Prehnite Tumbled Stone

Prehnite is a calcium aluminium silicate - Ca₂Al₂Si₃O₁₀(OH)₂ - in the soft green-to-gold range, Mohs 6–6.5. It grows in the gas cavities of volcanic basalt, often in rounded, grape-like crusts, alongside zeolite minerals.

Its character is translucency: light passes a little way into the stone and scatters, giving the clouded, lit-from-within look often compared to sea glass. The colour is usually a pale celadon, sometimes warming toward yellow-green.

Fine prehnite carries faint internal fibres - sometimes needles of black epidote - which the trade reads as a mark of the natural stone rather than a flaw.

Asked often

Why does it look cloudy or lit from within?
Prehnite is translucent - light enters and scatters inside the stone. That soft glow, like sea glass, is the natural character, not a polish fault.

Is the colour natural?
Yes. The pale green-to-gold is the mineral’s own; fine pieces are untreated. Faint internal needles are natural and a sign of the genuine stone.

Is the name really from a person?
Yes - it was named in 1788 after Colonel Hendrik von Prehn, who brought the first specimens from the Cape to Europe. It was the first mineral named after a person, a convention that became standard after it.

How do I look after them?
Wipe with a soft cloth. At Mohs 6–6.5, a little softer than quartz - spare them hard knocks.

1. Carried in a pocket or a bag, or held in the hand.
2. Kept in a small dish, on a desk, or on a shelf - each stone is a little different.
3. Wipe with a soft cloth; a little softer than quartz, so spare them hard knocks.

Each stone is tumble-polished and unique, so a set varies a little stone to stone. Many keep a stone where they will see it each day, or carry one in a pocket; that is a matter of preference.

Pocket stones to keep and carry. Wipe with a soft cloth; a little softer than quartz, so spare them hard knocks.

• Stone: Prehnite · calcium aluminium silicate
• Hardness: Mohs 6–6.5
• Character: Translucent · pale celadon to yellow-green
• Treatment: None · untreated
• Form: Tumbled stones · polished, each unique · sold in a set
• Origin: Mali
• Care: Wipe with a soft cloth · spare hard knocks

Prehnite holds a small place in the history of science: described in 1788, it was the first mineral ever to be named after a person - Colonel Hendrik von Prehn, who carried the first specimens from the Cape of Good Hope to Europe. Every mineral since named for a discoverer follows the precedent this stone set.

Before that naming it was simply a translucent green stone collectors prized for its glow; it has been cut and worn wherever it was found. What people have read into that inner light is theirs, and now yours.