Coloured Gemstones
Sapphires, emeralds, rubies, and the gems that mark our months. A guide to colour, character, and what your stone can hold beyond beauty.
A coloured gemstone is, more than any other stone, a piece of personality. Where a diamond is brilliance, a gemstone is mood — colour, depth, and a kind of warmth that can only be felt, never explained.
Why coloured stones matter.
Long before diamonds came to dominate the engagement ring, fine jewellery belonged to the world of coloured gemstones. Royalty wore rubies. Renaissance hands wore emeralds. Sapphires marked the most enduring vows in history.
A coloured gemstone offers something a diamond cannot — an immediate, undeniable mood. Colour speaks before the stone is even in focus. The deep green of an emerald, the cool steady blue of a sapphire, the velvet red of a ruby — each carries centuries of meaning, and yet remains intensely personal to whoever wears it.
"A diamond is brilliance. A coloured gemstone is mood — colour, depth, and a kind of warmth that can only be felt, never explained."
Sapphire, emerald, ruby.
Three stones — known together as the precious coloured gemstones — that have defined fine jewellery for over a thousand years. At Stara, these are the most commonly chosen alongside diamonds for engagement rings, bespoke pieces, and high jewellery commissions.
Sapphire
Corundum (Al₂O₃)The stone of wisdom and royalty. Hardness of 9. Found across the globe in blues, pinks, yellows, and rarest of all — padparadscha.
Emerald
Beryl (Be₃Al₂Si₆O₁₈)The green of renewal and renaissance. Hardness 7.5–8. Treasured for its inner garden — natural inclusions called jardin.
Ruby
Corundum (Al₂O₃)The blood-red gem of love and courage. Hardness 9. The rarest fine ruby — a "pigeon-blood" red — is among the most valuable stones on earth.
Understanding hardness.
Gemstone hardness is measured on the Mohs scale — a system from 1 (talc, the softest) to 10 (diamond, the hardest). Hardness affects how well a stone resists scratching during everyday wear. For an engagement ring worn daily, hardness matters more than for a pendant worn occasionally.
Where common stones fall on the Mohs scale
Stones rated 7 and above are generally suitable for daily wear in rings.
The classic stones, in depth.
Sapphire
Corundum — Al₂O₃Although traditionally associated with deep cornflower blue, sapphires occur in nearly every colour except red (a red corundum is, by definition, a ruby). Pinks, yellows, greens, purples, oranges, and the rare salmon-pink padparadscha are all sapphires. Most blue sapphires owe their colour to traces of titanium and iron.
Sapphire is exceptionally durable, second only to diamond. This makes it among the very best choices for an engagement ring — particularly for those who want colour without compromising on everyday wearability. Famously the centre stone in the engagement ring of the late Princess Diana, now worn by Catherine, Princess of Wales.
Emerald
Beryl — Be₃Al₂Si₆O₁₈The vivid green of an emerald comes from trace chromium and vanadium. Where diamonds are valued for clarity, emeralds are accepted to have natural internal characteristics — called the jardin (French for "garden") — visible to the naked eye. These inclusions are part of the stone's identity, not flaws.
Emeralds are softer and more brittle than sapphires or rubies, so they require slightly more thoughtful daily wear. Most natural emeralds are oiled or resin-treated to enhance their clarity — an industry-standard practice that should always be disclosed at point of sale.
Ruby
Corundum — Al₂O₃A ruby is a red sapphire — same mineral, different element causing the colour. Where blue sapphire takes its hue from titanium and iron, ruby owes its red to chromium. Beyond a certain pinkness threshold, the stone is classified as a pink sapphire rather than a ruby; the line is genuinely subtle.
The most prized rubies come from Mogok in Myanmar, where the chromium content produces a deep red with a slight blue undertone — what gemologists call "pigeon-blood red." Top-quality rubies command higher prices per carat than diamonds, and fine rubies above three carats are exceptionally rare.
