A Dutch colonel, H. Von Prehn, is credited with discovering Prehnite in 1774 at the Cape of Good Hope in Africa. Early traders nicknamed the gemstone Cape Emerald in hopes of exploiting its green color.
Prehnite was originally classified as a Zeolite, due to the fact that it usually forms in the same areas and under similar conditions as the zeolite. Today geologist place it in the phyllosilicate category which also includes apophylite.
Prehnite is a fairly strong crystal, quite resistant to pressures and scratching. It is composed of aluminum, calcium and silicon with a few specimens containing small trace of iron as well. It is considered a secondary or second stage mineral, meaning that the crystal did not form during the initial volcanic activity, but instead the crystals were form by events caused by the volcano, much after the fact.
Initially Prehnite was rare, South Africa being the only known location for many, many years. Eventually pockets of the stone were found throughout the world, including the US, Canada, Austria, Germany, France and India.