Electrum is a naturally occurring alloy of gold and silver, typically containing between 20 and 50 per cent silver alongside gold, with minor traces of copper and other elements. Its colour is a distinctive pale greenish-yellow — noticeably cooler and lighter in tone than pure or high-carat gold — and it possesses a specific gravity of approximately 15, somewhat lower than that of fine gold (19.3) owing to the lower density of its silver component. Greater hardness than pure gold made electrum practically attractive for objects subjected to wear, including coins and personal ornaments. The alloy occurs naturally in placer deposits and hydrothermal gold veins wherever gold and silver are deposited together, and it was exploited by ancient civilisations long before the metallurgical separation of the two metals was understood or attempted.

Geological occurrence

Natural electrum forms in low- to intermediate-sulphidation epithermal gold–silver deposits, as well as in alluvial placers derived from the erosion of such primary sources. The precise silver content varies considerably from deposit to deposit and even within a single deposit, reflecting local variations in the chemistry of the hydrothermal fluids from which the alloy crystallised. Notable historic sources include the river sands of the Pactolus in ancient Lydia (present-day western Turkey), the Eastern Desert of Egypt, and various localities in Nubia. Modern occurrences are documented in Nevada (United States), parts of the Witwatersrand system in South Africa, and several epithermal systems in the Pacific Rim.

Historical significance

Electrum holds a foundational place in monetary and decorative history. The Lydians, in approximately 600 BCE, are credited with striking the world's first true coins from electrum — small, bean-shaped pieces of standardised weight stamped with royal or civic devices. These staters and their fractions circulated widely across the Aegean world and are among the most historically significant objects in numismatics. The variable silver content of natural electrum, however, created problems of consistent value, and Lydian and later Greek mints progressively shifted to separately refined gold and silver coinage.

In ancient Egypt, electrum was prized for its pale, luminous colour, which was associated with the sun and with divine radiance. Obelisk tips, known as pyramidia, were sheathed in electrum to catch and reflect sunlight; the pair of obelisks erected at Karnak by Thutmose I are among the best-documented examples. Egyptian goldsmiths also used electrum for jewellery, vessels, and inlay work, sometimes sourcing it from Nubian placer deposits and sometimes producing it by deliberate alloying.

Physical and optical properties

• Composition: Gold with 20–50% silver; trace copper and other elements possible.
• Colour: Pale greenish-yellow to yellow-white, depending on silver content; higher silver yields a cooler, greener tone.
• Specific gravity: Approximately 12.5–15.5, varying with silver content.
• Hardness: Greater than pure gold; the silver component increases resistance to deformation.
• Tarnish resistance: Generally good, though slightly less resistant than fine gold owing to the silver fraction.

Electrum and modern green gold

The term electrum is occasionally applied in contemporary jewellery and metallurgical contexts to artificially formulated green-gold alloys — typically 18-carat gold alloyed with silver and sometimes cadmium or zinc to achieve a greenish hue. This usage is technically imprecise: modern green-gold alloys are deliberately engineered compositions, not naturally occurring minerals, and their silver content and trace-element profiles differ from geological electrum. The confusion is understandable given the visual similarity, but gemmological and archaeological literature reserves electrum for the natural alloy or for historically documented ancient material.

In the trade and collections

Electrum as a raw material rarely appears in the contemporary gem and jewellery trade; its primary significance is archaeological and numismatic. Ancient electrum coins and artefacts are collected as antiquities and command prices driven by historical provenance, artistic quality, and condition rather than by metal value alone. Museum collections — including those of the British Museum, the Ashmolean, and the Metropolitan Museum of Art — hold important electrum objects that remain reference points for the study of ancient metallurgy and coinage. Contemporary jewellers occasionally seek to evoke the aesthetic of ancient electrum through green-gold alloys, particularly in archaeologically inspired or historically referential pieces.