Prehnite from Patterson, New Jersey
Prehnite from Bendoukou, Sandare
District
Prehnite on Epidote
CHEMISTRY - Ca2Al2Si3O10 (OH)2
CRYSTALLOGRAPHY - Orthorhombic
CRYSTAL GROWTH AND HABITS - Crystals are tabular (parallel to {001}) or prismatic or steeply pyramidal. However, crystals are uncommon and Prehnite typically forms aggregates that are globular, reniform or stalactitic. It can also be granular or compact massive.
COLOR AND OPTICAL PROPERTIES - Most commonly it is light to dark green but it can also be white, yellow, and shades of pink or gray. It is typically translucent.
HARDNESS - 6 - 6.5
SPECIFIC GRAVITY - 2.80 - 2.95
LUSTER - Commonly vitreous to slightly pearly along {001}.
STREAK - White
BREAKABILITY - Prehnite has good cleavage along {001} and poor cleavage along {110}. It also has an uneven fracture.
OCCURRENCE - Prehnite is a secondary mineral (or hydrothermal) found along veins in mafic igneous rocks like basalt. It is less common felsic rocks.
ASSOCIATED MINERALS - It is commonly found with Zeolites, Calcite, Datolite, Pectolite, Epidote and even Copper.
MINERAL NAME - It is named after its discoverer, Colonel Hendrik von Prehn.