Amethyst Properties: Hardness, Colour, Fluorescence and Care
Amethyst is one of the best-known and most highly valued varieties of quartz. It is recognised by its violet colour, which can range from pale lilac and lavender to intense purple and deep reddish violet.
In modern crystal traditions, amethyst is associated with reflection, balance and mental clarity. It is also an interesting gemstone from a mineralogical perspective because of its colour centres, crystal structure, distinctive colour zoning and response to heat.
💎 Interested in amethyst? Explore amethyst crystals, jewellery, clusters and polished stones. View the collection →What is amethyst?
Amethyst is the purple variety of the mineral quartz. Its chemical composition is silicon dioxide, written as SiO₂.
Quartz occurs in many colours and forms. Other familiar quartz varieties include:
- clear quartz
- rose quartz
- smoky quartz
- citrine
- ametrine
- prasiolite
- chalcedony and its many varieties
Mineralogically, amethyst has the same basic composition and hardness as clear quartz. Its violet colour is what distinguishes it as a named quartz variety.
If you are interested in its traditional symbolism, read Amethyst Meaning.
Amethyst properties at a glance
- Mineral: quartz
- Chemical composition: silicon dioxide, SiO₂
- Colour: pale lilac to deep reddish purple
- Mohs hardness: 7
- Crystal system: trigonal
- Typical external habit: six-sided prisms with pointed terminations
- Lustre: vitreous
- Transparency: transparent to translucent
- Cleavage: none
- Fracture: commonly conchoidal
- Specific gravity: approximately 2.65–2.66
- Refractive index: approximately 1.544–1.553
- UV fluorescence: usually inert
What causes amethyst’s purple colour?
The colour of amethyst is connected with trace amounts of iron incorporated into the quartz structure and the formation of colour centres through natural irradiation.
It is therefore not entirely accurate to say that darker amethyst simply contains more iron. The final colour depends on how iron occurs within the crystal structure, the creation of colour centres, natural irradiation and the conditions in which the crystal formed.
Amethyst can display:
- pale pinkish violet
- lavender
- bluish purple
- reddish purple
- deep violet that appears almost black in dim lighting
Fine faceted amethyst is usually valued for strong, even purple colour. Collectors of rough crystals may instead appreciate visible colour zoning, unusual inclusions and differences between the crystal core, faces and termination.
Why does amethyst show colour zoning?
The purple colour in amethyst is often distributed unevenly. Darker colour may concentrate in growth zones beneath particular crystal faces, especially near the termination.
This can produce:
- alternating pale and dark bands
- triangular or angular colour zones
- phantom-like internal layers
- darker edges or crystal tips
- pinwheel-like patterns when viewed from above
Colour zoning is common in natural amethyst and can reveal how the crystal grew. In a faceted gemstone, strong uneven zoning may reduce commercial value because cutters generally seek an even face-up colour.
In a mineral specimen, however, zoning can be an attractive and informative feature rather than a flaw.
Is amethyst pleochroic?
Amethyst can show weak to moderate pleochroism. This means that slightly different purple or reddish-purple colours may be visible when the crystal is viewed from different crystallographic directions.
Pleochroism is easier to observe in transparent faceted stones with gemological equipment. It should not be confused with colour zoning, which is caused by an uneven distribution of colour within the crystal.
Amethyst hardness
Amethyst has a hardness of 7 on the Mohs scale. This gives it good resistance to scratching and makes it suitable for many types of jewellery.
The Mohs scale compares the relative scratch resistance of minerals:
- fingernail: approximately 2.5
- calcite: 3
- fluorite: 4
- feldspar: approximately 6
- quartz and amethyst: 7
- topaz: 8
- corundum, including ruby and sapphire: 9
- diamond: 10
The scale is not linear. Diamond is not merely a little harder than corundum, even though the numbers are adjacent.
Steel objects vary considerably in hardness, so a knife or nail is not a reliable tool for identifying amethyst. Scratch testing can also permanently damage a polished stone or specimen.
Hardness is not the same as toughness
Hardness describes resistance to scratching. Toughness describes resistance to breaking, chipping and impact.
Amethyst has no cleavage, meaning that it does not have a particular crystal plane along which it separates as readily as minerals such as fluorite or moonstone. It can nevertheless fracture when dropped or struck.
Crystal points, thin edges and pieces containing fractures require particular care. A rough cluster can be more vulnerable to physical damage than a rounded tumbled stone, even though both have the same Mohs hardness.
Does amethyst fluoresce under UV light?
