MINERAL OF THE MONTH
August and September 2010 - Polyhedroid Agate
The mineral of the month for August/September is the Polyhedroid Agate. The unique polyhedroids are strange looking agates with geometric shapes that have smooth flat sides. Their shape appears more angular than the typical almond-shaped agate, but there is no consistency to the angles of formation. Most are either triangular or trapezoid and hollow, with the bands running parallel to their shape. Although no one knows for sure how these agates formed, there are at least two theories. Some believe that polyhedroid agates are pseudomorph replacements of other, more angular crystals. Another hypothesis is that they formed in spaces between other crystals, perhaps calcite. Unlike the rest of the Brazilian agates found in the southern part of the country, these unusual agates are found at a single site in the northern state of Paraiba. There has been no mining of polyhedroids in recent years. Most were mined during the 1970s. Believe it or not, a few polyhedroids have also been found in the Lake Superior region and in Wyoming.
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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
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
September 2011: Petoskey Stones
Spring 2011: Petrfied Wood
Winter 2011: Argentina Condor Agate
January 2012: Mary Ellen Jasper
March 2012: Mexican Crazy Lace Agate
June 2012: Moqui Marbles
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
March 2017: Chert
July 2017: Kona Dolomite
December 2017: Septarian Nodule
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