The birthstone tradition assigns a specific gemstone to each month of the year. The modern list was standardized by the American National Retail Jewelers Association in 1912 and has been updated several times since, most recently with the addition of tanzanite for December in 2002 and spinel for August in 2016.
January: Garnet
Garnets come in every colour except blue. The deep red almandine and pyrope varieties are the most traditional, but green tsavorite and orange spessartite have gained popularity. Mohs hardness: 6.5 to 7.5. Suitable for all jewellery types.
February: Amethyst
Once considered as valuable as sapphire, amethyst became affordable after large Brazilian deposits were discovered in the 19th century. The finest colour is a deep, even purple with reddish flashes. Mohs hardness: 7.
March: Aquamarine
A member of the beryl family (along with emerald), aquamarine ranges from pale blue to blue-green. The most valued colour is a medium, slightly greenish blue. Unlike emerald, aquamarine is typically very clean. Mohs hardness: 7.5 to 8.
April: Diamond
The hardest natural material (Mohs 10), diamond is valued for its brilliance and fire. While colourless diamonds are the most familiar, fancy coloured diamonds in yellow, pink, blue, and green are among the rarest gemstones in existence.
May: Emerald
The green variety of beryl, coloured by chromium and sometimes vanadium. Inclusions are expected and accepted. The finest colour is a vivid, slightly bluish green. Mohs hardness: 7.5 to 8, but emeralds are brittle due to their typically fractured nature.
June: Alexandrite / Pearl
June has two birthstones. Alexandrite (chrysoberyl) changes colour from green in daylight to red under incandescent light. Pearl, the only organic birthstone, is formed inside mollusks and requires no cutting or polishing.
July: Ruby
Red corundum. The most valued colour is "pigeon blood red," an intense, slightly purplish red with strong fluorescence. Fine rubies above 3 carats are rarer than equivalent diamonds. Mohs hardness: 9.
August: Peridot / Spinel
Peridot is one of the few gemstones that occurs in only one colour: green, ranging from yellowish to brownish green. Spinel, added in 2016, comes in a range of colours and has historically been confused with ruby and sapphire.
September: Sapphire
While "sapphire" conjures blue, the stone actually occurs in every colour except red (red corundum is classified as ruby). The most valued colour is a vivid, medium-toned blue. Kashmir, Burmese, and Sri Lankan sapphires are the most prized origins.
October: Opal / Tourmaline
Opal displays play-of-colour, a shifting display of spectral colours caused by light diffracting through microscopic silica spheres. Tourmaline offers the widest colour range of any gem species, including bi-coloured and watermelon varieties.
November: Topaz / Citrine
Imperial topaz in orange to pinkish-orange is the most prized variety. Natural citrine (yellow to orange quartz) is rarer than most people realize; the majority of commercial citrine is heat-treated amethyst.
December: Tanzanite / Zircon / Turquoise
Tanzanite, found only in Tanzania, shows a violet-blue colour that rivals fine sapphire at a fraction of the price. Natural zircon (not cubic zirconia) is a beautiful, high-dispersion stone in blue, golden, and colourless varieties.
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