Prehnite

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Prehnite is a phyllosilicate of calcium and aluminium with the formula: Ca₂Al(AlSi₃O₁₀)(OH)₂. Limited Fe³⁺ 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 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 basaltic rocks, sometimes in granites, syenites, or gneisses. It is an indicator mineral of the prehnite-pumpellyite metamorphic facies. It was first discovered in South Africa by Colonel Hendrik Von Prehn, an early Dutch governor of the Cape of Good Hope colony. Prehnite was the first mineral to be named after a person.

1 Gallery
2 See also
3 References
4 External links

[edit] Gallery

Round cut Prehnite, 1.7 cm diameter x 1.3 cm high, 3.2 grams.	Emerald cut Prehnite, 1.85 cm x 1.42 cm, 4.6 grams.	Prehnite cabochon, 2.6 cm x 1.54 cm, 5.1 grams.	Prehnite, carved pendant, 2.0 cm x 1.3 cm, 4.0 grams.
Carved yellow Prehnite pendant, 2.4 cm x 1.8 cm, 5.5 grams.	Botryoidal Prehnite fragment, 12.0cm x 11.0cm, 646 grams.	Prehnite nodule fragment, 11.0cm x 7.0cm, 338 grams.	Prehnite nodule showing cleavage planes where it has separated from a cluster, 5.5cm diameter, 134 grams.
Prehnite nodule, 5.0cm diameter, 82 grams.	Sliced Prehnite fragment with calcite core, 9.0 cm diameter.	Prehnite, New Haven Co. CT, USA	Prehnite, Franklin, New Jersey, USA
Prehnite, Epidote