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MINERAL OF THE MONTH

Fall 2009 – Fairburn Agate

Fairburn Agate
Fairburn Agate

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

June 2012: Moqui Marbles

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

March 2010: Fossilized Dinosaur Bone

April/May: 2010 Kentucky Agate

June 2010: Nantan Meteorite

July 2010: Mookaite Jasper

Aug/Sept 2010: Polyhedroid Agate

Fall 2010: Ammonite Fossil

Winter 2011: Argentina Condor Agate

Spring 2011: Petrfied Wood

September 2011: Petoskey Stones

January 2012: Mary Ellen Jasper

March 2012: Mexican Crazy Lace Agate

September 2012: Chlorastrolite Greenstone

March 2013: Jacobsville Sandstone

August 2013: Unakite

November 2013: Skip-an-Atom Agate

April 2014: Tiger's Eye

September 2014: Black Corundum

February 2015: Condor Agate

June 2015: Petoskey Stone

November 2015: Slag

June 2016: Lake Superior Copper Replacement Agates

August 2016: Puddingstone


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Gitche Gumee Museum.
E21739 Brazel Street
Grand Marais, Michigan 49839

 


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