Prehnite

Prehnite is a calcium and aluminum inosilicate mineral with the formula Ca₂Al(OH)₂. It was discovered in 1789 by Dutch military Colonel Hendrik von Prehn, who it was named after. Prehnite is a secondary or hydrothermal mineral that can be found in igneous rocks and stalactite masses. It forms in spherical or globular masses and can be white, tan, green, or yellow.