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Material World
Mineral · FeCr2O4

Chromite

Iron chromium oxide — the only ore of chromium there is, and therefore the mineral every stainless steel depends on.

Ore Refractory

Chromite is the sole ore of chromium, and chromium is what makes steel stainless. There is no second source and no substitute for the element in that role, so a material used in every kitchen and every chemical plant traces back to one mineral.

It forms early in a cooling magma and, being dense, settles out — which concentrates it into layers within large igneous intrusions. Those layered bodies are few, very large, and geographically concentrated to a degree that makes chromium one of the more strategically watched commodities.

How to identify it

Chromite is black, submetallic and weakly magnetic, and it looks a great deal like magnetite. The streak separates them: chromite gives a dark brown streak where magnetite's is black, and chromite is far less strongly magnetic.

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 an ore of

  • Chromium — element · the only commercial source of chromium, which is what makes steel stainless Wikidata

is commonly confused with

  • Magnetite — mineral · both black and submetallic; chromite's streak is dark brown against magnetite's black, and it is far less magnetic

is an input to

  • Smelting — process · reduced directly to ferrochrome; the iron in the ore is wanted rather than removed

is a component of

  • Peridotite — rock · an early-crystallising accessory that can accumulate into seams of near-pure ore — the source of essentially all the world's chromium
  • Gabbro — rock · in layered intrusions specifically, as seams that settled out of the magma early — not a feature of ordinary gabbro
  • Serpentinite — rock · relict from the peridotite, surviving the hydration that destroyed everything around it — and recovered from serpentinite for that reason
  • Refractory brick — material · in chrome-magnesite linings, and the reason spent refractory disposal is a controlled matter: chromium compounds oxidise in service to the hexavalent form

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 Chromite 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

  • Chromite → is an input to (reduced directly to ferrochrome; the iron in the ore is wanted rather than removed) → Smelting → produces (as blister copper, refined electrolytically afterwards) → Copper → is a component of → Bronze → is used to make (cast in a two-piece mould with a core, which is what bronze does better than the copper it replaced) → Bronze socketed axe → is associated with → Bronze Age complete chain
  • Chromite → is a component of (in layered intrusions specifically, as seams that settled out of the magma early — not a feature of ordinary gabbro) → Gabbro → is an input to (for the dark polished cladding and memorials sold as black granite) → 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
  • Chromite → is a component of (an early-crystallising accessory that can accumulate into seams of near-pure ore — the source of essentially all the world's chromium) → Peridotite → is a source for (partial melting of mantle peridotite is what basalt magma is — the residue left behind stays peridotite, depleted of what went into the melt) → 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
  • Chromite → is a component of (in chrome-magnesite linings, and the reason spent refractory disposal is a controlled matter: chromium compounds oxidise in service to the hexavalent form) → Refractory brick → is an input to (or installed unfired as a monolithic castable and cured by the furnace's own first heat) → Firing → produces (as sintering, from refined powders rather than clay) → Technical ceramic → is used in (the honeycomb monolith the metals are dispersed across, which supplies the surface area and survives the thermal cycling) → Catalytic converter → is used as (the largest catalytic application by metal value there is) → Catalysis
  • Chromite → is an ore of (the only commercial source of chromium, which is what makes steel stainless) → Chromium → is a component of (at least about a tenth by weight — below that the oxide film does not form) → Stainless steel → is an input to (and the heat-affected zone is where it corrodes: held between 450 and 850 °C, chromium carbides precipitate and strip the chromium from the metal beside them) → Welding → is used in (which replaced riveting during the Second World War, and taught the industry about brittle fracture in the process) → Shipbuilding
  • Chromite → is a component of (relict from the peridotite, surviving the hydration that destroyed everything around it — and recovered from serpentinite for that reason) → Serpentinite → is a source for (chrysotile is serpentine that crystallised across an opening crack, which is why it occurs as cross-fibre veins and why serpentinite hosts most of what was ever mined) → Asbestos

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