Prehnite

Whilst researching Prehnite I was struck by its luminous lime green colour. Prehnite derives its name from Colonel von Prehnite, who discovered this gemstone in South Africa in 1788. Its luminous quality and lustre is only discovered once polished. It appears in yellow to mint green, pale yellow to light brown, bright yellow, grey, white and colourless. Transparent crystals are rare and usually quite small which are mainly bought by collectors. A fine green translucent prehnite has been named Cape emerald.

The majority of prehnite on the market occurs naturally as a translucent mass formed as a crust or a nodule. Yellow fibrous materials is also found and displays catoyancy (a cats eye-effect) when cut as a cabochon. It is very rare to find one as pleochroic (gemstone that appears to have several colours when viewed at different angles) if a gemstone is found to have this it increases the value. This gemstone can be translucent and clean, whereas others can be full of flaws and inclusions. Fractures with black tourmaline acicular (needle) and bright copper specks can be seen in some Prehnite.

Facetted stones are still viewed as collectable pieces and until they become commercial available there will be no set price. Cabochon and bead forms are inexpensive and readily available.

When designing with this gemstone in mind you must be aware that protection around the girdle is needed. So all around settings is beneficial as the uneven fracture makes it slightly brittle. If it comes into contact with hydrochloric acid it will become a jelly-like substance. Prehnite is regarded as a good carving material, it is soft enough to work with but still reasonable to withstand wear and tear.