Prehnite is an inosilicate of calcium and aluminium with the formula: Ca<sub>2</sub>Al(AlSi<sub>3</sub>O<sub>10</sub>)(OH)<sub>2</sub> with limited Fe<sup>3+</sup> substitutes for aluminium in the structure. Prehnite crystallizes in the orthorhombic crystal system, with only just the crests of small crystals showing any faces, which are almost always curved or composite. Very rarely will it form distinct, well-individualized crystals showing a square-like cross-section, including those found at the Jeffrey Mine in Asbestos, Quebec, Canada. Prehnite is brittle with an uneven fracture and a vitreous to pearly luster. Its hardness is 6.5, its specific gravity is 2.80–2.95 and its color varies from light green to yellow, but also colorless,
Extensive deposits of gem-quality prehnite occur in the basalt tableland surrounding Wave Hill Station in the central Northern Territory, of Australia.
Gallery
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Image:prehnite-pf-0002.jpg|Emerald cut prehnite, 1.85 cm × 1.42 cm, 4.6 grams.
Image:Calcite-Prehnite-188139.jpg|Thin plate of pea-green prehnite on which have grown calcites
Image:Prehnite-273380.jpg|Water green color spheres of crystallized prehnite with minor calcite on basalt
Image:prehnite-pp-0134.jpg|Carved yellow prehnite pendant, 2.4 cm × 1.8 cm, 5.5 grams
Image:Prehnite-288989.jpg|Pastel-green rosettes of prehnite blades on matrix
Image:prehnite-ps-0107-DV00018.jpg|Prehnite nodule fragment, 11.0 cm × 7.0 cm, 338 grams.
Image:prehnite-ps-0128.jpg|Sliced prehnite fragment with calcite core, 9.0 cm diameter.
Image:Prehnite-131722.jpg|A 2 cm prehnite ball of top quality and color
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See also
- List of minerals
- List of minerals named after people