Diamond is the birthstone for April in the modern American birthstone list, a standard codified in 1912 by the American National Retail Jewellers Association (now Jewelers of America) and subsequently adopted across Western retail markets. As the hardest natural material known — rated 10 on the Mohs scale, a position it holds alone — diamond is simultaneously the most scientifically remarkable and commercially dominant gemstone in the world. Its assignment to April formalised an association between the stone and qualities of invincibility, clarity, and enduring love that had circulated in European gem lore for centuries.

The Birthstone Tradition

The modern birthstone list of 1912 was a trade-driven rationalisation of several competing historical lists, including those derived from the twelve stones of the High Priest's breastplate described in Exodus and from early astrological gem catalogues. The April–diamond pairing draws on a long Western tradition linking diamond with the planet Mars and with the virtue of fortitude. The Gemological Institute of America notes that earlier European lists sometimes assigned sapphire or opal to April, but by the early twentieth century diamond had become the dominant candidate in Anglo-American usage, a position the 1912 list made definitive. The Jewelers of America updated the list in 1952 and again in subsequent decades, but April's assignment has remained unchanged.

Gemmological Character

Diamond is pure carbon crystallised in the cubic system, typically formed at depths of 150 kilometres or more in the Earth's mantle under pressures exceeding 45 kilobars and temperatures above 900 °C. It is brought to the surface by kimberlite and lamproite volcanic pipes. Its exceptional hardness derives from the strength and uniformity of its tetrahedral carbon–carbon covalent bonds. Key optical and physical properties include:

• Refractive index: 2.417 (singly refractive, isotropic)
• Dispersion: 0.044 (fire), among the highest of any colourless natural gemstone
• Lustre: adamantine — a term derived from the Greek for diamond itself
• Hardness: 10 (Mohs); nonetheless exhibits perfect octahedral cleavage in four directions
• Specific gravity: approximately 3.52

Most gem diamonds are colourless to near-colourless, graded on the GIA D-to-Z colour scale. Stones outside this range — naturally coloured by structural defects or trace elements — are classified as fancy colour diamonds and command separate, often considerably higher, valuations.

Symbolism and Cultural Associations

The symbolic vocabulary attached to diamond — eternity, strength, incorruptibility — maps naturally onto the stone's physical properties. Its use in engagement rings, a custom popularised in fifteenth-century European aristocracy and entrenched in mass-market culture through twentieth-century advertising, has made diamond the most recognised symbol of romantic commitment in Western societies. For those born in April, the stone carries the additional personal resonance of a birthstone, a layer of meaning that has driven consistent demand for diamond jewellery as birthday and anniversary gifts.

Durability and Wearability

Diamond's Mohs 10 hardness makes it exceptionally resistant to scratching, and its chemical inertness means it is unaffected by most acids and household chemicals. These properties make it arguably the most practical of all birthstones for daily wear in rings, bracelets, and other pieces subject to abrasion. The principal care caveat is its cleavage: a sharp blow in the correct direction can cleave or chip a diamond, and stones should be protected from hard impacts. Ultrasonic and steam cleaning are generally safe for untreated diamonds set in stable mountings, though caution is warranted for stones with significant inclusions or fracture-filling treatments.

In the Trade

Diamond occupies a singular position in the gem trade, supported by grading infrastructure — the GIA's 4Cs system of cut, colour, clarity, and carat weight — that is more standardised than that of any other gemstone. April birthstone jewellery encompasses the full range of the market, from small melee-set pieces to significant solitaires. Laboratory-grown diamonds, chemically and physically identical to their mined counterparts, have entered the birthstone market at substantially lower price points, a development that has broadened accessibility without displacing demand for natural stones at the upper end of the market.

Further Reading

• GIA Diamond Overview — gia.edu
• GIA April Birthstone — gia.edu
• AGTA Birthstone Guide — agta.org