Gem library
Amethyst
The bishops' violet quartz
Amethyst is the violet variety of quartz and by far the most famous of the semi-precious stones. Its colour comes from traces of iron subjected to the natural radiation of the surrounding rock: a geological accident that became the most sought-after hue in the mineral kingdom.
- Hardness (Mohs)
- 7
- Density
- 2.63 – 2.65
- Crystal system
- Trigonal
- Refractive index
- 1.544 – 1.553
- Cleavage
- None
Mineralogical identity
- Family
- Quartz — silica group
- Species
- Quartz
- Variety
- Amethyst
- Chemical formula
- SiO₂
- Crystal system
- Trigonal (rhombohedral)
- Classification
- Semi-precious stone
- Rarity
- Common
- Indicative price
- €2 – 25/ct
Etymology
From the Greek amethystos, «not drunken» — the ancients drank from amethyst cups to resist wine.
Physical & optical properties
- Hardness (Mohs)
- 7
- Density
- 2.63 – 2.65
- Refractive index
- 1.544 – 1.553
- Birefringence
- 0.009
- Cleavage
- None
- Fracture
- Conchoidal
- Lustre
- Vitreous
- Diaphaneity
- Transparent to translucent
- UV fluorescence
- Weak
- Pleochroism
- Weak
- Colours
- violet, purple, mauve
Formation, geology & history
Formation and geology
Amethyst grows in cavities within volcanic rock — mostly basalt — where silica-rich hydrothermal water circulates. As it cools, quartz crystallises inward from the cavity walls, which explains the classic geode structure: a grey crust outside, a forest of violet points inside. The colour requires the simultaneous presence of iron (Fe³⁺ or Fe⁴⁺ depending on the model) and natural irradiation from radioactive elements in the host rock. The great geodes of Artigas, Uruguay, formed inside the Paraná basalt flows roughly 130 million years ago.
Colour and zoning
The colour ranges from an almost colourless lilac to the deep purple known as «Deep Russian». It is almost never even: held against the light, an amethyst reveals banded or chevron zoning inherited from its layer-by-layer growth. The most intense crystals concentrate colour in the tip, which is why lapidaries often cut the gem from the top of the prism. Heated between 400 and 500 °C, amethyst becomes citrine — the origin of virtually all the citrine on the market. Heated only partly, it produces ametrine, violet and gold within the same crystal.
History and culture
Long counted among the precious stones, amethyst lost that rank in the nineteenth century when the colossal Brazilian deposits were found: the price collapsed within decades. It remains the bishops' stone, worn in the pastoral ring, and appears in the high priest's breastplate described in Exodus. Catherine the Great had it collected in the Urals, and the ancient Greeks saw it as a bulwark against drunkenness. Its popularity today owes as much to its price as to its beauty: it is the first stone in almost every collection.
How to recognise it
- Zoning against the lightHold the stone in front of a lamp: uneven bands or chevrons of colour are the signature of natural amethyst. A perfectly uniform violet should raise suspicion.
- Hardness 7It scratches glass effortlessly and resists a steel file. A violet stone scratched by a knife is not amethyst (think fluorite, hardness 4).
- No bubblesUnder a 10× loupe, look for mineral inclusions, veils or «fingerprints». Round bubbles mean cast glass.
Imitations, treatments & confusions
- Dyed glassVery common in cheap beads and pendants. The colour is too uniform, spherical bubbles show under the loupe, facet edges are rounded, and it feels warm rather than cool to the touch.
- Synthetic quartzGrown in autoclaves since the 1970s, chemically identical and impossible to separate by eye. Only a laboratory can rule. At a low price, assume doubt exists.
- Heated or irradiated amethystArtificial irradiation intensifies the colour; it is not fraud if declared, but it must be. An unreal neon shade is suspect.
Deposits & origins
Brazil (Artigas and Rio Grande do Sul), Uruguay (very high-colour geodes), Zambia (deep reddish violet), Madagascar, Bolivia (ametrine), India, Mexico, France (Auvergne, Vosges)
Care & precautions
- Warm soapy water and a soft brush: perfect. Brief rinsing only, never long soaking.
- Never direct sunlight: amethyst fades irreversibly within months behind a window.
- Avoid ultrasonic cleaners on fractured or filled stones, and any heat source above 200 °C.
- Store separately: at hardness 7 it scratches most other stones and is scratched by topaz and corundum.
Traditions & crystal healing
- Chakras
- Third eye · crown
- Zodiac signs
- Aquarius · Pisces
- Element
- Air
- Month
- February
Crystal-healing tradition makes it the great regulator of the mind: it is said to quiet looping thoughts, encourage peaceful sleep and support people breaking a habit — a direct echo of its Greek etymology. It is recommended to beginners for its gentleness, often placed on the bedside table.
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
Does amethyst lose its colour?
Yes, in direct sunlight and heat. An amethyst left on a windowsill fades within months, and the change is irreversible. Keep it in the shade.
What is the difference between amethyst and charoite?
Charoite is a rare Siberian silicate: opaque, fibrous, swirled, hardness 5. Amethyst is a transparent to translucent quartz of hardness 7. No confusion is possible under a loupe.
What is an amethyst worth?
From €2/ct for a common pale violet to €25/ct and beyond for an intense, clean, well-cut purple. Large sizes do not raise the price as steeply as they do for rare gems.