How to identify Grossular Garnet

To correctly identify Grossular Garnet (Ca3Al2(SiO4)3), 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

   Grossular garnet can be colorless, white, yellow, orange, reddish-orange (hessonite), brown, light green, or emerald green (tsavorite). The color is a key indicator, especially for the gem varieties.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous to resinous.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Typically granular or massive, but well-formed crystals exhibit smooth, often shiny faces.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Commonly dodecahedral (12-sided) or trapezohedral (24-sided) crystals, or combinations of these forms. Can also be anhedral (without well-formed faces) in massive aggregates.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None. Garnets are known for their lack of cleavage, exhibiting conchoidal to subconchoidal fracture.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Look for grossular in metamorphosed impure limestones, dolomites, marls, and skarns. It is often associated with minerals like diopside, wollastonite, vesuvianite, epidote, and calcite.

Key Facts

Hardness

6.5-7.5 on the Mohs scale

Specific Gravity

3.57-3.73 g/cm³

Crystal System

Isometric

Color

Colorless, white, yellow, orange, reddish-orange, brown, light green, emerald green

Luster

Vitreous to resinous

Transparency

Transparent to translucent

Fracture

Conchoidal to subconchoidal

Cleavage

None

Composition

Calcium aluminum silicate

Physical characteristics

• Crystal Habit: Typically dodecahedral, trapezohedral, or combinations; also massive or granular.
• Cleavage Type: Absent
• Fracture Type: Conchoidal to subconchoidal
• Tenacity: Brittle
• Luster Type: Vitreous to resinous

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