Prehnite

Prehnite is an inosilicate of calcium and aluminum. It crystallizes in the orthorhombic crystal system and is most often found as stalactite or botryoid aggregates. Its hardness is 6-6.5. The color ranges from light green to yellow, but also colorless, blue, pink or white. In April 2000, a rare orange prehnite was discovered in the Kalahari Manganese fields of South Africa. Prehnite is mostly translucent and rarely transparent. It was first described in 1788 for occurrence in the Karoo dolerites of Cradock, Eastern Cape Province, South Africa. It was named after Colonel Hendrik Von Prehn.