Botryoidal prehnite

Pale green to yellow-green, translucent to opaque, with a vitreous to pearly luster and rounded, grape-like aggregates. Mohs hardness 6–6.5; orthorhombic crystal structure, typically without obvious cleavage; specific gravity about 2.8–3.0. The image’s rounded pale nodules are consistent with prehnite, though identification from the image alone is not certain.

Forms in low-temperature hydrothermal veins and cavities in basalt and other mafic volcanic rocks, commonly alongside zeolites. Its age depends on the host rock and local geological history.

Used as a decorative and collector mineral; attractive translucent material is cut into cabochons and beads. It has limited industrial use.

Prehnite was among the first minerals named after a person, Colonel Hendrik von Prehn, in the late 18th century.

Look for pale green, compact botryoidal masses lining basalt cavities, often associated with zeolites. Common sources include South Africa, Australia, India, and the United States.