Amethyst is generally inert under both long-wave and short-wave ultraviolet light. In other words, most amethyst does not produce a strong visible glow under a standard gemological UV lamp.
Occasional specimens may display a faint or unusual reaction because of inclusions, coatings, associated minerals or differences in composition. A visible response should therefore be assessed carefully rather than assumed to be a normal feature of amethyst.
Fluorescence is the emission of visible light while a material is exposed to ultraviolet radiation. It is different from phosphorescence, in which the visible emission continues after the UV source has been switched off.
Can UV light identify genuine amethyst?
No. UV fluorescence is not a reliable test for distinguishing natural amethyst from synthetic quartz, glass or another purple material.
Natural and laboratory-grown amethyst can both be inert. Some imitations may also show little or no reaction. Reliable identification may require refractive-index measurements, specific-gravity testing, polarised-light observations and microscopic examination by a gemologist.
UV safety
Do not look directly into a UV lamp or expose skin unnecessarily. Short-wave UV equipment requires particular caution and should be operated according to the manufacturer’s safety instructions.
Amethyst crystal structure
Quartz belongs to the trigonal crystal system. Amethyst is often described as having hexagonal crystals because its external habit commonly appears as a six-sided prism.
The distinction is useful:
- Crystal system: trigonal
- Common external appearance: six-sided or hexagonal-looking prism
The prism may end in a pointed termination formed by rhombohedral faces. In many amethyst geodes, the crystals are short and densely packed, so only the terminations are clearly visible.
How does amethyst form?
Amethyst forms when silica-rich fluids crystallise under suitable geological conditions. It is commonly found in cavities, fractures and veins where quartz crystals have room to grow.
Large amethyst geodes are especially associated with cavities in volcanic rocks. Mineral-rich fluids enter the cavity and deposit layers of silica along its walls. Over time, quartz crystals grow inward towards the open space.
A typical amethyst geode may contain several layers:
- an outer volcanic host rock
- a layer of agate or chalcedony
- colourless or pale quartz
- purple amethyst crystal terminations
- occasional calcite or other secondary minerals
Growth conditions, trace elements, temperature and natural irradiation all influence the final appearance of the specimen.
What forms can amethyst take?
Amethyst is available in many geological and lapidary forms.
Amethyst clusters
A cluster consists of numerous crystals growing from a shared matrix. Clusters can range from small hand-sized pieces to very large specimens.
Amethyst geodes
A geode is a hollow or partly hollow rock cavity lined with crystals. Large upright halves are sometimes sold as amethyst cathedrals.
Individual crystals
Some localities produce distinct prismatic crystals with visible sides and terminations. These may occur alone or with other minerals.
Tumbled amethyst
Tumbled stones have been rounded and polished in a rotating barrel with abrasives. They are practical as pocket stones, small gifts and introductory specimens.
Faceted amethyst
Transparent material can be cut into gemstones for rings, earrings, pendants and bracelets. Faceting is designed to improve brilliance and present the colour evenly.
Chevron amethyst
Chevron amethyst displays alternating bands of purple amethyst and white quartz. The bands often form V-shaped or zigzag patterns.
Learn more about chevron amethyst.
Ametrine
Ametrine contains both purple amethyst and yellow-to-orange citrine colour zones in the same quartz crystal. Natural ametrine is particularly associated with Bolivia.
Is chevron amethyst different from ordinary amethyst?
Chevron amethyst is not a separate mineral species. It is a patterned material made up of purple amethyst and lighter quartz growth zones.
Its striking banding makes it popular for polished freeforms, points, towers and decorative objects. Its basic hardness and composition remain those of quartz.
Where is amethyst found?
Amethyst occurs in many parts of the world. Important or well-known sources include:
- Brazil
- Uruguay
- Zambia
- Madagascar
- Namibia
- Bolivia
- Mexico
- Morocco
- Canada
- the United States
Brazilian amethyst
Brazil is a major source of amethyst geodes, clusters and commercial cutting material. Brazilian specimens vary greatly in colour, formation and size.
Uruguayan amethyst
Uruguay is known for geodes and clusters that frequently display small crystals with intense purple colour. The host rock and relatively thin agate boundary may differ visibly from many Brazilian pieces.
Zambian amethyst
Zambia is an important source of material used for faceted gemstones. Zambian amethyst can display saturated purple with bluish or reddish secondary colours.
Origin cannot be determined reliably from colour alone. Similar-looking material may come from several deposits, and a confident origin opinion may require advanced laboratory analysis.
Can amethyst change colour?
