Prehnite is a hydrous silicate of alumina and lime, with bright, almost luminescent green coloring. It forms thick crusts with a rough or crystalline texture, and is commonly found in cavities and "pillows" along fractures of basalt.

In the early 18th century, Dutch mineralogist Colonel Hendrik Von Prehn (1733-1785) discovered it within Jurassic dolerite (volcanic rock) on the Cape of Good Hope, South Africa.

This stone has the distinction of being the first mineral named after a person.