What is a Fairburn Agate
Fairburn agate is a particular type of fortification agate, often brightly-colored, first found near the village of Fairburn, Custer County, South Dakota. It has been designated as the official state gemstone for South Dakota. The agates are characterized by sharp "holly leaf" banding, somewhat resembling an aerial view of an old fort, hence the name fortification agate. What differentiates them from most other agates found world-wide is the very large range of colors in the agate itself. In addition, the bands can be very intricate and thin, ranging up to very wide (the wide bands are comprised of very thin bands all the same color). Sometimes the color in an individual band can result from a blending of a background color with contrasting color dots or tiny blobs. (e.g., red dots on a white band to give a pink appearance) And sometimes the color of an individual band itself can vary from place to place in the agate nodule.
Fairburns are similar in appearance to many Mexican agates, but have a tendency to less transparency, especially in the matrix or non-banded part of the nodule, which is usually very jaspery. They are also similar to Tepee Canyon, Custer State Park agate, and also Dryhead, Montana agates, with the exception that Fairburns and State Park agates do not show color tendencies nearly as sharply. For instance, a traditional Tepee Canyon agate will run in red-orange to orange in the outside bands, through yellow to white on the inside, often with colorless quartz or calcite directly in the center. However, expert collectors can frequently guess where a particular Fairburn was collected by certain color tendencies. For example, agates from the Oelrichs, South Dakota area often tend to black and white, or dull red and gold banding. Agates from the Nebraska and the nearby Ardmore, South Dakota beds are frequently larger and have more matrix area than their South Dakota counterparts. Black, Brown, and whites or creams, tans, beige or orange bandings are very common from there. Bright reds also come from Nebraska as well as Lame Johnny Creek in South Dakota. Pink and black and white are often seen from Scenic or Creston, South Dakota. The original area (the Kern Beds) east of Fairburn is famous for pinks, corals, salmons, bright oranges, deep reds to violet and yellows. Brick-red, medium grayish, or tan seems to be common matrix colors there. Caramel and white coloration is very common from the Sioux reservation areas. Agates from the Oral, South Dakota gravel pit are often very similar to Tepee Canyon. It is beyond the scope of this page to cover all of the tendencies, plus we are still learning.
For a full discussion, read the chapters in Roger Clark's new book, Fairburn Agate, Gem of South Dakota. Some collectors, including Roger, are still skeptical about supposed color and other identifying tendencies. Others, like Wayne Shortridge, are much more convinced. This is covered in Roger's excellent book, and is explained in much more detail there.
Location of Fairburn Agates
Some scientists have speculated that these agates were deposited along with the other myriad of jaspers, jasp-agates, "prairie agates", petrified wood, quartz nodules and other nodules by glaciers or alluvium coming down from the nearby Black Hills. Rounded cobbles of rose quartz and black tourmaline are occasionally found in the agate beds, indicating their source from the nearby pegmatites there. Roger Clark presents evidence for this theory in his first book on Fairburns, South Dakota's Fairburn Agate, now out of print. In fact, he shows pictures of agates collected in situ in the Black Hills themselves which are nearly identical to those collected in the badlands and prairies. This theory would place State Park agates and Tepee Canyon agates as merely varieties of Fairburns, in the sense that they all originated in the Minnelusa limestone formation here. The Dryhead agate of Montana is found in the Embar Formation, which is likely a contemporary formation, but formed further west.
The old theory was that the agates and jaspers themselves were formed very close to the place they are now found. Some localities, e.g. Glendo, Wyoming, often show a rough exterior, indicating that the agate nodule has not traveled too far in an alluvium mix. They are mostly associated with the Chadron sedimentary clay formations. However, a study of detailed geologic maps or field studies may show that the Minnelusa does (or did) outcrop other places (other than the So. Dakota Black Hills), and the agates could have easily eroded out and been captured in sediments of the White River Group (the Chadron is a part of those formations) during past geological times.
Fairburn agates occasionally contain fossils or fossil imprints, as do the common jaspers and jasp-agates they occur with. These fossils are often small marine shells, but I do have several samples of crinoid sections imbedded within the nodules. This would place the origin of the nodules somewhere around the Pennsylvanian age. There is still much study and debate taking place regarding the formation of agates. They are attributed to percolating solutions of hot silica containing various amounts of chemical impurities (the impurities give the colors of the matrix and bands). These agates (as are the Dryhead agates of Montana and the Keswick and "coldwater" agates of Iowa, the Union Road agates of Missouri, and the banded agates of Kentucky and Tennessee are all formed in sedimentary formations, unlike many of the world's agates, which were formed in igneous rocks. Chert and flint, along with myriads of jasper nodules are also found in sections of sedimentary rocks. These are all similar in composition to agate. The cavities these nodules formed in were evidently marine in nature.
The primary area where Fairburns are found is in a wide band just outside the Black Hills to the east and south, extending from a point east of Rapid City through the Badlands National Monument, and along the White River and Cheyenne River breaks into the northwest tip of Nebraska (north of Crawford), and extending a few miles east into Wyoming. Part of the area in South Dakota includes the Pine Ridge Indian Reservation. Collecting is prohibited in the National Monument, and strongly advised against on the reservation unless you are native Lakota Sioux. Some native collectors often sell their finds to the local rock shops, or sell directly at shows. Frequently agates are reported in old gravel pits near Creston and Oral, South Dakota, and also apparently in times past near Rushville and Gordon, Nebraska. It was thought for a long time that there are none on the west or north sides of the Black Hills, but Wayne Shortridge of Ft. Collins found a Fairburn-type agate in place in a limestone formation near Newcastle, Wyoming. Roger Clark's book has maps showing several agate collecting localities in the Black Hills, including Antelope Springs, S&G Canyon, Pringle, and Dow Ridge. I don't know what the collecting status is at any of these locales. Some may be on private land. To the southwest are the Glendo, the Guernsey, Lance Creek, and the Hat Creek areas in Wyoming. Fairburn type agates have also been found occasionally far to the south near New Raymer, Colorado (north of Ft. Morgan). A study of geological maps show scattered outcrops of the Chadron Formation in that area. I have hunted this area very briefly (last time in 2004) with no success, but the other agate/jasper materials found there are very similar to those found in the other badlands areas. I also have one large sample found near the Yampa River in northwest Colorado (see picture gallery), but have not personally hunted there yet.
