Prehnite

Prehnite is an often oily green stone. It may also range from pale yellowish to brown. Columnar or tabular crystals are rare. Prehnite occurs more usually as aggregates of barrel-shaped crystals or botryoidal masses. Some pale yellowish brown prehnite if fibrous enough to be cut en cabochon. As a result, it may show the cat’s eye effect.

A prehnite stone is usually translucent. The name prehnite comes from Colonel von Prehn, who first introduced the stone to Europe.

Occurrence

Prehnite occurs in basaltic volcanic rocks and metamorphic rocks. Pale green masses are found in Scotland. On the other hand, dark green or greenish brown masses occur in Australia. Finally, aggregates of crystals are found in France.

Prehnite Properties

• Specific Gravity: 2.87
• Refractive Index: 1.61-1.64
• Birefringence (DR): 0.016
• Luster: Vitreous
• Crystal Structure: Orthorhombic
• Composition: Calcium aluminum hydroxysilicate
• Hardness: 6

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