Introduction to Native Elements

What are Native Elements?

Native element minerals are defined as single-element minerals or naturally occurring metallic alloys. Of the 118 known elements featured on the periodic table, only 19 can occur naturally in a native form. This means they can create a crystal structure without combining with other elements.

Native elements share some characteristics (with exceptions, of course). All native elements are chemically inert or non-reactive. This allows them to create minerals with only one type of atom. The most well-known native elements are gold (Au), silver (Ag), diamond (C), and sulfur (S). 

Historically, native element minerals were the first metals to be worked and mined. Only later did people develop refining techniques for extracting elements from more complex minerals. (Chemically, that means breaking bonds between two or more different atoms to get to one type of atom).

The Native Elements Mineral Class

The native elements mineral class can be divided into three groups:

• Metals 
• Semimetals
• Nonmetals

Metals

The native elements metals group is itself divided into three sub-groups:

• Gold sub-group
• Platinum sub-group 
• Iron sub-group

Gold Sub-Group

The gold sub-group includes not only gold but also silver, copper (Cu), and lead (Pb). These elements share many characteristics.

All members of the gold sub-group have a cubic close-packed structure (CCP), a very rare type of atomic packing arrangement. Metallic bonding connects all the same-sized ions or atoms very tightly. This CCP structure determines most of this subgroup's physical and chemical properties characteristics.

ADD PIC - Gold unit, an example of a CCP Structure

Since CCP structure is highly symmetrical, the physical and chemical properties of gold sub-group crystals are identical in any direction. These crystals form in the isometric system and have cubic symmetry. All gold sub-group members conduct heat and electricity well and have high densities. They are also soft, malleable, ductile, and sectile.

Visually, we can observe that gold sub-group members combine metallic lusters with various outstanding colors (orangey-yellow for gold, gray for silver and lead, and orange-brown for copper). These metals also have hackly (hook-shaped) fractures. If you hold a sample of one of these metals in your hand, you can appreciate its density. It will feel heavier than you might assume for a sample of its size.

Despite their similarities, the minerals in the gold sub-group have some differences, especially in color and density.

Gold

Gold is very malleable and ductile. It also resists corrosion. Thus, it's widely used for jewelry. Like all native elements, gold is chemically inert. Therefore, gold occurs naturally as a pure metal in nugget form. However, since gold's atomic radius is very similar to silver's, gold almost always occurs naturally in alloys with silver. (Naturally occurring metallic alloys are still considered native elements).

Gold has another surprising property. It conducts electricity better than copper. Most quality electrical wires are made from copper. (Just imagine golden cables at home and all over the world conducting electricity!)

Silver

Silver occurs naturally in wire-like or arborescent (tree-like) forms or massive forms in hydrothermal veins. Since silver is less inert chemically than gold, it tarnishes easily, reacting with oxygen in the atmosphere and creating an oxide film on its surface. You can see this as a black tarnish with a dull or earthy luster.

Copper

Copper occurs naturally as branching sheets, plates, wires, and massive pieces. Copper's most distinguishing characteristic is its orange-brown color. Like silver, copper can have oxides or carbonates (patinas) on its surface. However, these have a green color.

Lead

Native lead is even rarer than copper. It usually occurs as a sulfide rather than a native element. In a fresh, unoxidized state, lead's color ranges from light gray to slightly blueish gray. Native lead mineral specimens lack metallic luster.

Platinum Sub-Group

The platinum sub-group of native elements — also known as platinoids or platinum-group elements (PGEs) — consists of six elements with similar properties. They are ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), and platinum (Pt).

Minerals of the platinum sub-group are harder and have higher melting points than those of the gold sub-group. (For example, osmium has a melting point of 3,033° C; gold has a melting point of 1,064° C). Platinum native elements also have high densities. (For example, platinum has a density of 22 g/cm³; gold has a density of 19.3 g/cm³). All platinum sub-group members have very similar atomic radii, which makes substitutions for alloy formation relatively easy. As a result, these native elements never occur in pure form.

