How to identify Peridot

To correctly identify Peridot (Olivine (Mg,Fe)2SiO4), 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 yellowish-green to pure green, sometimes brownish-green. The intensity of green depends on the iron content.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous (glassy) to oily.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Often granular in massive forms; individual crystals are typically stubby prismatic.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Orthorhombic system; typically short, stout prismatic crystals, often with striations. Also found as rounded grains or massive aggregates.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Poor to indistinct in two directions (parallel to {010} and {110}), often exhibiting conchoidal fracture more readily than cleavage.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Mafic and ultramafic igneous rocks (basalt, gabbro, peridotite, dunite), mantle xenoliths, certain metamorphic rocks (dolomitic marbles), and pallasite meteorites.

Key Facts

Hardness

6.5-7 on Mohs scale

Specific Gravity

3.27-3.37 (increases with Fe content)

Crystal System

Orthorhombic

Color

Yellowish-green, olive green, brownish-green

Luster

Vitreous to oily

Transparency

Transparent to translucent

Fracture

Conchoidal

Cleavage

Poor to indistinct in two directions ({010} and {110})

Composition

Magnesium iron silicate (Mg,Fe)2SiO4

Physical characteristics

• Crystal Habit: Stubby prismatic crystals, granular, massive
• Cleavage Type: Poor to indistinct, {010} and {110}
• Fracture Type: Conchoidal
• Tenacity: Brittle
• Luster Type: Vitreous to oily

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