Native elements represent a small but significant group of minerals that have formed in a pure, uncombined state in the Earth’s crust. Unlike the vast majority of minerals, which are chemical compounds made of two or more elements bonded together, native elements consist of atoms of a single element. This means they possess the same chemical formula as the element itself. Their rarity in this pure form makes them noteworthy in mineralogy.
The Defining Characteristics of Native Elements
A substance is classified as a native element mineral only if its structure is made up of a single type of atom. For instance, native gold is composed exclusively of gold atoms (Au), while a common mineral like halite (NaCl) is a compound of sodium and chlorine. This singular atomic composition fundamentally separates native elements from the thousands of other mineral species.
The uncombined nature of these elements often results from their low chemical reactivity, allowing them to remain isolated in geological environments. Elements like gold and platinum are chemically inert, meaning they resist bonding with oxygen or other active elements. This preserves their native state, where the mineral’s crystal structure is built entirely from a repeating pattern of its own atoms. Native elements are formally recognized as one of the major classes within the broader mineral classification system.
Their physical properties are a direct result of the atomic bonding within this pure structure. Metallic native elements, such as copper, are characterized by metallic bonding, where a sea of delocalized electrons allows for high electrical and thermal conductivity. Conversely, native non-metals like sulfur exhibit covalent bonding, leading to different characteristics like a distinct odor and a low melting point.
Major Classes and Common Examples
Native elements are grouped into three classes based on their chemical and physical properties: metals, semi-metals, and non-metals. The native metals group is the most well-known and includes the coinage metals—gold, silver, and copper—along with the platinum group elements. Gold (Au) is prized for its intense yellow color, high density, and extreme malleability. Silver (Ag) and copper (Cu) are excellent conductors of heat and electricity, with copper often found in the form of branching wires or plates.
The native semi-metals, sometimes referred to as metalloids, include elements such as arsenic (As), antimony (Sb), and bismuth (Bi). These elements possess properties that fall between those of true metals and non-metals. They are typically brittle and are less effective at conducting heat and electricity compared to the native metals. Native antimony, when fresh, displays a metallic luster but quickly tarnishes to a dull gray color.
The third class is the native non-metals, which are dominated by carbon and sulfur. Native carbon exists in two dramatically different forms, or polymorphs: diamond and graphite. Diamond forms under immense pressure deep within the Earth and is the hardest known natural substance, featuring a tightly-packed three-dimensional crystal structure. Graphite forms under less extreme conditions, featuring a layered structure that gives it a soft, slippery texture, making it an effective lubricant. Sulfur (S) is also a significant native non-metal, recognized for its bright yellow color and low specific gravity.
Geological Formation and Occurrence
The formation of native elements requires specific geological conditions that prevent the element from chemically bonding with others. One primary mechanism is hydrothermal deposition, where hot, mineral-rich water circulates through the Earth’s crust. These fluids dissolve elements and then deposit them as pure metal in veins and fractures as the fluid cools or reacts with the surrounding rock. This process is a major source for native gold, silver, and copper deposits.
Another important process is magmatic crystallization, which occurs within cooling magma deep underground. Elements like the platinum group metals often crystallize early from the molten rock, concentrating in layers within certain igneous intrusions. Native iron, while rare on Earth’s surface, is found in basalts and often associated with meteorites.
Reduction processes are also responsible for the formation of certain native elements, particularly non-metals and semi-metals. Native sulfur, for instance, often forms in sedimentary rocks overlying salt domes, where bacteria reduce sulfate minerals like gypsum, or near volcanic vents where hydrogen sulfide gas is oxidized. Diamond is formed under extremely high pressure and temperature deep in the mantle and is brought to the surface through rare, pipe-like volcanic intrusions called kimberlites. After the initial formation, physical processes like weathering can erode primary deposits and concentrate dense native metals like gold and platinum into placer deposits in riverbeds.