Diamond

Description

Diamond is a metastable allotrope of carbon, where carbon atoms are arranged in a crystal structure called diamond cubic. It is the hardest known natural material and possesses exceptional thermal conductivity, high electrical resistivity, and a high refractive index. Its unique combination of physical properties makes it invaluable for both ornamental and industrial purposes. While commonly associated with colorless transparency, diamonds can occur in a range of colors due to impurities or structural defects.

How to Identify

Color

Colorless, yellow, brown, green, blue, pink, red, orange, black. The most prized are colorless, but fancy colors are also highly valued.

Luster

Adamantine (brilliant, diamond-like).

Texture

Smooth to slightly rough on natural crystal faces; fractured surfaces are conchoidal.

Crystal Form

Typically octahedral, dodecahedral, or cubic. Often found as euhedral crystals, but also as irregular fragments or bort (industrial-grade diamonds with poor crystal structure).

Cleavage

Perfect in four directions (octahedral), which can be exploited for cutting but also makes them susceptible to fracture along these planes.

Geological Environment

Primary deposits are kimberlite and lamproite pipes. Secondary (alluvial) deposits are found in riverbeds and coastal areas where diamonds have been eroded from their primary sources and transported.

Key Facts

• Hardness: 10 (Mohs scale), the hardest known natural mineral.
• Specific Gravity: 3.50 - 3.53 g/cm³ (varies slightly with impurities).
• Crystal System: Isometric (cubic).
• Color: Colorless, yellow, brown, green, blue, pink, red, orange, black. Can be transparent, translucent, or opaque.
• Luster: Adamantine.
• Transparency: Transparent to opaque.
• Fracture: Conchoidal to uneven.
• Cleavage: Perfect in four directions (octahedral).
• Composition: Pure carbon (C).

Quick Check

• Color: Variable (colorless, yellow, brown, etc.)
• Luster: Adamantine
• Streak: Colorless (does not produce a streak on a streak plate due to its hardness)

Physical Characteristics

• Crystal Habit: Octahedral, dodecahedral, cubic, or combinations thereof. Also massive (bort, carbonado).
• Cleavage Type: Perfect octahedral {111}.
• Fracture Type: Conchoidal to uneven.
• Tenacity: Brittle, despite its hardness, it can be fractured along cleavage planes or by sharp impact.
• Luster Type: Adamantine.

Formation

Diamonds form under extreme pressure and high temperature conditions deep within the Earth's mantle, typically at depths of 140 to 190 kilometers (87 to 118 miles). These conditions are found in the cratonic roots of continental plates. Temperatures range from 900 to 1300 degrees Celsius (1652 to 2372 degrees Fahrenheit), and pressures are between 4.5 and 6 gigapascals (GPa). They are brought to the surface rapidly through explosive volcanic eruptions, primarily in kimberlite and lamproite pipes, which are carrot-shaped igneous intrusions.

Usage

Diamonds are highly valued as gemstones due to their exceptional hardness, brilliance, and rarity. Industrial applications include cutting, grinding, drilling, and polishing tools, as well as in high-precision machinery, scientific research (e.g., diamond anvil cells for high-pressure experiments), and electronics (e.g., heat sinks).

Age Distribution

Diamonds range in age from approximately 990 million years to over 4.2 billion years, with most commercial diamonds being between 1 and 3.5 billion years old. This makes them among the oldest materials on Earth.

Where to Find

Finding Tips

Similar Rocks

Scientific Classification

Mineral Class

Native Elements

Group

Carbon Group

Crystal System

Isometric (Cubic)

Chemical Formula

C

Composition

Pure carbon

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