Most metals in the Earth’s crust are chemically bound to other elements, such as oxygen or sulfur, forming stable compounds known as ores. A native metal is an exception, representing elements that occur naturally in their uncombined, metallic form. This occurrence results from specific geological conditions and the inherent chemical properties of the metal itself.
The Definition of a Native Metal
A native metal is defined as any metal found in nature as a simple, uncombined element, not bonded into a mineral compound. For a metal to exist in this elemental state over geological timescales, it must possess a high degree of chemical inertness.
Highly reactive metals, such as iron, oxidize readily, forming stable compounds like iron oxide (rust) when exposed to oxygen and water. Only metals with a low chemical affinity for other elements, particularly oxygen and sulfur, can resist this natural weathering and corrosion process. Their position below hydrogen on the electrochemical series indicates this low reactivity, allowing them to remain in their metallic state within the Earth’s crust.
Prominent Examples Found in Nature
The most common native metals are gold, silver, and copper, alongside the Platinum Group Metals (PGMs), which include platinum, palladium, and iridium. Native gold is the most stable and common, predominantly found as flakes, fine grains, or larger masses known as nuggets. Because gold is exceptionally resistant to chemical attack, the majority of the metal mined globally is in this pure, native form.
Native silver is less common than gold because it is slightly more reactive, often occurring alloyed with gold as electrum or with sulfur in sulfide minerals. When pure, it typically appears as irregular masses, thin sheets, or wire-like dendritic coatings. Copper is also a native metal, sometimes discovered in massive deposits, with individual masses weighing hundreds of tons. The Platinum Group Metals are usually found as native alloys, appearing as small, dense grains associated with ultramafic igneous rocks.
Geological Processes of Formation
The formation of native metal deposits requires geological environments that either prevent chemical bonding or actively reduce existing compounds back into a pure metal. Deposits are categorized into two mechanisms: primary and secondary. Primary deposits form deep within the Earth, often associated with hydrothermal processes near cooling magma chambers.
In these environments, superheated, chemically active fluids circulate through the rock, dissolving and transporting metal ions. As these metal-rich fluids move into cooler zones or encounter rocks that change the fluid’s chemistry, the dissolved metals precipitate out. Native gold is frequently deposited in quartz veins as the fluid cools and the pressure drops.
Secondary, or supergene, deposits form closer to the Earth’s surface through the weathering of primary ore bodies. This process involves chemical reduction, where a metal-bearing compound, such as a copper sulfide, is broken down by near-surface water and oxygen. The metal ions are chemically reduced back to their elemental state, resulting in native copper that can form large masses within the weathered zone.
Early Human Use and Significance
The discovery of native metals was transformative because these materials required no complex processing. They could be used immediately without the need for smelting, the high-heat process required to extract metal from an ore. This accessibility made native gold, silver, and copper the first metals utilized by early civilizations.
Native metals were used primarily for ornamentation due to their attractive luster and malleability, especially gold and silver. Copper, while soft, could be repeatedly hammered (cold-working) to achieve a harder edge suitable for simple tools and weapons. The widespread use of naturally occurring copper deposits marked the beginning of the Chalcolithic period, or Copper Age, which preceded the Bronze Age.