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Material World
Mineral variety · SiO2

Amethyst

The purple variety of quartz, coloured by iron impurities and natural irradiation.

Gemstone Collectible specimen

Amethyst is quartz, chemically and structurally identical to the colourless mineral, made purple by iron impurities that have been altered by natural radiation in the ground. Heating it drives the colour toward yellow-brown, which is how much commercial citrine is produced.

It is a variety, not a species. That distinction matters: everything true of quartz's hardness, structure and chemistry is true of amethyst, and treating it as a separate mineral would mean maintaining two copies of the same facts.

Name origin

From Greek amethystos, 'not intoxicated' — from a belief that the stone protected its wearer from drunkenness, which is why ancient drinking vessels were sometimes made from it.

How to identify it

Purple quartz, with quartz's hardness of 7 and conchoidal fracture. The colour is often unevenly distributed in bands or patches following the crystal's growth zones, which is a useful sign of natural origin: uniformly coloured material is more likely to have been treated.

Medium confidence Weak evidence

How we know: checked recently · only one source, so there is nothing to cross-check it against · stated directly by the source.

How this connects

Where a connection has been confirmed by an outside reference, that reference is named beside it.

is a variety of

contains

is a component of

  • Basalt — rock · lining vugs and geodes in weathered basalt flows, which is where nearly all of the world's amethyst comes from — the cavity is a gas bubble the lava left behind

is commonly confused with

  • Citrine — mineral variety · the same mineral with the same iron in different oxidation states, and heating turns one into the other — which is where most commercial citrine comes from

is used as

  • Jewellery and adornment — application · the commonest good gemstone there is, and worth a fraction of what it was before Brazilian supply arrived in the 1800s

Sources

  • Material World
    Our own writing
  • Wikidata
    Wikimedia Foundation · Creative Commons CC0 1.0 Universal (public domain dedication)

Questions this page answers

Where it comes from, and what it becomes

Follow Amethyst back to what it starts as, and forward into what it becomes. Each step is a documented one — a real route material takes, not a chain of inference.

Downstream — what it becomes

  • Amethyst → is a component of (lining vugs and geodes in weathered basalt flows, which is where nearly all of the world's amethyst comes from — the cavity is a gas bubble the lava left behind) → Basalt → is an input to (for aggregate rather than dimension stone — hard, tough and angular, which is what a road base needs) → Quarrying → produces (cut rather than blasted, because a quarry that shatters its stone has destroyed what it came for) → Dimension stone → is used in (quarried rather than mined, and the distinction is legal and technical rather than merely a word) → Mining and quarrying → is associated with (steam pumping allowed mines below the water table, which is what made deep coal possible) → Industrial Revolution complete chain
  • Amethyst → is used as (the commonest good gemstone there is, and worth a fraction of what it was before Brazilian supply arrived in the 1800s) → Jewellery and adornment
  • Amethyst → is a component of (lining vugs and geodes in weathered basalt flows, which is where nearly all of the world's amethyst comes from — the cavity is a gas bubble the lava left behind) → Basalt → is used in (crushed as a premium aggregate for road base and ballast) → Construction
  • Amethyst → is a component of (lining vugs and geodes in weathered basalt flows, which is where nearly all of the world's amethyst comes from — the cavity is a gas bubble the lava left behind) → Basalt → is an input to (for aggregate rather than dimension stone — hard, tough and angular, which is what a road base needs) → Quarrying → produces (crushed and graded from quarried rock, and the grading is the product — a concrete mix specifies a size distribution, not a stone) → Aggregate → is a component of (95 per cent of it by mass — the stone carries the load and the bitumen keeps the water out) → Asphalt concrete → is used as (as pavement rather than as structure: a surface that spreads a wheel load into the ground beneath it) → Structural engineering
  • Amethyst → is a component of (lining vugs and geodes in weathered basalt flows, which is where nearly all of the world's amethyst comes from — the cavity is a gas bubble the lava left behind) → Basalt → is an input to (for aggregate rather than dimension stone — hard, tough and angular, which is what a road base needs) → Quarrying → produces (crushed and graded from quarried rock, and the grading is the product — a concrete mix specifies a size distribution, not a stone) → Aggregate → is a component of (70 to 80 per cent by volume — the cement is the expensive part and the stone is most of the material) → Concrete → is used in (foundations, frames, floors and civil structures) → Construction
  • Amethyst → is a component of (lining vugs and geodes in weathered basalt flows, which is where nearly all of the world's amethyst comes from — the cavity is a gas bubble the lava left behind) → Basalt → is an input to (for aggregate rather than dimension stone — hard, tough and angular, which is what a road base needs) → Quarrying → produces (cut rather than blasted, because a quarry that shatters its stone has destroyed what it came for) → Dimension stone → is used in (cladding, flooring, kerbs and monuments) → Construction

These are the most distinct paths onward. Amethyst ends up in others besides.