Prehnite Gemstone Beads from Rings & Things: Prehnite beads are also known as cape emerald beads and look extremely similar to green tourmalated quartz beads. Usually ranging from pale to grass green, prehnite can also be gray, white, black, brown or colorless. These semiprecious beads are hard, durable gemstones consisting of a hydrous silicate of alumina and lime. Their bright, almost luminescent coloring frequently features inclusions of black amphabole, which make them easy to confuse with green tourmalated quartz. Prehnite's luster is vitreous to waxy, and its crystals are transparent to mostly translucent. This gemstone is often found with zeolites, but the two stones are from different geologic classes. Other minerals confused with prehnite include gyrolite, smithsonite, and hemimorphite. Known as the "prediction stone", prehnite is believed to enhance dreaming and remembrance. Crystal healers use it to reduce high blood pressure and control hypertension.