Birthstones through the year.
The tradition of birthstones traces back to ancient times — possibly to the breastplate of Aaron in the Book of Exodus, with twelve stones representing twelve tribes. The modern list of birthstones used today was standardised in 1912 by the American National Association of Jewelers, with later additions reflecting newly available gemstones.
Garnet
Deep red. Hardness 6.5–7.5. Symbol of trust and friendship.
Amethyst
Royal purple. Hardness 7. Believed to bring clarity and calm.
Aquamarine
Sea-glass blue. Hardness 7.5–8. Stone of courage and serenity.
Diamond
Colourless brilliance. Hardness 10. Eternal love, strength, purity.
Emerald
Vivid green. Hardness 7.5–8. Symbol of rebirth, love, fertility.
Pearl & Alexandrite
Pearl: hardness 2.5–4. Alexandrite: 8.5, colour-changing.
Ruby
Pigeon-blood red. Hardness 9. Stone of passion and protection.
Peridot
Olive green. Hardness 6.5–7. Said to bring good fortune.
Sapphire
Royal blue. Hardness 9. Wisdom, faithfulness, and truth.
Opal & Tourmaline
Opal: hardness 5–6.5, iridescent. Tourmaline: 7–7.5, multi-coloured.
Topaz & Citrine
Topaz: hardness 8, in many colours. Citrine: 7, golden yellow.
Tanzanite, Turquoise & Zircon
Tanzanite: 6.5–7. Turquoise: 5–6. Zircon: 7.5.
A note on treatments.
Most coloured gemstones available today have undergone some form of standard industry treatment to enhance colour or clarity. At Stara, we will always tell you exactly what your stone has been through.
Heating
The most common treatment, particularly for sapphires and rubies. Stable, permanent, and considered standard. Untreated stones with natural beauty are rarer and more valuable.
Oiling
Standard for emeralds. Cedar oil or resin fills natural fissures to improve clarity. Should be re-oiled every few years to maintain. Always disclosed.
Beryllium / Surface diffusion
Adds colour to sapphires and rubies. Significantly affects value — a diffused stone is worth a fraction of an untreated one. Always disclosed at Stara.
Laboratory-created gemstones
Lab-grown sapphires, rubies, and emeralds are chemically identical to natural. Significantly more affordable and offered at Stara as a transparent alternative.
Other gemstones we love.
Beyond sapphire, emerald, and ruby, fine jewellery makes use of a wider palette of remarkable stones. Each carries its own character, durability, and price profile.
Spinel — long mistaken for ruby, recently rediscovered as one of the most beautiful red stones in jewellery. Hardness 8. Excellent for daily wear and growing rapidly in collector demand.
Tourmaline — the gemstone of countless colours. Pink, green, watermelon (bicolour), Paraíba (electric neon blue). Hardness 7–7.5. Striking and increasingly fashionable.
Tanzanite — found only in one small region of Tanzania. Vivid violet-blue. Hardness 6.5–7, so somewhat softer. Mining is finite — supply may run out within decades.
Aquamarine — clear sea blue, member of the beryl family alongside emerald. Hardness 7.5–8. Often available in larger sizes than emerald and at more accessible prices.
Morganite — soft pink beryl, popularised in modern romantic engagement rings. Hardness 7.5–8. A more affordable alternative to pink sapphire or pink diamond.
How we source your stone.
Coloured gemstones are sourced for our clients privately, by appointment. The reason is not exclusivity — it's quality. Coloured stones vary enormously in tone, saturation, treatment, and origin in ways that simply cannot be conveyed in a website thumbnail. The right stone is the one you see in person, or through a guided virtual viewing where we walk you through every detail.
We work with trusted gemstone dealers across multiple origins and curate options based on your specific design, colour preference, and budget. Every stone comes with full disclosure of treatments and origin. Where applicable, certifications are provided.
There is no obligation to proceed and no deposit required to begin the conversation.