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Material World
Mineral variety · Al2O3

Sapphire

Corundum in any colour other than red — most famously blue, from iron and titanium.

Gemstone

Sapphire is gem corundum of any colour except red. Blue is the colour most people mean by the word, produced by iron and titanium together, but pink, yellow, green and colourless sapphires are all equally sapphire.

How to identify it

Sapphire is corundum, so it carries corundum's properties: hardness 9, which nothing but diamond and a few synthetics will scratch, and a density noticeably high for a transparent stone. Those two together separate it from the blue stones it is confused with — tanzanite, iolite and blue spinel are all appreciably softer.

Natural sapphire commonly shows colour banding and characteristic inclusions under magnification, where synthetic material grown from melt shows curved growth lines instead. Strong pleochroism — a shift in colour as the stone is turned — is normal in natural blue sapphire and is one of the more useful quick tests.

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

is commonly confused with

  • Ruby — mineral variety · the same mineral; only red corundum is ruby

is a component of

  • Basalt — rock · carried up as xenocrysts in alkali basalt and recovered from the gravels the basalt weathers into, rather than mined from the rock itself

is used as

contains

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 Sapphire 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

  • Sapphire → is a component of (carried up as xenocrysts in alkali basalt and recovered from the gravels the basalt weathers into, rather than mined from the rock itself) → 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
  • Sapphire → is used as (the same mineral as ruby, and the same argument for wearing it) → Jewellery and adornment
  • Sapphire → is a component of (carried up as xenocrysts in alkali basalt and recovered from the gravels the basalt weathers into, rather than mined from the rock itself) → Basalt → is used in (crushed as a premium aggregate for road base and ballast) → Construction
  • Sapphire → is a component of (carried up as xenocrysts in alkali basalt and recovered from the gravels the basalt weathers into, rather than mined from the rock itself) → 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
  • Sapphire → is a component of (carried up as xenocrysts in alkali basalt and recovered from the gravels the basalt weathers into, rather than mined from the rock itself) → 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
  • Sapphire → is a component of (carried up as xenocrysts in alkali basalt and recovered from the gravels the basalt weathers into, rather than mined from the rock itself) → 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. Sapphire ends up in others besides.