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Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. It is the hardest known natural material on the Mohs scale of mineral hardness (10). This extreme hardness, combined with its high refractive index and dispersion, gives polished diamonds their characteristic brilliance and 'fire'. Diamonds are typically colorless, but impurities can result in various colors, including yellow, brown, green, blue, pink, red, and black. They are chemically inert and excellent electrical insulators, but good thermal conductors.
How to Identify
- Color
- Typically colorless to pale yellow or brown, but can occur in nearly any color (fancy colors) due to impurities or structural defects. Common colors include yellow, brown, green, blue, pink, red, and black.
- Luster
- Adamantine (diamond-like), exceptionally bright and reflective.
- Texture
- Rough, often greasy or waxy on unpolished surfaces; polished surfaces are extremely smooth.
- Crystal Form
- Cubic system, commonly found as octahedra, dodecahedra, cubes, or combinations thereof. Macles (twinned crystals) are also common. Often exhibits trigons (triangular growth marks) on octahedral faces.
- Cleavage
- Perfect octahedral cleavage in four directions. This means it can be split along specific planes, despite its extreme hardness.
- Geological Environment
- Primarily found in kimberlite and lamproite pipes (volcanic conduits) that originate in the Earth's mantle. Also found in alluvial (placer) deposits, which are secondary deposits formed by the erosion and transport of primary kimberlite/lamproite sources.
Key Facts
- Hardness: 10 (Mohs scale), the hardest natural mineral.
- Specific Gravity: 3.50 - 3.53 g/cm³ (varies slightly with impurities).
- Crystal System: Cubic (isometric).
- Color: Colorless, yellow, brown, green, blue, pink, red, black, and other fancy colors.
- Luster: Adamantine.
- Transparency: Transparent to opaque.
- Fracture: Conchoidal to uneven.
- Cleavage: Perfect octahedral in four directions.
- Composition: Pure carbon (C).
Quick Check
- Color: Colorless to yellow/brown, but can be any color.
- Luster: Adamantine (brilliant, glassy).
- Streak: Colorless (as it is pure carbon and harder than the streak plate).
Physical Characteristics
- Crystal Habit: Octahedral, dodecahedral, cubic, or combinations; often rounded or distorted; also massive (bort) or radiating (carbonado).
- Cleavage Type: Perfect, octahedral {111}.
- Fracture Type: Conchoidal to uneven.
- Tenacity: Brittle (despite extreme hardness, it can be fractured or cleaved by impact).
- Luster Type: Adamantine.
Formation
Diamonds form under extreme conditions of high pressure and high temperature deep within the Earth's mantle, typically at depths of 140 to 190 kilometers (87 to 118 miles). The required temperature range is approximately 900 to 1,300 degrees Celsius (1,652 to 2,372 degrees Fahrenheit). These conditions are found within the stable continental lithosphere, specifically in cratons. Diamonds are brought to the Earth's surface through deep-seated volcanic eruptions, primarily by kimberlite and lamproite magmas, which ascend rapidly, preventing the diamonds from reverting to graphite.
Usage
Diamonds are highly valued as gemstones for jewelry due to their exceptional brilliance, fire, and hardness. Industrially, their extreme hardness makes them indispensable for cutting, grinding, drilling, and polishing tools. They are used in abrasive powders, drill bits, saw blades, and in high-precision machining. Synthetic diamonds are also produced for these industrial applications and increasingly for technological uses such as heat sinks in electronics and in quantum computing research.
Age Distribution
Diamonds range in age from approximately 990 million years to over 4.2 billion years, with most commercial diamonds being between 1 billion and 3.5 billion years old. They are among the oldest materials on Earth.
Where to Find
Botswana
World's leading producer by value, with major mines like Orapa, Jwaneng, and Damtshaa, primarily from kimberlite pipes.
Russia
Largest producer by volume, particularly in Siberia (Yakutia), with significant kimberlite pipe deposits such as Mir and Udachnaya.
Canada
Significant producer from kimberlite pipes in the Northwest Territories (e.g., Ekati, Diavik, Gahcho Kué) and Nunavut.
Australia
Historically a major producer, especially of fancy pink and red diamonds from the Argyle mine (now closed), primarily from lamproite pipes. Also produces industrial diamonds.
South Africa
Historically the first major source of diamonds, with famous mines like Kimberley (Big Hole) and Cullinan (Premier Mine), primarily from kimberlite pipes.
Angola
Significant producer from both kimberlite pipes and extensive alluvial deposits.
Finding Tips
Primary Deposits (Kimberlite/Lamproite Pipes)
Diamonds are found within these igneous rocks. Prospecting involves identifying these specific rock types, often through geophysical surveys and indicator mineral sampling (e.g., pyrope garnet, ilmenite, chromite).
Secondary Deposits (Alluvial/Placer)
Diamonds, being dense and resistant to weathering, accumulate in riverbeds, ancient river channels, and coastal areas. Look for gravels and conglomerates in areas downstream from known or suspected primary sources. Panning and sluicing are common recovery methods.
Indicator Minerals
Geologists often search for 'indicator minerals' that are commonly found alongside diamonds in kimberlite and lamproite, such as distinctive varieties of garnet (pyrope), ilmenite, chromite, and clinopyroxene. These minerals are more abundant and easier to find than diamonds themselves.
Safety Precautions
Diamond prospecting, especially in primary deposits, often involves large-scale mining operations that are not accessible to the public. Alluvial prospecting may occur in remote or environmentally sensitive areas. Always obtain necessary permits and adhere to local regulations. Be aware of potential hazards in mining environments.
Similar Rocks
Moissanite
Moissanite
Also known as: Silicon Carbide
Cubic Zirconia
Zirconium Dioxide (stabilized)
Also known as: CZ
White Sapphire
Corundum
Also known as: Colorless Corundum
Topaz
Topaz
Also known as: Aluminum Silicate Fluoride Hydroxide
Scientific Classification
- Mineral Class
- Native Elements
- Group
- Carbon Group
- Crystal System
- Cubic (Isometric)
- Chemical Formula
- C
- Composition
- Pure carbon
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