June 21 – July 22 · Water

Cancer birthstones

Cancer carries Ruby and Moonstone in the zodiac tradition.

Ruby

Composition Aluminium oxide (Al₂O₃) — corundum coloured by chromium
Hardness · System 9 · Trigonal

Ruby and sapphire are the same mineral. Red corundum is ruby; every other colour is sapphire.

Traditionally associated with courage, appetite for life and decisive action.

Moonstone

Composition Potassium aluminium silicate (KAlSi₃O₈) — feldspar
Hardness · System 6–6.5 · Monoclinic

The floating blue glow is adularescence — light scattering between microscopic layers of two feldspars, not an inclusion or a coating.

Traditionally linked to intuition, cycles and new beginnings.

Sign or month?

Cancer runs June 21 – July 22, 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

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

Zodiac stones Ruby, Moonstone
Months it covers June and July
Stones of those months Pearl, Moonstone, Alexandrite, Ruby
In both systems Ruby, Moonstone

June 21 – July 22 — so the sign opens in one month and closes in another. Why the two lists never line up →

The split is uneven: 10 days fall in June and 22 in July. So most people with this sign — 69% — are sold the July stone.

Both stones — Ruby and Moonstone — also sit in the monthly list somewhere, which is the usual case.

June Pearl, Moonstone, Alexandrite July Ruby

The stones themselves

Stone Mohs Crystal system Main sources
Ruby 9 Trigonal Myanmar, Mozambique, Thailand
Moonstone 6–6.5 Monoclinic Sri Lanka, India, Madagascar

Moonstone is the softer at 6–6.5 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 →

Ruby

Aluminium oxide (Al₂O₃) — corundum coloured by chromium Traded along the Silk Road from Burma; Sanskrit called it ratnaraj, "king of gems"

Moonstone

Potassium aluminium silicate (KAlSi₃O₈) — feldspar Roman naturalists believed it was solidified moonlight