Yes. Amethyst colour can be altered by heat, prolonged intense light and irradiation.
Light exposure
Some amethyst can fade after prolonged exposure to intense sunlight or another strong light source. The degree of sensitivity varies between specimens and deposits.
To preserve its colour, avoid keeping valuable amethyst for long periods on a windowsill receiving direct sunlight.
Heat
Heating can lighten amethyst, remove its violet colour or transform it into yellow, orange, brown, green or colourless quartz, depending on the material and treatment conditions.
Many yellow-to-orange citrines in the commercial market are produced by heating amethyst. Heat-treated amethyst remains genuine quartz, but the treatment and resulting trade description should be disclosed accurately.
Irradiation
Irradiation can contribute to colour formation or alteration in quartz. Natural amethyst colour develops through naturally occurring irradiation interacting with iron-related defects. Artificial irradiation may also be used as a treatment.
Is all citrine heated amethyst?
No. Natural citrine exists, but it is comparatively uncommon. A large proportion of the citrine sold commercially is heat-treated amethyst.
Heated amethyst often displays orange, brownish orange or yellow colour. Clusters may retain white or pale bases with strongly coloured crystal tips.
Heat treatment is accepted in the gem trade when it is disclosed. It becomes misleading when heated material is marketed as untreated natural citrine.
Can amethyst be treated or synthetic?
Yes. Amethyst may be natural, laboratory-grown or treated.
Heat treatment
Heat can lighten very dark amethyst or transform suitable material into citrine-like colours.
Irradiation
Artificial irradiation may deepen or modify colour in some quartz material.
Dyeing and coating
Pale quartz, fractured quartz and lower-quality material may occasionally be dyed or coated to create or intensify purple colour.
Synthetic amethyst
Laboratory-grown amethyst has essentially the same chemical composition, crystal structure and many gemological properties as natural amethyst.
Synthetic amethyst is not glass or plastic. Distinguishing it from natural material may require microscopic examination of inclusions, twinning and growth structures by an experienced laboratory.
How can amethyst be identified?
Several observations can suggest that a specimen is amethyst, but no single home test proves its identity.
- purple colour ranging from pale violet to deep purple
- vitreous lustre
- transparent to translucent appearance
- six-sided external crystal habit
- white streak
- no cleavage
- Mohs hardness of 7
- specific gravity close to 2.65
- refractive index consistent with quartz
Why scratch testing is not recommended
A scratch test can damage the stone and may produce misleading results. Quartz, synthetic quartz and some imitations can have overlapping or similar scratch behaviour.
Can bubbles identify glass?
Rounded gas bubbles can indicate glass, but their absence does not prove that a stone is natural amethyst. Natural amethyst can contain fluid inclusions, while some glass imitations may contain few obvious bubbles.
Can colour zoning prove natural origin?
Natural-looking zoning can support an identification, but it is not conclusive on its own. Synthetic quartz can also show growth structures and colour variations.
Valuable, unusually clear or questionable stones should be examined by a qualified gemologist.
Amethyst in jewellery
With a Mohs hardness of 7 and generally good toughness, amethyst is suitable for many jewellery styles:
- pendants
- earrings
- bracelets
- necklaces
- brooches
- rings worn with appropriate care
Rings receive more knocks and abrasion than pendants or earrings. Remove an amethyst ring before exercise, gardening, cleaning or other activities that may expose it to impacts and chemicals.
Store amethyst separately from harder gemstones such as sapphire, ruby and diamond. Harder materials can scratch quartz.
Amethyst in collections and interior décor
Amethyst is popular in interiors because clusters and geodes combine strong colour with visible crystal structure.
Common decorative forms include:
- clusters
- geode halves
- amethyst cathedrals
- polished freeforms
- spheres
- towers
- carvings
- tumbled stones
Place heavy geodes and clusters on stable furniture away from the edge. Use a protective pad beneath rough bases and keep polished spheres in secure stands.
Amethyst is also frequently selected for bedrooms and evening areas because of its traditional symbolism. This is a cultural association rather than evidence that the mineral improves sleep.
Read about crystals for the bedroom.
Explore crystals for evening routines
Amethyst meaning in crystal traditions
Crystal enthusiasts traditionally associate amethyst with:
- reflection
- mental clarity
- meditation
- intuition
- balance
- a calmer atmosphere
These meanings belong to historical lore, spiritual traditions and modern crystal culture. They are separate from amethyst’s scientifically measurable mineral properties.
Amethyst has not been demonstrated to treat stress, anxiety, insomnia or another health condition. It can still be used as a meaningful object, decorative mineral or reminder connected with a personal routine.
