Olivine, gem side up

Peridot is the gem name for transparent olivine, the magnesium‑ and iron‑silicate mineral that makes up much of Earth’s upper mantle. The chemistry is a series between forsterite (Mg end) and fayalite (Fe end). Peridot leans forsteritic, with enough Fe²⁺ to paint its signature green.

Name & old aliases

The word “peridot” likely traces to the Arabic farīdah (“gem”). Older texts may say chrysolite for greenish stones in general—today that term is out of fashion in gemology, and peridot is the keeper.

From the mantle with love

Olivine crystallizes deep in the mantle. Bits of peridotite and dunite are brought to the surface by basaltic eruptions and kimberlites, carrying peridot grains as gifts from depth.

Xenocrysts in basalt

Many gem peridots occur as xenocrysts—crystals caught up in volcanic rocks. Arizona’s San Carlos basalts and similar fields worldwide are classic sources of these green travelers.

Space editions

Some of the most jaw‑dropping peridot crystals come from pallasite meteorites, where olivine grew between iron‑nickel metal. They are rare in jewelry but famous in museums: gemstones from space.

Marbles & skarns (sometimes)

Peridot can also form in metamorphosed dolomitic limestones (skarns), where magnesium, silica, and heat team up under the right conditions.

Green‑sand beaches

Crushed olivine builds striking green beaches in a few places (hello, Hawaiʻi). Not gem grade, but a fun, walk‑on geology lesson.

History cameo

Egypt’s Red Sea island of Zabargad (St. John’s) supplied peridot for millennia—some historical “emeralds” were peridots from there. The glow gave it away under candlelight.

Palette

• Lime to apple green — classic peridot, lively and bright.
• Olive green — slightly deeper from higher Fe contents.
• Yellow‑green — warmer under incandescent light.
• Daylight shift — appears cleaner/greener under cool light.

Peridot rarely goes bluish—if the tone leans blue‑green, you’re probably looking at a different gem.

Pattern words

• Lily pads — circular stress halos around tiny crystals or gas bubbles.
• “Oil drops” — rounded liquid inclusions that add softness.
• Strain ripples — faint curved lines from internal stress.

Photo tip: A single point light at ~25–30° makes peridot’s brilliance snap and can show the famous doubling of back facets through the table.

“Lily pads”

At 10×, look for tiny crystals or bubbles ringed by disc‑like halos. They resemble lily pads on a pond—classic peridot scenery.

Facet doubling

Peer straight through the table at pavilion edges: you’ll often see a delicate double image (birefringence at work). Rotate to make it obvious.

Minor magnetism

Because of iron, some stones show a slight response to a strong neodymium magnet—a fun lab demo (not a diagnostic by itself).

Emerald (beryl)

Emerald tends more blue‑green, is harder (7.5–8), and lacks facet doubling. Its “jardin” inclusions differ from peridot’s lily pads.

Green garnet (demantoid/tsavorite)

Single‑refractive (no doubling). Demantoid shows strong fire and “horsetail” inclusions; tsavorite is richer, cooler green and harder.

Green tourmaline

Deeper tones, stronger pleochroism (yellow‑green ↔ blue‑green), different optic character; usually no lily pads.

Glass & synthetics

Glass shows bubbles and lacks doubling; synthetics (YAG/CZ) are denser, higher RI, and often too perfect. Peridot’s inclusions and RI range are a giveaway.

Chrome diopside

Deeper “pine” green; distinct cleavage and different RI; usually darker in larger sizes than peridot.

Quick checklist

• Yellow‑leaning green? ✓
• Facet doubling under the table? ✓
• Lily‑pad halos under 10×? Likely peridot.

Classic sources

Zabargad Island (Egypt) is legendary; Mogok (Myanmar) has produced fine crystals; modern supplies come from Pakistan (Kohistan), China, Vietnam, and the USA (Arizona’s San Carlos Reservation).

Space story

Pallasite meteorites sometimes hold gemmy olivine big enough to facet. These space peridots are rare curiosities—more museum piece than everyday jewel, but irresistible to mention.

Everyday care

• Clean with lukewarm water + mild soap; soft brush; dry promptly.
• Avoid ultrasonics/steam and sudden temperature swings.
• Keep away from acids and bleach; store separately to prevent scuffs from harder gems.

Jewelry guidance

• Great for pendants, earrings, dress rings. For daily‑wear rings, use protective bezels or halos.
• Peridot’s crown can abrade with time—polish touch‑ups restore the sparkle.
• Yellow gold warms the hue; white metals make it read crisper and greener.

On the wheel

• Peridot is brittle: use light pressure and keep it cool.
• Pre‑polish through 1200→3k→8k; finish with cerium or alumina for a glassy shine.
• Watch for orange‑peel on large flats—refresh laps and slow down; micro‑bevel edges to discourage chipping.

Facet double‑take

Hold a faceted stone under a loupe and look through the table: those doubled pavilion edges are peridot’s optical autograph.

Lily‑pad safari

With 10× magnification, hunt for circular halos around pinpoint crystals—tiny stress rings that look like pond pads at sunset.