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MINERAL OF THE MONTH

April 2008: Shadow Agate

Axel's Shadow Agate

The mineral of the month is my favorite agate: the shadow agate. This specimen was picked up off the Grand Marais beach by the museum founder, Axel Niemi. He found it in 1925 when he was just eight years old. He had it for almost 40 years when he finally sliced the agate, discovering the intricate banding. The best shadow agates in the world come from Lake Superior, Botswana Africa, and Queensland Australia.

Shadow agates exhibit an optical effect of movement across the bands. Depth is perceived from light penetrating and bouncing between alternating clear and opaque layers. When you move these agates back and forth, shadows can be seen racing across the surface. Many factors contribute to the shadow phenomenon including the regularity, contrast, distance, and depth of the bands. When the right conditions exist, light disappears into the clear chalcedony bands and is not reflected back out to the eye. When little or no light is returned to the line of sight, we interpret this as a dark region, or shadow.



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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