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MINERAL OF THE MONTH

Spring 2009

Coyamito Agate from Chihuahua, Mexico

The mineral of the month is the Coyamito Agate from northern Mexico. It is mined on a ranch located around 40 miles from the world famous Laguna Agate location, which is around 75 miles south of El Paso, Texas. The ranch is in the middle of the Chihuahuan desert at an elevation of just under 5,000 feet. For the past 50 or 60 years, the Coyamito has been one of the most sought after Mexican agates. They display a wide array of colors with fine banding, and the most unusual pseudomorphs of any agate on earth. Both of the specimens featured in the photos below are agates that formed when silicon dioxide replaced aragonite crystals.

When a highway was built through this desert during the 1940s, rockhounds began venturing into the area. Mineral claims were made in the late 1940s and prospectors have been searching for these valued agates ever since. By the 1960s, most of the agates were already extracted. More searching resumed in the early 1990s, when two people died while using explosives. Rockhounding on the ranch was prohibited until the last few years, when special permission was given to a few well-known agate collectors. These prospectors had to quarry directly into 38 million year old andesite, and carefully, but with much difficulty, remove the nodules from the very hard matrix.

The specimen pictured on the two left photos is a sagenite-like pseudomorphs that has botryoidal formation on the top and back. The specimen on the two right photos is a pseudomorph Coyamito agate with a drusy quartz layer on top. The appendages most likely formed when agate replaced a needle-like mineral, such as goethite. You can see in the far right picture that in cross-section, the agate bands have an eye-like stalactite formation. I purchased this specimen already cut into the three sections. I am selling this unusual group as a set. If you are interested, please send me an email to karen @ agatelady.com.

Coyamito Sagenite - Front View Coyamito Sagenite - Back ViewCoyamito AgateCoyamito Group

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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