May 21 – June 20 · Air

Gemini birthstones

Gemini carries Pearl and Agate in the zodiac tradition.

Pearl

Composition Calcium carbonate (aragonite) in a matrix of conchiolin
Hardness · System 2.5–4.5 · Orthorhombic (aragonite)

Soft enough to scratch with a fingernail and dissolved by acid — perfume, vinegar and sweat all damage it.

Traditionally associated with sincerity, emotional maturity and quiet dignity.

Agate

Composition Banded chalcedony formed in volcanic cavities
Hardness · System 6.5–7 · Trigonal

The bands record successive deposits of silica in a gas bubble — each line is a separate episode of mineral-rich water passing through.

Traditionally associated with steadiness and gradual, unforced progress.

Sign or month?

Gemini runs May 21 – June 20, which crosses two calendar months — so the zodiac stone and the monthly birthstone may or may not agree depending on your exact date. Neither system overrules the other; the zodiac one is simply older.

Compare against the monthly chart →

← All zodiac birthstones

Two systems, one birth date

Gemini spans 2 calendar months, so you have more than one birthstone

Zodiac stones Pearl, Agate
Months it covers May and June
Stones of those months Emerald, Pearl, Moonstone, Alexandrite
In both systems Pearl

May 21 – June 20 — so the sign opens in one month and closes in another. Why the two lists never line up →

The split is uneven: 11 days fall in May and 20 in June. So most people with this sign — 65% — are sold the June stone.

Agate appears in no month at all — one of just four such stones across the twelve signs.

May Emerald June Pearl, Moonstone, Alexandrite

The stones themselves

Stone Mohs Crystal system Main sources
Pearl 2.5–4.5 Orthorhombic (aragonite) Japan, China, Australia
Agate 6.5–7 Trigonal Brazil, India, Germany

Pearl is the softer at 2.5–4.5 on the Mohs scale — below 7, which means household dust scratches it, so it belongs in earrings or a pendant rather than an everyday ring. What the scale means →

Pearl

Calcium carbonate (aragonite) in a matrix of conchiolin The only gem produced by a living animal; harvested since at least 2300 BCE in China

Agate

Banded chalcedony formed in volcanic cavities Named after the Achates river in Sicily, where Theophrastus recorded it around 300 BCE