How to clean amethyst
Warm water, a small amount of mild soap and a clean cloth or brush are generally suitable for cleaning amethyst.
- Check the specimen for loose crystals, fractures, coatings and attached minerals.
- Use warm rather than very hot water.
- Add a small amount of mild soap if necessary.
- Clean carefully without applying pressure to crystal points.
- Rinse away all soap residue.
- Dry the piece thoroughly with a clean cloth and allow crevices to air-dry.
Large clusters may contain fragile points and iron-stained matrix material. When uncertain, remove dust using a dry brush rather than soaking the specimen.
Can amethyst go in an ultrasonic cleaner?
Ultrasonic cleaning is usually considered safe for untreated amethyst without significant fractures. However, it should be avoided when:
- the stone contains fractures
- the stone has been dyed, coated or fracture filled
- its treatment history is unknown
- it is attached to a fragile matrix
- the jewellery setting is loose or delicate
Warm soapy water is the safer general method. Steam cleaning is not recommended because amethyst should not be exposed to high heat or rapid temperature changes.
How to store amethyst
- store jewellery separately from harder gemstones
- wrap faceted pieces individually
- keep clusters where their points cannot strike one another
- avoid prolonged direct sunlight
- keep the stone away from sudden temperature changes
- do not place heavy specimens on unstable shelves
- avoid contact with harsh household chemicals
Frequently asked questions about amethyst properties
What is amethyst made of?
Amethyst is silicon dioxide, SiO₂. It is the purple variety of quartz.
What is the hardness of amethyst?
Amethyst has a hardness of 7 on the Mohs scale.
Is amethyst suitable for jewellery?
Yes. Its hardness and generally good toughness make it suitable for most jewellery. Rings should still be protected from hard knocks and abrasive wear.
Does amethyst have cleavage?
No. Amethyst does not have cleavage, but it can still chip or fracture when struck.
Does amethyst fluoresce under UV light?
Amethyst is usually inert under both long-wave and short-wave UV. An unusual weak reaction may be connected with inclusions, associated minerals or treatments.
Can UV light identify natural amethyst?
No. Fluorescence is not a dependable way to distinguish natural amethyst from synthetic quartz or imitations.
What creates amethyst’s purple colour?
The colour results from iron-related defects and colour centres formed through natural irradiation within the quartz structure.
Why does amethyst have pale and dark sections?
Colour centres are often distributed unevenly during crystal growth. This creates colour zoning beneath different faces and within separate growth layers.
Can sunlight fade amethyst?
Prolonged exposure to intense sunlight can fade some amethyst. Display valuable specimens away from windows that receive strong direct light for many hours.
Can heat turn amethyst into citrine?
Suitable amethyst can turn yellow, orange or brown when heated. Much of the commercial citrine market consists of heat-treated amethyst.
Is heat-treated amethyst still genuine quartz?
Yes. Heating changes the colour but does not stop the material from being quartz. The treatment and resulting trade name should be disclosed accurately.
Is green amethyst really amethyst?
Green quartz produced from suitable amethyst is more accurately called prasiolite. “Green amethyst” is a commercial expression rather than the preferred mineralogical name.
Is chevron amethyst a separate mineral?
No. Chevron amethyst is patterned quartz containing alternating purple amethyst and lighter quartz zones.
Can natural and synthetic amethyst look identical?
Yes. Laboratory-grown amethyst can have the same composition and many of the same gemological properties as natural material. Professional microscopic examination may be required.
Where is amethyst found?
Important sources include Brazil, Uruguay, Zambia, Madagascar, Namibia, Bolivia, Mexico, Morocco, Canada and the United States.
Is amethyst the February birthstone?
Yes. Amethyst is the traditional and modern birthstone associated with February.
Can amethyst be cleaned with water?
Most untreated amethyst can be cleaned with warm water and mild soap. Avoid high heat, sudden temperature changes and harsh chemicals.
Summary
Amethyst is the purple variety of quartz. It consists of silicon dioxide, has a Mohs hardness of 7 and belongs to the trigonal crystal system.
Its colour is caused by iron-related colour centres and natural irradiation. Amethyst commonly displays uneven colour zoning and may form in geodes, clusters, veins and individual crystals.
Contrary to a common assumption, amethyst is generally inert under ultraviolet light. Fluorescence should not be used as a home test for authenticity.
Amethyst is suitable for jewellery, collecting and interior décor when protected from impacts, intense prolonged light, high heat and sudden temperature changes.