting into the nooks and crannies.

Once the color layers are exposed, it is important to follow the contour of these layers. There are usually multiple fire layers so there is some room for error, but it is best not to take the chance of losing one layer for a less spectacular one, or running out of layers. If, however, the cutter can see brighter color layers underneath, it is usually to his or her advantage to grind more. Knowing just when to stop is something that is learned through experience.

After the initial steps are completed and the gem has been roughly ground and shaped to expose the best color, the bottom of the cabochon can be flattened. The final steps will be to bring the gemstone to a polish. If the stone is flat or domed without convolutions, it can be polished on a flat lap using tin or cerium oxide. Some cutters use a tumbler for all or part of the finishing process, but if the stone is convoluted, the tumbler tends to grind (or polish) the high spots and not get into the concave areas as well. Most serious cutters use a flexible shaft to complete the polishing process, especially on the better stones. Increasingly finer diamond tips, and nylon brushes using diamond compound. Some cutters prefer wooden or leather tips of their own creation.

Generally, the fire layers are brightest at the point of deposition, which is usually in the center of the formation. Some cutters, in order to create a larger stone, include areas that have no fire, but by removing excessive folding, brown areas, or dull fire that will detract from the overall beauty of the finished gem, you may increase the value even though the size of the gem decreases. -JW & MJG
  

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Fire Agate International

P.O. Box 32140
Tucson, Arizona  85751