Prehnite
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'''Prehnite''' is a [[Silicate minerals|phyllosilicate]] of [[calcium]] and [[aluminium]] with the formula: Ca<sub>2</sub>Al(AlSi<sub>3</sub>O<sub>10</sub>)(OH)<sub>2</sub>. Limited Fe<sup>3+</sup> substitutes for aluminium in the structure. Prehnite crystallizes in the [[orthorhombic]] [[crystal]] system. It is brittle with an uneven fracture and a vitreous to pearly lustre. Its [[Mohs scale of mineral hardness|hardness]] is 6-6.5, its [[specific gravity]] is 2.80-2.90 and its color varies from light green to grey or white. It is translucent.
Though not a [[zeolite]], it is found associated with them and with [[datolite]], [[calcite]], etc. in veins and cavities of [[basalt]]ic rocks, sometimes in [[granite]]s, [[syenite]]s, or [[gneiss]]es. It is an indicator mineral of the [[Prehnite-pumpellyite facies|prehnite-pumpellyite metamorphic facies]]. It was first discovered in [[South Africa]] by Colonel Hendrik Von Prehn, an early [[the Netherlands|Dutch]] governor of the [[Cape of Good Hope]] colony. Prehnite was the first mineral to be named after a person.
==Gallery==
<gallery>
Image:prehnite-pf-0001.jpg|Round cut Prehnite, 1.7 cm diameter x 1.3 cm high, 3.2 grams.
Image:prehnite-pf-0002.jpg|Emerald cut Prehnite, 1.85 cm x 1.42 cm, 4.6 grams.
Image:prehnite-pf-0003.jpg|Prehnite cabochon, 2.6 cm x 1.54 cm, 5.1 grams.
Image:prehnite-pp-0112.jpg|Prehnite, carved pendant, 2.0 cm x 1.3 cm, 4.0 grams.
Image:prehnite-pp-0134.jpg|Carved yellow Prehnite pendant, 2.4 cm x 1.8 cm, 5.5 grams.
Image:prehnite-ps-0100-DV00003.jpg|Botryoidal Prehnite fragment, 12.0cm x 11.0cm, 646 grams.
Image:prehnite-ps-0107-DV00018.jpg|Prehnite nodule fragment, 11.0cm x 7.0cm, 338 grams.
Image:prehnite-ps-0108-DV00019.jpg|Prehnite nodule showing cleavage planes where it has separated from a cluster, 5.5cm diameter, 134 grams.
Image:prehnite-ps-0116-DV00035.jpg|Prehnite nodule, 5.0cm diameter, 82 grams.
Image:prehnite-ps-0128.jpg|Sliced Prehnite fragment with calcite core, 9.0 cm diameter.
Image:Prehnite_HMNH1.jpg|Prehnite, New Haven Co. CT, USA
Image:Prehnite09.jpg|Prehnite, Franklin, New Jersey, USA
Image:Prehnite Epidpte edit.jpg|Prehnite, Epidote
</gallery>
==See also==
*[[List of minerals]]
*[[List of minerals named after people]]
==References==
*Hurlbut, Cornelius S.; Klein, Cornelis, 1985, ''Manual of Mineralogy'', 20th ed., ISBN 0-471-80580-7
==External links==
*[http://www.prehnite.com.au/specimens.html Prehnite website]
[[Category:Phyllosilicates]]
[[Category:Calcium minerals]]
[[Category:Aluminium minerals]]
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[[ru:Пренит]]