How to identify Peridot

To correctly identify Peridot (Olivine), 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 olive-green or 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 or massive. Individual crystals are typically euhedral to subhedral, often with a somewhat rounded appearance in volcanic rocks.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Orthorhombic system. Crystals are typically short prismatic, often tabular or equant. In granular aggregates, individual grains are anhedral to subhedral. Gem-quality crystals can be well-formed.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Poor to indistinct in two directions (parallel to {010} and {110}), often appearing as conchoidal fracture rather than true cleavage. This poor cleavage is a key distinguishing feature.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in mafic and ultramafic igneous rocks (e.g., basalt, gabbro, peridotite, dunite), metamorphic rocks derived from these, and as xenoliths in volcanic rocks. Also found in some meteorites.

Key Facts

Hardness

6.5-7 on the Mohs scale

Specific Gravity

3.27-3.37 (higher with increasing iron content)

Crystal System

Orthorhombic

Color

Yellowish-green, olive-green, pure green, brownish-green

Luster

Vitreous to oily

Transparency

Transparent to translucent

Fracture

Conchoidal to uneven

Cleavage

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

Composition

Magnesium iron silicate, (Mg,Fe)2SiO4

Physical characteristics

• Crystal Habit: Short prismatic, tabular, equant, granular, massive
• Cleavage Type: Poor to indistinct, often appearing as fracture
• Fracture Type: Conchoidal to uneven
• Tenacity: Brittle
• Luster Type: Vitreous (glassy) to oily

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