prehnite

[prey-nahyt, pren-ahyt]
noun
a mineral, hydrous calcium aluminum silicate, Ca 2 Al 2 Si 3 O 1 0 (OH) 2 , occurring in light-green reniform aggregates or tabular crystals.

Origin:
1785–95; named after Col. Van Prehn, 18th-century Dutchman who brought it from South Africa to Europe; see -ite1

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Based on the Random House Dictionary, © Random House, Inc. 2014.
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prehnite

pale green to gray, glassy silicate mineral that commonly lines cavities in igneous rocks. It also occurs as stalactite masses. Prehnite is a secondary or hydrothermal mineral that is a basic calcium and aluminum silicate, Ca2Al2Si3O10(OH)2, and is often associated with zeolites. Prehnite has been found in Italy, Germany, France, Scotland, and New Jersey in the United States. Clear specimens of fine colour are sometimes cut for gem use and marketed under the name Cape emerald. For detailed physical properties, see silicate mineral (table)

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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Example sentences
Prehnite is usually a translucent light green, but can be grey, white or colorless.
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