How to identify Diopside

To correctly identify Diopside (CaMgSi2O6), 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

   Typically light to dark green, but can be colorless, white, gray, brown, or black. Chromian diopside is emerald green.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous to dull.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Crystals are typically prismatic, often with a square or octagonal cross-section. Can be granular or massive within the matrix.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Monoclinic system, typically forming short to long prismatic crystals with characteristic pyroxene cleavage angles (approximately 87° and 93°).

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Two distinct cleavages intersecting at nearly 90 degrees (specifically 87° and 93°), characteristic of pyroxenes.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Metamorphic rocks (marbles, skarns, calc-silicate gneisses), mafic and ultramafic igneous rocks (basalts, gabbros, peridotites, kimberlites).

Key Facts

Hardness

5-6 (Mohs scale)

Specific Gravity

3.22-3.38

Crystal System

Monoclinic

Color

Green, white, gray, brown, black, colorless

Luster

Vitreous to dull

Transparency

Transparent to opaque

Fracture

Uneven to conchoidal

Cleavage

Perfect on {110} at 87° and 93°

Composition

Calcium Magnesium Silicate (CaMgSi2O6)

Physical characteristics

• Crystal Habit: Prismatic, columnar, granular, massive
• Cleavage Type: Perfect in two directions, nearly at right angles (87° and 93°)
• Fracture Type: Uneven to conchoidal
• Tenacity: Brittle
• Luster Type: Vitreous to dull

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