Description
The mineral prehnite is a calcium-aluminum silicate with the chemical formula Ca2Al2Si3O10(OH). The mineral belongs to the phyllosilicate family. Transparent to translucent, colorless, white, gray, or yellow to yellow-green prehnite has a vitreous to pearlescent luster, a white streak color, and distinct cleavage along the [001] crystal plane. Prehnite has an average density of 2.87 and a hardness of 6 to 6.5. The crystal system is orthorhombic, and the mineral is not radioactive. The mineral is named after the Dutch Colonel Hendrik Von Prehn (1733–1785), who discovered it in South Africa. Prehnite was the first mineral to be named after a person. Prehnite is a mineral that occurs quite commonly in hydrothermally weathered rocks. Although not a zeolite, it is often found near zeolites. It is found in granites, syenites, and gneisses, among other places. It is also an indicative mineral for the low-grade metamorphic facies prehnite-pumpellyite. The type locality is Haslach, Harzburg, and Oberstein, Germany.
