Alloy

Electrum

A natural alloy of gold and silver — what the world's first coins were struck from, and the reason coinage needed an assay from the very beginning.

Currency metal

Electrum is gold and silver mixed, and unlike almost every other alloy it occurs that way in the ground. Native gold is essentially never pure; where the silver content passes about twenty per cent the metal is pale, harder than gold and distinctly different to work, and it has its own name.

Its historical importance is out of all proportion to its use. The first coins in the world were struck from electrum in Lydia, in what is now western Turkey, in the seventh century BC — from the natural alloy carried by the river Pactolus, which is the river of the Midas story.

History

Electrum coinage created a problem that has shaped monetary systems ever since. Its gold content varies naturally from perhaps 20 to 55 per cent, and the difference is not visible — a pale coin might be worth substantially less metal than a slightly less pale one. The issuing authority knew the composition and the user did not.

That information gap is one plausible reason state coinage began at all: a stamp is a guarantee, and a guarantee is worth paying for. It is also why Croesus, a couple of generations later, moved Lydia to separate gold and silver coinages, having worked out how to part the two metals — the first bimetallic currency, and the end of electrum as money.

The assaying trades grew directly out of this. Touchstones, cupellation and eventually Archimedes' displacement method all exist to answer the question a piece of electrum poses and will not answer honestly.

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 composed of

Gold — element · 20–80% · the variable part, and the reason the alloy needed assaying: natural electrum runs anywhere from a fifth to over half gold, and the difference is not visible
Silver — element · 20–80% · the balance, which pales the colour and hardens the metal

is sourced from

Gold — element · not manufactured but mined: native gold is essentially never pure, and above about a fifth silver it is electrum and has its own name

Sources

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

Questions this page answers

Where it comes from, and what it becomes

Follow Electrum 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.

Upstream — what it comes from

Electrum → is composed of (the balance, which pales the colour and hardens the metal) → Silver → is sourced from (from the anode slimes of copper electrorefining, the same stream the platinum group and the tellurium come out of) → Copper → is produced by (as blister copper, refined electrolytically afterwards) → Smelting → takes as input (as the element removed, not added) → Oxygen → is produced by (the largest output by tonnage, and the reason air separation units sit beside steelworks) → Air separation
Electrum → is composed of (the variable part, and the reason the alloy needed assaying: natural electrum runs anywhere from a fifth to over half gold, and the difference is not visible) → Gold → is sourced from (a significant share of world gold arrives this way, recovered from copper anode slimes at no mining cost of its own) → Copper → is produced by (as blister copper, refined electrolytically afterwards) → Smelting → takes as input (as the element removed, not added) → Oxygen → is produced by (the largest output by tonnage, and the reason air separation units sit beside steelworks) → Air separation
Electrum → is composed of (the balance, which pales the colour and hardens the metal) → Silver → is sourced from (from the anode slimes of copper electrorefining, the same stream the platinum group and the tellurium come out of) → Copper → is extracted from (the principal copper ore worldwide) → Chalcopyrite
Electrum → is composed of (the variable part, and the reason the alloy needed assaying: natural electrum runs anywhere from a fifth to over half gold, and the difference is not visible) → Gold → is sourced from (a significant share of world gold arrives this way, recovered from copper anode slimes at no mining cost of its own) → Copper → is extracted from (the principal copper ore worldwide) → Chalcopyrite
Electrum → is composed of (the balance, which pales the colour and hardens the metal) → Silver → is sourced from (from the anode slimes of copper electrorefining, the same stream the platinum group and the tellurium come out of) → Copper → is produced by (as blister copper, refined electrolytically afterwards) → Smelting → takes as input (roasted to drive off sulfur, then reduced to copper) → Chalcopyrite
Electrum → is composed of (the balance, which pales the colour and hardens the metal) → Silver → is sourced from (from the anode slimes of copper electrorefining, the same stream the platinum group and the tellurium come out of) → Copper → is produced by (as blister copper, refined electrolytically afterwards) → Smelting → takes as input (reduced with carbon to metallic tin) → Cassiterite

These are the most distinct paths back. Electrum can be traced through others besides.