925/000 Silver earrings with Prehnite from Mali

The mineral prehnite is a calcium aluminum silicate with the chemical formula Ca2Al2Si3O10 (OH). The mineral belongs to the phyllosilicates. The transparent to translucent colorless, white, gray or yellow to yellow-green prehnite has a glass to pearlescent luster, a white stripe color and the cleavage is clear according to the crystal plane. Prehnite has an average density of 2.87 and the hardness is 6 to 6.5. The crystal system is orthorhombic and the mineral is not radioactive. The mineral prehnite is named after the Dutch colonel Hendrik Von Prehn (1733 - 1785), who discovered the mineral in South Africa. Prehnite was the first mineral to be named after a person. Prehnite is a mineral that is quite common in hydrothermally weathered rocks. Although not a zeolite, it is often found near zeolites. It is found in granite, syenite and gneisen, among others. It is also an indicative mineral for the low-grade metamorphic facies prehnite-pumpellyite. The type location is Haslach, Harzburg and Oberstein, Germany.