How to identify Olivine

To correctly identify 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 olive-green, yellowish-green, or brownish-green. Can also be yellow, brown, or rarely colorless.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous (glassy) to greasy.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Granular aggregates are common. Individual crystals are typically stubby prismatic.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Orthorhombic system; typically forms stubby, equant, or tabular crystals. Often found as disseminated grains or granular masses in igneous rocks.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Poor to indistinct in two directions at 90 degrees, often appearing as conchoidal fracture rather than true cleavage.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Mafic and ultramafic igneous rocks (basalt, gabbro, peridotite, dunite), mantle xenoliths, and some metamorphic rocks (e.g., serpentinites, marbles).

Key Facts

Hardness

6.5-7 on the Mohs scale

Specific Gravity

3.2-4.3 (increases with Fe content; forsterite ~3.2, fayalite ~4.3)

Crystal System

Orthorhombic

Color

Olive-green, yellowish-green, brownish-green, yellow, brown, rarely colorless

Luster

Vitreous to greasy

Transparency

Transparent to translucent

Fracture

Conchoidal to uneven

Cleavage

Poor to indistinct {010} and {110}

Composition

Magnesium iron silicate

Physical characteristics

• Crystal Habit: Typically granular, massive, or as disseminated anhedral to subhedral grains. Individual crystals are usually stubby prismatic or tabular.
• Cleavage Type: Poor to indistinct, often masked by fracture. Two directions at approximately 90 degrees.
• Fracture Type: Conchoidal to uneven, brittle.
• Tenacity: Brittle
• Luster Type: Vitreous to greasy

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