How to identify Black Diamond

To correctly identify Black Diamond (Carbon (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

   Opaque black to dark grey. The color is uniform throughout for carbonados, while inclusion-rich black diamonds may show variations or a slightly mottled appearance under magnification.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Sub-metallic to adamantine, often duller than typical gem diamonds due to porosity (carbonado) or dense inclusions.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Carbonados are typically rough, porous, and irregular in shape, often resembling charcoal or clinker. Inclusion-rich black diamonds can have a smoother surface if polished, but their internal texture is dense with inclusions.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Carbonados are polycrystalline aggregates, lacking a distinct external crystal form. Inclusion-rich black diamonds can occur as octahedral, dodecahedral, or cubic crystals, but their external form is often obscured by their opaque nature and rough surfaces.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None for carbonado due to its polycrystalline nature. For inclusion-rich black diamonds, perfect octahedral cleavage {111} is present but rarely observed due to their toughness and dense inclusions.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Carbonados are found in alluvial deposits, primarily in Brazil and the Central African Republic, suggesting a secondary depositional environment after their primary formation. Inclusion-rich black diamonds are found in kimberlite and lamproite pipes, similar to other gem diamonds, indicating a mantle origin.

Key Facts

Hardness

10 (Mohs scale)

Specific Gravity

3.10 - 3.53 g/cm³ (lower for porous carbonados, higher for dense monocrystalline diamonds)

Crystal System

Isometric (cubic)

Color

Opaque black to dark grey

Luster

Sub-metallic to adamantine, often dull

Transparency

Opaque

Fracture

Conchoidal to uneven (for monocrystalline diamond); irregular, granular (for carbonado)

Cleavage

Perfect octahedral {111} (for monocrystalline diamond); none (for carbonado)

Composition

Pure carbon (C)

Physical characteristics

• Crystal Habit: Carbonado: Polycrystalline aggregate, irregular masses. Inclusion-rich black diamond: Octahedral, dodecahedral, or cubic, often distorted or rounded.
• Cleavage Type: Perfect octahedral {111} (for monocrystalline diamond); absent (for carbonado).
• Fracture Type: Conchoidal to uneven (for monocrystalline diamond); irregular, granular (for carbonado).
• Tenacity: Brittle (for monocrystalline diamond); exceptionally tough (for carbonado due to its polycrystalline nature).
• Luster Type: Sub-metallic to adamantine, often dull.

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