Platinum

The primary sources of platinum are ultramafic and mafic igneous rocks. Native platinum is much rarer than gold sub-group native elements. Platinum is commonly produced commercially as a by-product of nickel and copper ore processing. Like gold, platinum has a high resistance to tarnishing and other chemical degradation. Thus, in addition to jewelry use, it has many practical uses.

Iron Sub-Group

The iron sub-group of native elements consists of iron (Fe), nickel (Ni), and their alloys.

You will rarely find iron in its native form on the Earth's surface. Iron is more chemically reactive than any of the metals covered so far. Iron tends to combine with oxygen or sulfur. Iron-nickel alloys are found primarily in meteorites because forming native iron and nickel requires an exceptionally oxygen-starved environment, such as outer space. According to one theory, the Earth's core consists of iron alloys, and its movement creates our planet's magnetic field. (See Birch, 1952, and Antonangeli et al., 2010)

Semimetals

Semimetals are elements with properties between those of metals and solid nonmetals. Examples of semimetals include arsenic (As), bismuth (Bi), and antimony (Sb). Semimetal properties differ from those of the metal group of native elements. In nature, semimetals also occur quite rarely in pure forms. Beautiful, skeletal bismuth crystals with iridescent, rainbow-like surfaces popular at mineral shows are synthetics.

Atoms in covalent compounds like semimetals are bonded via covalent bonds rather than metallic ones. This brings some atoms closer together than others, which results in a less symmetrical structure. Consequently, covalent compounds have some physical properties that differ in different directions.

Covalent bonding results in atomic weaknesses in crystal structures and, thus, creates good cleavage. ("Good" cleavage means the crystals can split along internal planes more easily). Semimetal minerals are also brittle and have lower heat and electrical conductivity than metal group native elements.

Nonmetals

The nonmetal group includes sulfur (S) and two well-known polymorphic modifications of carbon (C): graphite and diamond.

The properties of nonmetal native elements differ significantly from those of the metal and semimetal groups. Nonmetals don't have metallic lusters. For example, diamond has an adamantine or "diamond-like" luster, and sulfur's luster can appear vitreous ("glass-like"), resinous, or greasy. Covalent bonds also make nonmetals brittle instead of ductile.

Sulfur

Sulfur forms as a bright yellow native mineral in the orthorhombic crystal system. (Monoclinic sulfur-β and rosickýite are polymorphic modifications of sulfur). Sulfur frequently occurs in its native crystal state, especially near volcanic activity and fumarole regions. These crystals have a very low hardness of 1.5-2.5 and extreme sensitivity to temperature. They have a low melting point of 112° С. Sulfur has a very unpleasant smell, so handle it with care.

Diamond and Graphite

Diamond and graphite are polymorphs. This means they have the same chemical composition but different atomic arrangements. Both are made of carbon atoms, but diamond has an isometric crystal structure, while graphite has a hexagonal crystal structure. These different atomic arrangements result in dramatically different physical properties.

Carbon Atomic Arrangements

In diamonds, carbon atoms are covalently bonded into tetrahedra, connected into an overall cubic arrangement with the same properties in all directions. However, the crystal has internal planes where the atomic bonds are weak. This gives diamonds perfect cleavage along the octahedral plane. (Crystals with "perfect" cleavage are the easiest to split).

In graphite, carbon atoms are covalently bonded into rings made of six carbon atoms. These carbon rings combine into layers held together by very weak van der Waals forces. The distance between these layers results in perfect cleavage.

Physical Differences Between Diamond and Graphite

Although diamond and graphite both have perfect cleavage, their hardness differs significantly. Diamond's tetrahedral atomic arrangement makes it very resistant to scratching. In fact, diamond has the highest score on the Mohs scale of hardness of any natural material, a 10. On the other hand, graphite's weakly bound hexagonal layers make it very easy to scratch. Graphite has the lowest score on the Mohs scale, a 1. This property makes graphite well-suited for pencils. Writing with a graphite pencil removes layers of graphite by applying force to the pencil. Popular "Number 2" pencils actually combine clay with graphite to increase the hardness of the writing tip.

