Gem library
Smoky quartz
Quartz the colour of smoke and whisky
Smoky quartz owes its brown colour to natural irradiation that displaced electrons around aluminium atoms trapped in the lattice. It is a crystal of the granitic basement — sober, very affordable, and one of the few genuinely transparent dark quartzes.
- Hardness (Mohs)
- 7
- Density
- 2.65
- Crystal system
- Trigonal
- Refractive index
- 1.544 – 1.553
- Cleavage
- None
Mineralogical identity
- Family
- Quartz — silica group
- Species
- Quartz
- Variety
- Smoky quartz (morion when black)
- Chemical formula
- SiO₂
- Crystal system
- Trigonal (rhombohedral)
- Classification
- Semi-precious stone
- Rarity
- Very common
- Indicative price
- €1 – 12/ct
Etymology
Descriptive: the colour evokes smoke. Opaque black quartz is called morion, and the Scottish variety is cairngorm, after the Cairngorm mountains.
Physical & optical properties
- Hardness (Mohs)
- 7
- Density
- 2.65
- Refractive index
- 1.544 – 1.553
- Birefringence
- 0.009
- Cleavage
- None
- Fracture
- Conchoidal
- Lustre
- Vitreous
- Diaphaneity
- Transparent to translucent
- UV fluorescence
- None
- Pleochroism
- Weak
- Colours
- brown, grey, smoky black
Formation, geology & history
A colour born of radioactivity
The brown of smoky quartz comes not from a pigment but from a colour centre: natural radiation emitted by potassium-40 and uranium in nearby granite strips an electron from an aluminium atom substituted for silicon. The resulting defect absorbs part of the visible spectrum and produces the smoky tint. The longer the irradiation, the darker the stone, up to almost-black morion. This mechanism also explains why smoky quartz decolourises with heat: heating to 300-400 °C restores the missing electron and turns the stone colourless, or sometimes yellow (citrine).
Natural or irradiated?
The market contains many colourless quartzes irradiated artificially to obtain a deep, sometimes near-black brown. The result is stable but the tone is often too uniform and slightly greyish, without the soft zoning of natural stones. Alpine fissure crystals, often pale grey-brown with marked zoning and chlorite inclusions, are a mark of natural origin. In practice the distinction has little effect on value, which is very low either way.
Uses and varieties
Its transparency and available size make it a favourite for large costume-jewellery gems and contemporary fantasy cuts. Golden-brown Scottish cairngorm traditionally adorns Highland brooches and dirk handles. Smoky quartz also serves as an optical material: the first sunglass lenses were cut from natural smoky quartz plates, which filter part of the radiation without distorting colours.
How to recognise it
- Brown transparency, even in depthTrue smoky quartz transmits light even when dark, with soft zoning. A completely opaque black is more likely obsidian or glass.
- Prism striationsOn natural points, the horizontal striations of the prism faces mark it as quartz.
- Hardness and coolnessIt scratches glass, stays cool to the touch and rings clear: three markers dyed glass cannot reproduce.
Imitations, treatments & confusions
- Smoked glassVery common in beads: bubbles, seams, immediate warmth, and above all no birefringence on a fine line.
- ObsidianNot a counterfeit but a frequent confusion: obsidian is an opaque volcanic glass, hardness 5, with a very sharp fracture and greasy lustre.
- Irradiated colourless quartzA legal treatment that must be declared. The tone is too flat, often grey-brown without nuance, with no natural inclusions.
Deposits & origins
Brazil, Switzerland and the French Alps (fissure crystals), Madagascar, Scotland (cairngorm, the national stone worn on the kilt), Ukraine, Namibia, Colorado (USA)
Care & precautions
- Warm soapy water, soft brush: no particular constraint.
- Avoid heat: above 200 °C the brown colour disappears permanently.
- Intense sunlight eventually lightens the tone; prefer a shaded display case.
- Resistant to ultrasonic cleaning except on fractured or heavily included pieces.
Traditions & crystal healing
- Chakras
- Root · solar plexus
- Zodiac signs
- Capricorn · Scorpio
- Element
- Earth
Tradition links it to grounding: it is said to help you find the floor under your feet again, get through stressful spells and disperse rumination. It is often presented as the earthly counterpart of amethyst — more concrete, more protective, recommended to anxious temperaments.
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
Is smoky quartz radioactive?
No, not at all. The irradiation that coloured it, natural or artificial, leaves no residual radioactivity: it merely displaced electrons in the crystal lattice.
Smoky quartz or morion?
Morion is simply smoky quartz so dark that it becomes nearly opaque. Same mineral, same formula; only the intensity of irradiation differs.
Can it become citrine?
Yes: heated to around 400 °C, some iron-rich smoky quartzes turn golden yellow. It is one source of commercial citrine, alongside heated amethyst.