Roger Clark reports of a find by a collector from the Belle Fourche River just north of the Black Hills. And collector Larry Field of Montana brought some samples, some of which appeared to be Fairburn-type agate collected in the Yellowstone River in Montana, northwest of the Black Hills, to the Crawford swap in 2003. Most of these tend to be somewhat dull in color, with browns, grays, dull yellows, etc. predominating, but I have seen pictures of some brighter ones.
Since these often beautiful and intriguing agates have always been very scarce (and hence expensive to purchase) it might be good to search for new localities. Common Fairburns run $5 to $50, while really nice ones can go for up to $500 or more. Museum quality can often fetch more than $1,000. The record so far is over $13,000 for a single agate! Prices are continuing to climb, with more interest in the Fairburn producing more competition for them. It's the old "supply and demand" routine.
The agates, which can be whole nodules or broken pieces, range from the size of a pea to the size of a cantaloupe (extremely rare!) or larger. An average one is maybe one to two inches across (maybe larger for the Nebraska type). Prices may seem high (or even insane) to the casual collector until you have spent hours wandering around the agate beds in a stooped-over position in the hot sun trying to find one. Bring lots of liniment and suntan lotion and watch for prickly pear cactus and rattlesnakes! The old original Kern Beds east of Fairburn are over-hunted at this point, although new agates weather out and excellent finds are made every year by the persistent (see the picture at the bottom of a super agate over 3" across found laying right out in the open by friend Wayne Shortridge in May, 1996! The color is nicer than the photo shows.)
How to Display Fairburn Agates
Fairburns are seldom made into jewelry due to their scarcity. The preferred display method is to leave the finest ones unpolished, or "faced off" only (if need be), while average to lower quality ones can often be polished whole by sanding or tumbling methods. Sanding offers much more control and is usually much more satisfactory, although a combination of the two methods work well. Fairburns which have a water-worn and natural patina are usually left alone, but some of the ones that haven't weathered very far from their origin (such as some of the Wyoming agates) are often rough and sometimes show ugly limey coatings and can often be improved by lapidary, acid cleaning, or air abrasive procedures.
There is a fair amount of controversy today over whether agates should be polished or left natural. I say it depends on the piece. The finest specimens are usually left unpolished, as that is the preference of many modern collectors. Good unpolished specimens also tend to fetch the highest prices.Some collectors who prefer unpolished are very adamant about their viewpoint. Personally, I look at it as something of a "lemmings" attitude, as I look at it as mostly a personal preference. We can't all afford a nice collection of unpolished full-faced agates like some of the top collectors own. Many rather ordinary or even homely agates have been greatly improved in color and pattern with lapidary procedures.
On the other hand, why bother to polish a nice agate that is already beautiful as it is and has a nice natural shine or patina from tumbling around in the badland gravels? Some agates should never be polished because the outside appearance is due to chemical changes in the outer weathered layers. This is especially true with many agates with black bands. Cutting and polishing often removes the black coloring in the bands and often the unoxidized colors are not as pleasing or as contrasting--although sometimes it brings out bright reds or pinks. True black bands can exist that go all the way through, but that is less often the case. The most desirable agates almost always show good color contrasts between the bands and/or matrix. Furthermore, the most desirable specimens tend to exhibit whole or "full-face" patterns. If the pattern wraps around the stone, it detracts some from the value. Too much matrix also detracts.
Some collectors in fact limit their collection to unpolished and/or full-faced pieces. However, the supply of really good agates fitting this description is severely limited and competition is fierce. The best source is buying old estates (if you can afford it and are at the right place at the right time), or from the small steady output available from Native Americans. Some of the Sioux collectors have their own fine family collections which are seldom for sale, but they still find enough extras to frequently sell to shops or other collectors. Of course, if you live in the area, you can always hunt your own, but it's a slow process trying to build up an impressive collection that way. Not only that, but agates from certain areas are not available by self-collecting--some areas are now closed or off-limits.
From another viewpoint, an expert lapidary can often bring out much finer or larger patterns hidden beneath the surface. Sometimes grinding will remove much or all of the banding which is only on the surface, and other times it will open it up, as much of the pattern is hidden within. Grind slowly until you can observe which is happening. If it is a fine specimen to begin with, you may wish to consult an experienced Fairburn cutter before putting it to the wheel to increase your chances of success. Sawing with a diamond blade can be done on lesser specimens as well, to find out what may be hidden within, or to remove excess matrix areas. Sawing can diminish value also, but with lesser agates, it is not an issue. I'd much rather have a nice trimmed piece than lug around a big chunk of homely jasper matrix with a small pattern at one end. As with fine crystal mineral specimens, it is considered something of a sacrilege to cut up the fine quality ones for jewelry. If crack-free however, the smaller pieces can make beautiful cabochons.
Wayne's Prize Fairburn found in 1996.
***End of My Fairburn Blog. If you have any comments or questions about this article, you are welcome to email me.***