MINERAL OF THE MONTH
April 2008
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 Mineral of the Month
June 2007 Mineral of the Month
July 2007 Mineral of the Month
August 2007 Mineral of the Month
Fall 2007 Mineral of the Month
December 2007 Mineral of the Month
January 2008 Mineral of the Month
February 2008 Mineral of the Month
March 2008 Mineral of the Month
April 2008 Mineral of the Month
May 2008 Mineral of the Month
June 2008 Mineral of the Month
Summer 2008 Mineral of the Month
September 2008 Mineral of the Month
Copyright All rights reserved.
Gitche Gumee Museum.
E21739 Brazel Street
Grand Marais, Michigan 49839
