Rough prehnite with a distinctive dusting of epidote crystals which are present primarily on one side of this mineral specimen. Although this piece was mined in South Africa, prehnite can be found in many other localities worldwide.
On Mohs scale of mineral hardness prehnite grades 6 to 6½ so it's quite hard but is also brittle so cutting it as a gemstone can be a challenge. Although translucent to transparent, stones can also be cloudy so they're not hugely popular for use in items of jewellery.
Weight (grams): 740
Size (cms): 11.6 x 8.9 x 9.9