Also found in: Dictionary, Wikipedia.


Ca2 Al2Si3O10(OH)2 A light-green to white mineral sorosilicate crystallizing in the orthorhombic system and generally found in reniform and stalactitic aggregates with crystalline surface; it has a vitreous luster, hardness is 6-6.5 on Mohs scale, and specific gravity is 2.8-2.9.



(named after the Dutch colonel Prehn, who discovered the mineral on the Cape of Good Hope), a sorosilicate mineral that has the chemical composition Ca2 Al[AlSi3O10]·(OH)2 with a trace of Fe replacing the Al. Prehnite crystallizes in the rhombic system. Clearly formed crystals usually have a prismatic, tabular habit and are rare. Prehnite is mainly found as nodular aggregates with radial-columnar structures. It is greenish yellow or gray. Its hardness on Mohs’ scale is 6.5 and its density is 2,800–2,950 kg/m3.

Prehnite is an ordinary hydrothermal mineral that occurs in the cavities of basic effusive rocks together with such minerals as zeolites, calcite, and epidote. It also forms in metamorphic rocks, for example, skarns, and during the decomposition of plagioclases in gabbro and diabases.

References in periodicals archive ?
La chlorite, la prehnite et la pumpellyite mineralisee de facon eparse presentes, indiquent que les roches ont atteint le stade d'un facies a prehnite-actinolite.
Some calcic mafic rocks may contain prehnite instead of chlorite.
3), which defines the upper boundary of the prehnite-pumpellyite subfacies, as most mafic rocks do not contain prehnite and pumpellyite in this P-T range.
Most samples contain relict igneous minerals, variably replaced by fine-grained metamorphic minerals dominated by chlorite, epidote, actinolite, prehnite, pumpellyite, quartz, and opaque minerals.
Iron in epidote and prehnite substitutes for Al and hence is assumed to be ferric.
Most prehnite analyses, with the exception of sample 4, show good agreement with the ideal formula, ([Ca.
The simplest explanation for the compositional lamellae, which are too fine to be seen optically, is two phases of growth of prehnite via two different reactions, as discussed later in this paper.
Correlation between prehnite composition and grade is not apparent in our data.
As with prehnite noted above, compositional variation occurs on the [micro]m scale.
10, Table 3) involves the ultimate breakdown of pumpellyite to chlorite, prehnite and epidote.
Figure 11d shows chlorite-pumpellyite pairs in most of the same samples as projected from prehnite (sample 2 does not contain prehnite and is omitted).
Sample 8 does not contain prehnite and is therefore not included in Fig.