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November 2008: Prehnite

Prehnite with copper

This yellow green mineral is found throughout the world, but most notably in Australia, South Africa, Germany, and the United States. The specimen featured this month was found in the Keeweenaw Peninsula in Michigan’s Upper Peninsula. It not only includes crystals of Prehnite, but also specs of copper, calcite, and silver. It forms near the surface of basaltic lava flows and often occurs in geodes or veins. It forms as a result of low grade metamorphism from hydrothermal solutions.

Prehnite can be confused with gyrolite, smithsonite, and hemimorphite. It can be distinguished because it is harder than these other three minerals. Smithsonite has more of a vitreous or pearly luster and hemimorphite is usually bluer in color while gyrolite is not as glassy.

Prehnite is a phyllosilicate of calcium and aluminium with the formula: Ca2Al(AlSi3O10)(OH)2. It is brittle with an uneven fracture and a slight vitreous luster with a white streak. It has a hardness of 6 to 6.5, with an average specific gravity of 2.80-2.90. It is translucent wth a color that varies from light green to grey, yellow, or white. When heated, this mineral gives up water but will not take the water back up when cooled.

Phrenite was first discovered in South Africa by Colonel Hendrik Von Prehn, an early Dutch governor of the Cape of Good Hope colony. It was the first mineral to be named after a person.

Its metaphysical properties are thought to enhance energy, provide protection, and promote calmness. It is also used to advance the state of meditation and help you to remember your dreams.

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


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