Gem library
Sapphire
Corundum in every colour but red
Sapphire is corundum in every colour but red, which belongs to ruby. Hardness 9, no cleavage and total chemical stability make it the most resistant gem after diamond — and the best suited to daily wear.
- Hardness (Mohs)
- 9
- Density
- 3.95 – 4.03
- Crystal system
- Trigonal
- Refractive index
- 1.762 – 1.778
- Cleavage
- None (parting along twins)
Mineralogical identity
- Family
- Oxides — corundum group
- Species
- Corundum
- Variety
- Blue sapphire, padparadscha, star sapphire, fancy sapphire
- Chemical formula
- Al₂O₃ + Fe, Ti (blue)
- Crystal system
- Trigonal (rhombohedral)
- Classification
- Precious stone
- Rarity
- Very rare
- Indicative price
- €200 – 30,000/ct (Kashmir: far beyond)
Etymology
From the Greek sappheiros via Latin sapphirus — but in antiquity the word probably denoted lapis lazuli.
Physical & optical properties
- Hardness (Mohs)
- 9
- Density
- 3.95 – 4.03
- Refractive index
- 1.762 – 1.778
- Birefringence
- 0.008 – 0.010
- Cleavage
- None (parting along twins)
- Fracture
- Conchoidal to splintery
- Lustre
- Vitreous to subadamantine
- Diaphaneity
- Transparent to opaque
- UV fluorescence
- Weak
- Pleochroism
- Distinct
- Colours
- blue, pink, yellow, orange, green, colourless, purple
Formation, geology & history
One mineral, a whole spectrum
The classic blue arises from charge transfer between iron and titanium; yellow and orange from iron alone or from colour centres; pink from chromium; violet from a combination. Padparadscha, the pink-orange Sri Lankan sapphire named after the lotus flower, is among the most sought after in the world. Fancy sapphires — yellow, pink, peach, teal, green — have gained greatly in popularity since the 2010s, notably the blue-green teals of Montana and Australia. Sapphire also shows distinct pleochroism: violet-blue along one axis, greenish blue along the other, which the lapidary must orient correctly to maximise face-up colour.
Kashmir, Ceylon, Madagascar
Kashmir sapphires, mined between 1881 and 1887 at 4,500 metres at Padar, have a velvety cornflower blue due to fine rutile inclusions that scatter light. The deposit has been exhausted for over a century and certified Kashmir stones reach extraordinary prices at auction. Ceylon (Sri Lanka) has produced luminous pale blue sapphires and padparadschas for two millennia. Madagascar, which entered the market in the 1990s with the Ilakaka rush, is today the leading world producer. Each origin has its inclusion signature, which allows laboratories to determine it — and origin can multiply price tenfold.
Treatments and asterism
Like ruby, the great majority of sapphires are heated to dissolve rutile veils and intensify the blue; the treatment is stable and accepted, and the mention «unheated» multiplies value. Beryllium diffusion, which appeared in the early 2000s, artificially creates padparadschas and must always be declared. Star sapphires owe their six-rayed star to rutile needles aligned in three directions: they are cut as cabochons to reveal the asterism. Some even show a twelve-rayed star, from two generations of needles.
How to recognise it
- Distinct pleochroismRotate the stone: the blue shifts from violet to greenish along the axis. Glass and spinel have no pleochroism at all.
- Hardness 9It scratches topaz. A blue stone scratched by topaz is neither sapphire nor ruby.
- Density 4Appreciably heavy. Tanzanite (3.3), blue topaz (3.5) and glass (2.5) are lighter.
Imitations, treatments & confusions
- Verneuil synthetic sapphireMass-produced since 1902, at a few euros per carat. Curved growth striae, spherical bubbles, over-uniform colour. Ubiquitous in antique jewellery and watches.
- Blue glass and synthetic spinelGlass shows bubbles and a soft lustre; blue synthetic spinel, heavily used until the 1970s, is isotropic and therefore without pleochroism.
- Undeclared beryllium diffusionCreates artificial padparadschas and yellows. Detectable only in a laboratory; it is the main reason to demand a certificate above a few hundred euros.
Deposits & origins
Kashmir (Padar — the legendary velvety blue, now nearly exhausted), Burma (Mogok), Sri Lanka (Ceylon, worked for 2,000 years, and the padparadschas), Madagascar (Ilakaka, today's leading world producer), Australia, Thailand, Ethiopia, Montana (USA)
Care & precautions
- The easiest gem to care for after diamond: hot soapy water, brush, ultrasonic, steam — all permitted on a sound stone.
- Insensitive to sun, salt, common acids and household products.
- One reservation only: heavily fractured or glass-filled stones need the same care as treated rubies.
- At hardness 9 it scratches everything: store separately to protect other stones.
Traditions & crystal healing
- Chakras
- Third eye · throat
- Zodiac signs
- Virgo · Sagittarius · Taurus
- Element
- Air · Water
- Month
- September
A stone of wisdom and justice in tradition: it is said to support clear judgement, fidelity to one's word and detachment from the passions. Worn by bishops and magistrates in the West, it is associated in Indian tradition with Saturn, planet of rigour and the long term.
The virtues described here belong to tradition and cultural heritage. They are in no way medical advice and never replace a consultation.
Frequently asked questions
Are all sapphires blue?
No: sapphire exists in every colour except red, which is reserved for ruby. Pink, yellow, orange, green, violet, colourless, and the famous pink-orange padparadscha of Sri Lanka.
Is my sapphire heated?
Statistically yes: more than 90 % are. Heating is stable and accepted; it is the mention «unheated» on a certificate that makes the price difference, often by a factor of five to ten.
Is sapphire suitable for an engagement ring?
It is the best choice after diamond: hardness 9, no cleavage, insensitive to chemicals. Diana's and then Kate Middleton's ring is the most famous example.