Diamond and graphite also differ in electrical conductivity due to their atomic structure. Diamonds don't conduct electricity. (A moissanite tester measures electroconductivity and can thus distinguish diamonds from moissanite lookalikes). In contrast, graphites make good conductors.

How Do Diamond and Graphite Form?

Depending on the underground formation environment, carbon sometimes forms diamond and sometimes graphite. Graphite commonly occurs in many metamorphic rocks (marbles, schists, and gneisses). The carbon in graphite typically originates from organic material in the original sediments. The pressure applied to this organic carbon creates graphite.

Diamond formation requires very different pressure and temperature conditions. Diamonds form only at very high pressures associated with Earth's lowermost crust or mantle.

Diagnostic Characteristics of Common Native Elements

Below, you'll find the diagnostic characteristics of the most common native element minerals. The best diagnostic characteristics of each element are highlighted in bold. These will help you differentiate them from similar-looking minerals.

Gold Properties

Gold can be mistaken for pyrite (sometimes called fool's gold) and chalcopyrite. However, pyrite and chalcopyrite have significantly lower density (4.8-5 and 4.1-4.3, respectively) and greater hardness (6-6.5 and 3.5-4, respectively) than gold. Gold also has a yellow streak, while pyrite and chalcopyrite have greenish black streaks.

Silver Properties

Silver can be mistaken for platinum and various other gray sulfides. Platinum has a much higher density than silver. Unlike sulfides, silver will also have some dull, tarnished, dark gray areas.

Copper Properties

Copper's typical pinkish color tone makes identifying it relatively straightforward..

Platinum Properties

Platinum's density exceeds that of any other native metal.

Sulfur Properties

Sulfur's typically vibrant yellow color makes it relatively easy to identify. Carnotite, a uranium-bearing mineral, can sometimes be mistaken for sulfur. However, carnotite has a greater density (4.70) than sulfur. It's also much rarer and radioactive.

Graphite Properties

Graphite is so soft it will shed tiny gray flakes if handled. Molybdenite can sometimes be mistaken for graphite because it also has a metallic, silver blueish color and low hardness (1-1.5). However, molybdenite has a greater density (4.62-4.73) than graphite and will feel heavier in your hand..

Diamond Properties

Diamond is the hardest mineral. It can scratch any other mineral, and only diamonds can scratch other diamonds. Rough diamond crystals have an octahedral habit rarely seen in other transparent and colorless minerals.

References for Native Elements

1. Antonangeli, D., et al.. "Composition of the Earth's inner core from high-pressure sound velocity measurements in Fe-Ni-Si alloys." Earth and Planetary Science Letters, 295(1-2), pp. 292-296. (2010). (Accessed 10/20/24)
2. Anthony, B. J. & Bideaux, R. A. "Handbook of Mineralogy: Volume I, Elements." American Mineralogist, 77, 1122. (1992).
3. Birch F. "Elasticity and constitution of the Earth's interior." J. Geophys. Res. 57, 227- 286. (1952).
4. Jiang, Q., et al.. "The size dependence of the diamond-graphite transition." Journal of Physics: Condensed Matter, 12(26), 5623, (2000). (Accessed 10/20/24)
5. Klein, C. & Dutrow, B. Manual of Mineral Science. John Wiley & Sons. (2007).

Olena Rybnikova, PhD

Olena Rybnikova is a gemologist and mineralogist. She has a PhD in mineralogy and petrology specializing in beryllium minerals and is a certified Applied Jewelry Professional accredited by the Gemological Institute of America. Her passion is actively promoting knowledge and appreciation of nature, geology, and gemstones.

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