MINERAL OF THE MONTH
November 2008: Prehnite
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.
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