Gem library
Emerald
The green beryl with a garden of inclusions
Emerald is one of the four precious stones, and the most paradoxical: its value rests on a unique colour produced by chromium, yet it is almost always fissured. Its inclusions, poetically called the «garden», are the mark of its authenticity.
- Hardness (Mohs)
- 7.5 – 8
- Density
- 2.67 – 2.78
- Crystal system
- Hexagonal
- Refractive index
- 1.565 – 1.602
- Cleavage
- Imperfect on {0001}, but numerous fractures
Mineralogical identity
- Family
- Silicates — cyclosilicates, beryl group
- Species
- Beryl
- Variety
- Emerald
- Chemical formula
- Be₃Al₂Si₆O₁₈ + Cr, V
- Crystal system
- Hexagonal
- Classification
- Precious stone
- Rarity
- Very rare
- Indicative price
- €300 – 20,000/ct (exceptional Colombians: beyond)
Etymology
From the Greek smaragdos via Latin smaragdus, «green stone», from a Semitic root denoting brilliance.
Physical & optical properties
- Hardness (Mohs)
- 7.5 – 8
- Density
- 2.67 – 2.78
- Refractive index
- 1.565 – 1.602
- Birefringence
- 0.005 – 0.009
- Cleavage
- Imperfect on {0001}, but numerous fractures
- Fracture
- Conchoidal to splintery
- Lustre
- Vitreous
- Diaphaneity
- Transparent to translucent
- UV fluorescence
- Weak
- Pleochroism
- Weak
- Colours
- green, bluish green, deep green
Formation, geology & history
A gem born of a geological impossibility
Emerald requires the meeting of two elements that never travel together: beryllium, native to evolved granitic crust, and chromium or vanadium, typical of ultrabasic mantle rocks. A tectonic anomaly is therefore needed to bring them together. In Colombia it is hydrothermal brines circulating through organic-rich black shales along thrust faults — a context unique in the world, which explains Colombian quality. Elsewhere emeralds form at the contact of pegmatites and ultrabasic rocks (Zambia, Brazil, Urals). This formation under tectonic stress also explains the fractures: the crystal grew in a moving environment.
The garden and oiling
Almost every emerald contains inclusions: three-phase cavities (liquid, gas, salt crystal) characteristic of Colombia, needles, pyrite or calcite crystals, and above all fissures. To improve transparency, those fissures are filled with a substance of similar refractive index — traditionally cedar oil, today resins such as Opticon or Palmajong. The process is ancient, nearly universal (over 90 % of market emeralds) and accepted, but it must be declared and graded: minor, moderate, significant. It is not permanent: oil evaporates or whitens, and an emerald may need re-oiling after a few decades.
History and the emerald cut
Cleopatra's mines in the Egyptian Eastern Desert produced emeralds from 1500 BC — of mediocre quality, but heavy with prestige. The Spanish conquest of the sixteenth century transformed the market with the discovery of Muzo and Chivor: Colombian emeralds flooded Europe and then, through Portuguese trade, reached the Mughal treasuries where they were engraved with verses. The emerald cut — rectangular with steps and cut corners — was designed precisely for this stone: the cut corners protect the angles, its weakest points, and the steps minimise internal stress during polishing.
How to recognise it
- The garden of inclusionsA perfectly clean emerald is suspect: virtually all natural stones show inclusions under a loupe. Three-phase cavities are a Colombian marker.
- Weak red fluorescence under a Chelsea filterChromium produces a reddish tint under the Chelsea filter in many natural emeralds — a classic clue, though not decisive alone.
- Bluish green, never frankly yellowishAn olive or yellowish green points to peridot or green tourmaline. Emerald leans towards blue.
Imitations, treatments & confusions
- Synthetic emerald (Chatham, Gilson, Biron)Grown by flux or hydrothermally since the 1930s. Chemically identical, often too clean, with veil-like or zigzag inclusions typical of the process. A laboratory is needed.
- Doublets and tripletsTwo pieces of quartz or pale beryl bonded with green glue. Look for the bond line on the girdle and colour concentrated in one plane.
- Green glass and dyed quartzBubbles, no birefringence, a softer lustre. Green quartz («Brazilian emerald») is a misleading trade name.
Deposits & origins
Colombia (Muzo, Chivor, Coscuez — the world benchmark, slightly bluish green), Zambia (Kagem: darker and bluer, very clean), Brazil (Belmont), Ethiopia, Afghanistan (Panjshir), Zimbabwe (Sandawana), Russia (Urals), Egypt (Cleopatra's mines, exhausted)
Care & precautions
- Never ultrasonic cleaning, never steam: these methods drive out the filling oil or resin and abruptly reveal the fissures. It is the most costly error in jewellery.
- Clean with warm water and a soft cloth, no harsh soap or solvent. Dry at once.
- Avoid thermal shock and detergents; take the ring off for washing up and housework.
- Plan a check and possible re-oiling every ten to twenty years with a professional.
Traditions & crystal healing
- Chakras
- Heart
- Zodiac signs
- Taurus · Cancer · Gemini
- Element
- Earth · Water
- Month
- May
A stone of the heart and of knowledge in tradition: it is credited with emotional clarity, fidelity and renewal. The Romans dedicated it to Venus, the Incas to the serpent god, and medieval tradition held that it rested the eyes — stonecutters looked at an emerald to relax their sight.
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
Why does my emerald have fissures?
Because that is its nature: it crystallised in an active tectonic setting. More than 90 % of emeralds are fissured and oiled to improve transparency. An emerald with no inclusions is probably synthetic.
Can an emerald be cleaned in an ultrasonic bath?
Absolutely not. Vibration drives the oil or resin out of the fissures and can even propagate a fracture. Warm water and a soft cloth only.
Colombia or Zambia?
The Colombian has a warm, slightly bluish green and three-phase inclusions; the Zambian is darker, bluer and often cleaner. Both are excellent; the Colombian keeps a prestige premium.