What Is Prehnite? The First Mineral Ever Named After a Person

Prehnite is a calcium aluminum silicate mineral, typically pale to medium green (though it also occurs yellow, colorless, and rarely other colors), and it holds a genuine distinction in the history of mineralogy: it was the first mineral ever formally named after a person.

The Naming History

Prehnite is named after Colonel Hendrik Von Prehn, a Dutch military officer and mineral collector who brought specimens of the stone back from the Cape of Good Hope in the late 18th century. When the mineral was formally described and named in 1788, it set a naming precedent — using a person's name for a mineral — that has since become a common (though not universal) convention in mineralogy.

Often Mistaken for Other Green Stones

At a casual glance, prehnite's soft green color can be mistaken for peridot or light jade, but it's chemically and structurally unrelated to either — it belongs to its own distinct mineral group, and its slightly waxy-to-vitreous luster and typical botryoidal (grape-cluster-like) growth habit, which is where its name in some languages referencing "grape stone" comes from, generally distinguish it on closer inspection.

Epidote Inclusions

Prehnite often contains needle-like black or dark green inclusions of epidote, a related mineral that frequently grows alongside it — rather than being a flaw, these inclusions are common enough in prehnite that their presence or pattern is often considered part of the stone's natural character rather than something to avoid.

Where It's Mined

South Africa (near the original Cape of Good Hope locality) and Australia are major sources of gem and specimen-quality prehnite.

Quick Facts

Composition: calcium aluminum silicate — Hardness: 6–6.5 on the Mohs scale — First mineral ever named after a person (1788) — Often contains epidote inclusions — Major sources: South Africa, Australia.