MINERAL OF THE MONTH
Fall 2009 – Fairburn Agate
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The Fairburn Agate is the state stone in South Dakota. It is named after the town from which the first agates were found: Fairburn, SD. This is an unusual agate, in that they formed in sedimentary rock, rather than igneous rock in which most other agates formed. This sedimentary genesis probably contributed the minerals which cause the brilliant color of Fairburns. These agates are also known for the extreme color contrast in the banding. The agate bands typically have sharp peaks, often resembling a maple leaf pattern. Most Fairburns have concentric fortification banding.
These agates are found in the grassland and badland areas surrounding the Black Hills, located in the southern part of the state. It is believed that the sedimentary rock matrix in which the agates formed were uplifted when the Black Hills formed. As the limestone eroded, the hard agates eroded out. As they moved downstream with eroded material, many of the Fairburns were rounded and river polished.
The value of a Fairburn agate is determined by size (most are small—only a few ounces), color, quality of banding, number of bands, shape of the fortification pattern, and condition (fracture free). As far as I know, a Fairburn agate still has the record for the highest priced agate sold on EBay. Several years ago, a Fairburn agate sold for $13,000.
Mineral of the Month Archives
May 2007 Rainbow Fluorite
June 2007 Lake Superior Michipicoten Agate
July 2007 Labadorite
August 2007 Rain Flower Agate
Fall 2007 Malachite
December 2007 Nepheline Syenite
January 2008 Native Copper
February 2008 Amazonite
March 2008 Lake Superior Agate
April 2008 Shadow Agate
May 2008 Apohpylite
June 2008 Ocean Jasper
Summer 2008 Marra Mamba Tiger's Eye
September 2008 Mohawkite
October 2008 Mexican opal
November 2008 Prehnite
December 2008 Picture Jasper
January 2009 Sea Shell Jasper
February 2009 Polychrome Jasper
March 2009 Selenite Desert Rose
Spring 2009 Coyamito Agate
July 2009 Obsidian Needles
August 2009 Goethite
September 2009 Banded Iron Formation
Fall 2009 Fairburn Agate
February 2010 Kentucky Agate
March 2010 Fossilized Dinosaur Bone
April/May 2010 Kentucky Agate
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