Gem library
Aquamarine
The sailors' blue beryl
Aquamarine is the blue beryl, direct cousin of emerald but with the opposite character: where emerald is fissured and fragile, aquamarine is clear and robust. Its colour comes from iron, and its crystals reach considerable size.
- Hardness (Mohs)
- 7.5 – 8
- Density
- 2.66 – 2.80
- Crystal system
- Hexagonal
- Refractive index
- 1.564 – 1.596
- Cleavage
- Imperfect on {0001}
Mineralogical identity
- Family
- Silicates — cyclosilicates, beryl group
- Species
- Beryl
- Variety
- Aquamarine (Santa Maria, Santa Maria Africana, Maxixe)
- Chemical formula
- Be₃Al₂Si₆O₁₈ + Fe²⁺
- Crystal system
- Hexagonal
- Classification
- Semi-precious stone
- Rarity
- Uncommon
- Indicative price
- €20 – 500/ct (intense Santa Maria: up to €1,000/ct)
Etymology
From the Latin aqua marina, «sea water», for its colour — sailors of antiquity carried it as a talisman against storms.
Physical & optical properties
- Hardness (Mohs)
- 7.5 – 8
- Density
- 2.66 – 2.80
- Refractive index
- 1.564 – 1.596
- Birefringence
- 0.005 – 0.009
- Cleavage
- Imperfect on {0001}
- Fracture
- Conchoidal to splintery
- Lustre
- Vitreous
- Diaphaneity
- Transparent
- UV fluorescence
- None
- Pleochroism
- Weak
- Colours
- blue, blue-green, sky blue
Formation, geology & history
Beryl, a family of gems
Beryl is a beryllium cyclosilicate whose varieties each carry a gem name: emerald (green, chromium), aquamarine (blue, iron), morganite (pink, manganese), heliodor (yellow-green, trivalent iron), goshenite (colourless) and the very rare red beryl of Utah. All share the same structure of hexagonal rings of silicate tetrahedra, with channels that host water and alkalis. Aquamarine owes its blue to divalent iron in an octahedral site; heated between 400 and 450 °C, its greenish component disappears and the blue purifies — a near-universal, stable and accepted treatment. The rare Maxixe aquamarines, a deep blue from irradiation, have the major drawback of fading in daylight.
Giant, limpid crystals
Unlike emerald, which crystallises in tormented schists, aquamarine grows in pegmatite cavities where space is not lacking: crystals commonly exceed a metre. The largest known, found in Brazil in 1910, measured 48 cm across and weighed 110 kg. That is why large clean aquamarines are accessible, where a flawless ten-carat emerald would be a museum piece. The step emerald cut is the most used, since it showcases clarity and colour in depth; pale stones are cut deep to concentrate the tint.
Quality and market
Value rests almost entirely on the intensity of the blue. The term Santa Maria denotes a deep, slightly violet blue from the eponymous Brazilian deposit; Santa Maria Africana is its Mozambican equivalent. Pale aquamarines, very plentiful, are worth little. Beware trade names: «Nigeria aquamarine» or «Brazilian aquamarine» guarantee nothing in themselves. Shigar crystals from Pakistan, often associated with micas and tourmalines, are sought rough by collectors rather than cut.
How to recognise it
- Clean blue without marked greenAquamarine leans towards sky blue or a soft blue-green. An electric or saturated blue suggests treated topaz or glass.
- Rain-like inclusionsFine parallel channels, called «rain» or growth tubes, are typical of beryl and visible under a loupe.
- Hardness 7.5-8 and density 2.7It scratches quartz. Its moderate density distinguishes it from topaz (3.5), which is appreciably heavier.
Imitations, treatments & confusions
- Treated blue topaz sold as aquamarineThe confusion is frequent. Topaz is denser (3.5 against 2.7) and its blue more saturated and cold. Its price is also far lower.
- Blue glass and synthetic spinelGlass shows bubbles and no birefringence. Pale blue synthetic spinel, much used in antique jewellery, is isotropic.
- Irradiated Maxixe berylA magnificent deep blue but unstable: it fades in daylight within months. It must be declared.
Deposits & origins
Brazil (Minas Gerais — the Santa Maria de Itabira deposit, the benchmark for intense blue), Mozambique (Santa Maria Africana), Nigeria, Madagascar, Pakistan (Shigar valley, collector crystals), Zambia, Russia, China
Care & precautions
- Warm soapy water and a soft brush: aquamarine is solid and little fissured.
- Ultrasonic cleaning is acceptable on sound stones, but avoid it if liquid inclusions are visible.
- Avoid prolonged sunlight: aquamarines fade, and Maxixe stones lose their colour completely.
- The imperfect basal cleavage justifies protecting it from frontal impact despite its good hardness.
Traditions & crystal healing
- Chakras
- Throat
- Zodiac signs
- Pisces · Gemini · Aquarius
- Element
- Water · Air
- Month
- March
The stone of sailors and of calmed speech: tradition says it soothes storms, those of the sea as of the heart. It is credited with softening conflict, easing difficult conversations and giving a quiet courage — recommended equally to the shy and the talkative.
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
Aquamarine or blue topaz?
Three clues: topaz is far denser (3.5 against 2.7), of a more saturated cold blue, and much cheaper. Aquamarine has a soft blue and fine parallel needle inclusions.
Is my aquamarine heated?
Statistically yes: heating to 400-450 °C to remove the greenish cast is applied to almost all production. It is stable, undetectable and considered normal.
Why do some fade?
Maxixe beryls, coloured by irradiation, lose their blue in daylight. Classic aquamarines, coloured by iron, are stable but may lighten under prolonged intense sun.