How to identify Diamond in Kimberlite

To correctly identify Diamond in Kimberlite (Diamond (C) in Kimberlite), 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

   Kimberlite matrix is typically dark green, blue-green, or black, often weathering to brown or yellowish-brown. Diamonds within can be colorless, yellow, brown, or rarely other hues.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Kimberlite matrix is dull to earthy, sometimes greasy. Diamonds exhibit an adamantine (diamond-like) luster.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Kimberlite is porphyritic, with larger crystals (phenocrysts) of olivine, phlogopite, and garnet embedded in a fine-grained groundmass. Diamonds are typically discrete crystals within this matrix.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Diamonds often occur as euhedral to subhedral octahedra, dodecahedra, or combinations thereof, sometimes with rounded or etched surfaces. Kimberlite minerals show various crystal forms depending on the mineral species.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Diamonds possess perfect octahedral cleavage ({111}). Kimberlite minerals have variable cleavage (e.g., olivine has poor cleavage, phlogopite has perfect basal cleavage).

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Kimberlite occurs in diatremes (pipes), dikes, and sills, typically found in stable cratonic regions of ancient continental crust. These structures represent volcanic conduits that brought mantle material to the surface.

Key Facts

Hardness

Diamond: 10 (Mohs scale); Kimberlite minerals vary (e.g., olivine 6.5-7, phlogopite 2.5-3).

Specific Gravity

Diamond: 3.50-3.53 g/cm³; Kimberlite: 2.5-2.9 g/cm³ (variable depending on alteration and mineralogy).

Crystal System

Diamond: Isometric (cubic); Kimberlite: Polymineralic, individual minerals have their own crystal systems.

Color

Diamond: Colorless, yellow, brown, rarely pink, blue, green; Kimberlite: Dark green, blue-green, black, weathering to brown/yellow.

Luster

Diamond: Adamantine; Kimberlite: Dull, earthy, sometimes greasy.

Transparency

Diamond: Transparent to opaque; Kimberlite: Opaque.

Fracture

Diamond: Conchoidal to uneven; Kimberlite: Uneven to hackly.

Cleavage

Diamond: Perfect octahedral ({111}); Kimberlite: Variable, depending on constituent minerals.

Composition

Diamond: Pure carbon (C); Kimberlite: Ultramafic, potassic igneous rock composed primarily of olivine, phlogopite, serpentine, carbonates, and various accessory minerals (e.g., pyrope, chromite, ilmenite).

Physical characteristics

• Crystal Habit: Diamond: Octahedral, dodecahedral, cubic, or combinations, often rounded or etched. Kimberlite: Porphyritic, with phenocrysts of various minerals.
• Cleavage Type: Diamond: Perfect octahedral ({111}); Kimberlite: Variable, depending on constituent minerals.
• Fracture Type: Diamond: Conchoidal to uneven; Kimberlite: Uneven to hackly.
• Tenacity: Diamond: Brittle; Kimberlite: Brittle.
• Luster Type: Diamond: Adamantine; Kimberlite: Dull, earthy, greasy.

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