PREHNITE

HISTORY, NAME, LOCALITIES: Prehnite, discovered in South Africa by Dutch colonial governor Colonel Hendrik von Prehn Africa in 1777, was recognized as a mineral species in 1789 and named for von Prehn.  Collecting localities are found in South Africa, Morocco, Switzerland, Mali, Australia, India, Canada, and the United States (New Jersey, Virginia, Michigan, Washington).

MINERALOGY, PROPERTIES, OCCURRENCE: Prehnite [basic calcium aluminum silicate, Ca₂Al₂Si₃O₁₀(OH)₂], pronounced PRENN-ite, crystallizes in the orthorhombic system as pale-to-dark-green, botryoidal masses with distinctively ridged surfaces, and rarely as short, tabular or prismatic crystals.  An uncommon but widely distributed phyllosilicate mineral, prehnite has a Mohs hardness of 6.0-6.5, good cleavage in one direction, vitreous-to-waxy luster, and a specific gravity of 2.8-2.9.  As a secondary mineral, prehnite forms in vugs in basaltic rocks through hydrothermal metamorphism and is often associated with zeolite minerals.

METAPHYSICAL PROPERTIES, LORE, USES:  According to modern metaphysical practitioners, prehnite guards against unsettling and disruptive forces, enhances meditation, and is a “dream stone” that encourages lucid and memorable dreams.  Prehnite is the first mineral discovered that has a South African type locality.  Prehnite, a minor gemstone known as “Cape emerald,” is fashioned into cabochons for use in jewelry.  It has no technological uses.

COLLECTORS’ INFORMATION: Mineral collectors value individual specimens of prehnite for their subtle colors, unusual ridged surfaces, and pleasing luster.  Composite specimens with zeolite minerals offer attractive color contrasts.