Discover the lore, properties, history, and buying considerations for the traditional Big Four—diamond, ruby, sapphire, and emerald—plus rare alexandrite.
Historically, the term "precious" was reserved for the Big Four—diamond, ruby, sapphire, and emerald—because of their rarity, cultural significance, and hardness. Modern gemology also includes alexandrite in this elite class. The distinction is traditional rather than purely scientific.
Compare each stone's measurable properties, history, traditional symbolism, and buying guidance.
Precious gemstone
The hardest known natural material on Earth, composed of pure carbon. Evaluated by the 4Cs: Cut, Color, Clarity, and Carat weight. The ultimate symbol of endurance and eternal love.
Mohs hardness: 10
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Precious gemstone
A red variety of the mineral corundum. Its fiery hue comes from trace amounts of chromium. The most valuable rubies historically originate from Burma.
Mohs hardness: 9
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Precious gemstone
Also a variety of corundum, coming in every color except red. The classic deep blue variants from Kashmir, Ceylon, and Montana are highly prized.
Mohs hardness: 9
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Precious gemstone
The green variety of the beryl family. Famous for internal characteristics known as 'jardin' (garden). Colombian emeralds are known for pure green hues.
Mohs hardness: 7.5
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Precious gemstone
Alexandrite is the chameleon of the gem world—vivid green in daylight, dramatic red or purple-red under incandescent light. This color change, caused by chromium in chrysoberyl, is so remarkable that gemologists describe fine specimens as 'emerald by day, ruby by night.'
Mohs hardness: 8.5
Read the Alexandrite profile