How to identify Diamond

To correctly identify Diamond (Diamond), check each of these features in order. Many rocks and minerals look alike, so cross-reference multiple properties before deciding.

Step-by-step identification

1. 1

   Color

   Overall color and any zoning or banding

   Rough diamonds can be colorless, yellow, brown, gray, or rarely blue, green, pink, red, or black. The most common colors are yellow and brown due to nitrogen impurities.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Adamantine to greasy. Unpolished surfaces may appear dull or greasy due to surface coatings or etching.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Typically smooth to slightly rough on crystal faces, often with characteristic growth features like trigons (triangular pits) on octahedral faces, or striations on dodecahedral faces. Resorbed diamonds may have a frosted or etched appearance.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Most commonly octahedral, dodecahedral, or cubic. Combinations of these forms are also frequent. Macles (twinned crystals) are common. Irregular, rounded, or amorphous shapes (bort, carbonado) also occur.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Perfect octahedral cleavage in four directions {111}. This means it can be split along these planes, though it is difficult to initiate due to its hardness.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   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. Rarely found in ultra-high-pressure metamorphic rocks or impact structures.

Key Facts

Hardness

10 (Mohs scale), the hardest known natural mineral.

Specific Gravity

3.50 - 3.53 g/cm³ (for pure diamond). Can vary slightly with impurities.

Crystal System

Cubic (isometric)

Color

Colorless, yellow, brown, gray, green, blue, pink, red, black. Colorless is most prized for gems.

Luster

Adamantine (brilliant, like a diamond) to greasy (on rough or etched surfaces).

Transparency

Transparent to opaque. Gem-quality diamonds are typically transparent.

Fracture

Conchoidal to uneven. Despite its hardness, it can fracture.

Cleavage

Perfect octahedral {111} in four directions.

Composition

Pure carbon (C). Trace elements (e.g., nitrogen, boron) cause color variations.

Physical characteristics

• Crystal Habit: Octahedral, dodecahedral, cubic, or combinations thereof. Also macles (twinned crystals), bort (irregular aggregates), and carbonado (polycrystalline aggregates).
• Cleavage Type: Perfect octahedral {111}. This means it breaks cleanly along four specific planes, forming smooth, flat surfaces.
• Fracture Type: Conchoidal (shell-like, curved breaks) to uneven. This occurs when the diamond breaks in directions other than its cleavage planes.
• Tenacity: Brittle. Despite its extreme hardness, diamond can be fractured or cleaved by a sharp blow.
• Luster Type: Adamantine (for well-formed, clean surfaces) to greasy (for rough, etched, or coated surfaces).

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