Name with a story

Prehnite is widely cited as the first mineral formally named after a person: Colonel Hendrik von Prehn, who encountered the stone in the late 1700s at the Cape of Good Hope (South Africa). The name stuck—so did the color, which became a favorite for engraved gems in the 19th century.

Not a zeolite (but best friends)

Although it often forms with zeolites in basalt pockets, prehnite is not a zeolite. It’s a phyllosilicate with sheets of silicate tetrahedra linked by calcium and aluminum—more like a tidy stack of pages than a sponge.

Basalt bubble art

When lava solidifies, it preserves vesicles—frozen bubbles later filled by mineral‑rich waters. Prehnite precipitates along those cavities, building botryoidal or stalactitic layers with fellow cavity‑dwellers like apophyllite, stilbite, and calcite.

Metamorphic seams

In low‑grade metamorphism (the prehnite‑pumpellyite facies), this mineral grows in veins and fractures, often with epidote and pumpellyite—green companions in a gentle P‑T regime.

Silica & calcium handshake

Prehnite’s chemistry—Ca₂Al(AlSi₃O₁₀)(OH)₂—tells you what it needs: calcium‑bearing fluids, aluminum and silica, and a calm geologic setting that allows stacked sheets to assemble leisurely.

Palette

• Apple‑green — the classic, tranquil hue.
• Yellow‑green — warmer notes in some localities.
• Grey‑green / milky — where micro‑inclusions scatter light.
• Light shift — cooler in daylight, warmer under incandescent light.

Prehnite is prized for its translucency. Thin domes “lantern up,” a soft glow that reads expensive even in modest sizes.

Pattern words

• Botryoidal — grape‑like clusters with micro “peel” texture.
• Radial sprays / fans — spherulites that sometimes yield cat’s‑eye effects.
• Epidote needles — deep green spears through pale prehnite (Mali favorites).
• Chalcedony skins — thin quartz coats adding glassy luster to nodules.

Photo tip: Backlight a cab at ~30° to wake the inner “lantern,” then add a soft front fill to show surface texture without glare.

Surface & structure

On botryoidal pieces, look for a fine peel‑like texture. Cleavage faces are slightly silky/pearly, a different sheen than the glassy polish.

Inclusions

Common: fluid inclusions, wispy veils, and the occasional epidote needle. In cat’s‑eye pieces, dense, aligned fibers create a moving band of light.

Zoning & growth

Radial spherulites sometimes show growth zoning—concentric bands of faintly different translucency or tint, especially under backlight.

Chrysoprase (chalcedony)

Similar apple‑green but waxy luster, microcrystalline texture, and no cleavage flashes. Chrysoprase color is Ni‑based; prehnite’s is structural/trace‑driven.

Jade (nephrite/jadeite)

Jade feels denser, with a fibrous (nephrite) or granular (jadeite) micro‑structure and higher toughness. Prehnite is often mislabeled “new jade” in bead trades—note the misnomer.

Serpentine

Softer (can scratch with a knife), often greasy luster, and different SG. Serpentine commonly sold as “new jade” as well; it’s a separate family.

Calcite/aragonite

Much softer (3–3.5), strong reaction to acid, and different feel. Prehnite won’t fizz like that and holds a polish better.

Glass/resin

Too even in color, mold seams, and bubbles. Real prehnite shows minute inclusions, subtle zoning, and natural surface variations.

Quick checklist

• Translucent apple‑green with a waxy‑vitreous glow?
• Weak/absent pleochroism; possible cleavage sheen?
• Botryoidal origin or epidote needles? → Prehnite likely.

Where it shines

Classic pockets occur in the Deccan Traps of India (Maharashtra)—famous for sculptural clusters with apophyllite and stilbite. Other notable sources include South Africa (historic Cape Province localities), Mali (prehnite with epidote), the USA (New Jersey traprock quarries, parts of New England), China, Australia, and Europe (Alpine metamorphic zones).

Cabochon favorites

Most jewelry pieces are domed cabs cut from botryoidal masses. Placing the dome over the most translucent “grape” makes the stone appear lit from within—nature’s built‑in mood light.

Everyday care

• Clean with lukewarm water + mild soap; soft cloth; dry well.
• Avoid ultrasonics/steam and sudden temperature swings.
• Store separately; corundum/diamond neighbors can haze the polish over time.

Jewelry guidance

• Wonderful for pendants, earrings, dress rings. For daily‑wear rings, choose protective bezels and mindful habits.
• Open backs boost the glow; white metals read cool, yellow metals add lemon warmth.
• Cat’s‑eye prehnite benefits from tall domes and a single directional light.

On the wheel

• Prehnite can “orange‑peel” if rushed—keep laps clean, pressure light, and cooling steady.
• Pre‑polish 1200→3k→8k thoroughly; finish with cerium or alumina on a firm pad for a glassy‑waxy luster.
• Watch for cleavage—avoid thin edges across the plane; micro‑bevel girdles to discourage flakes.

Backlight “lantern”

Set a small flashlight behind a cab. That soft halo is prehnite’s signature—guaranteed to win over even the “I only like sparkly gems” crowd.

Texture safari

On a raw nodule, skim raking light across the surface. The micro “grape‑skin” texture leaps out, a perfect teachable moment about botryoidal growth.