Prehnite

Prehnite properties at a glance

Geology & background

Prehnite forms as a secondary mineral lining cavities and fractures in volcanic rocks, and also in metamorphosed rocks, where calcium-rich fluids crystallize at low temperatures.

Prehnite was described in the late eighteenth century from material collected at the Cape of Good Hope and is often cited as the first mineral named after the person who discovered it.

How to identify Prehnite

• Look for soft green to yellow-green color and rounded, botryoidal aggregates lining rock cavities.
• Prehnite is moderately hard, translucent, and has a glassy luster on crystal surfaces.
• It commonly occurs in basalt with zeolites, calcite, and epidote, which helps confirm identification.

Where Prehnite is found

Prehnite occurs in volcanic cavities and metamorphic rocks worldwide, with notable specimen localities in South Africa, Australia, China, the United States, Scotland, and France.

How much is Prehnite worth?

Value depends on color, translucency, crystal form, size, locality, matrix, and overall condition.

Common uses

• Cabochons and gemstones
• Jewelry
• Lapidary carving
• Ornamental objects
• Collector specimens

Interesting facts

• Prehnite was one of the first minerals to be named after a person, the Dutch officer Hendrik von Prehn.
• It often grows as rounded, grape-like botryoidal masses built from tightly packed crystals.
• Translucent green prehnite can show a soft internal glow that lapidaries cut into cabochons.
• Needles of epidote or other minerals are sometimes trapped inside prehnite, creating striking specimens.

Care & safety

Prehnite is moderately hard and fairly tough, but sharp impacts can chip botryoidal surfaces.

Avoid inhaling dust. Do not cut, grind, or polish unknown specimens without eye protection and a proper respirator.

Related rocks & minerals

Calcite Minerals Quartz Quartz Family Epidote Minerals Datolite Minerals Apophyllite Minerals Jadeite Silicate Minerals