DigMyGem Gem encyclopedia

Prehnite

Other Silicates & Gemstones

Prehnite is a calcium-aluminium silicate that commonly forms rounded botryoidal crusts or radiating masses. Gem material is usually translucent pale green to yellow-green, while transparent crystals suitable for faceting are uncommon.

Identity

Material or variety
Prehnite
Scientific or material identity
Prehnite
Classification
Natural mineral or mineral variety
Composition or formula
Ca₂Al(AlSi₃O₁₀)(OH)₂
Crystal system or structure
Orthorhombic
Geological or manufacturing origin
Can form in more than one geological environment, or combines several materials.
Mohs hardness
6 to 6.5

Origins

Australia · Canada · China · South Africa · USA

Appearance & optical properties

translucent apple-green prehnite with soft radiating texture.

History & discovery

Specimens collected in South Africa's Eastern Cape were described in the late eighteenth century. The mineral was named for Colonel Hendrik von Prehn, who brought material from the Cape to Europe, making prehnite an early mineral named after a person.

Uses & care

Common uses
Translucent prehnite is commonly cut as cabochons, beads, and carvings; rare clear crystals may be faceted, and botryoidal groups are collected as specimens.
Handling and cleaning
Use warm soapy water and a soft cloth. Prehnite is brittle and has good cleavage, so protect it from blows, pressure in a setting, steam, ultrasonic cleaners, and sudden temperature changes.

Jewellery

5 pieces of Prehnite jewellery. Learners earn each one in DigMyGem by learning words; until then it shows as a silhouette.

  • Silhouette of Cape Emerald Pendant

    Cape Emerald Pendant

    Pendant

    A translucent apple-green prehnite cabochon, the stone once mis-sold as Cape emerald, hung in a vine of gold. Its soft green is the colour of new leaves under cloud.

  • Silhouette of Grape-Cluster Brooch

    Grape-Cluster Brooch

    Brooch

    A brooch carved as a bunch of grapes from prehnite, the stone botryoidal habit shaping each grape. Tiny gold leaves and a gold stem finish the cluster.

  • Silhouette of Prehnite Cabochon Ring

    Prehnite Cabochon Ring

    Ring

    A high-domed green prehnite cabochon in a plain gold ring, cut tall because prehnite is rarely clear enough to facet. The stone is said to quiet a restless mind.

  • Silhouette of Green Grape Earrings

    Green Grape Earrings

    Earrings

    An imagined pair of drop earrings, each a translucent pale green prehnite pear hanging from a small gold vine leaf, the colour of a grape not yet ripe.

  • Silhouette of Cape Vineyard Necklace

    Cape Vineyard Necklace

    Necklace

    An imagined gold necklace of vine leaves and grape clusters of prehnite, first found near the Cape of Good Hope.

Sources