How to identify Rainbow Moonstone

To correctly identify Rainbow Moonstone (Moonstone (variety of Labradorite, a plagioclase feldspar)), 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

   Translucent to semi-transparent white or colorless body with a distinct iridescent play of colors (labradorescence) that can include blue, green, yellow, orange, and pink.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous to pearly.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Typically massive, granular, or in tabular crystals within host rock. When polished, it has a smooth, often slightly waxy feel.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Triclinic crystal system, typically occurring as anhedral to subhedral grains or tabular crystals. Rarely found as well-formed euhedral crystals.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Perfect cleavage in two directions, nearly at right angles (approximately 86° and 94°), characteristic of plagioclase feldspars.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in mafic igneous rocks (e.g., basalt, gabbro, anorthosite), some metamorphic rocks, and pegmatites. Often occurs in association with other feldspars, pyroxenes, and amphiboles.

Key Facts

Hardness

6 to 6.5 on the Mohs scale

Specific Gravity

2.68 to 2.72

Crystal System

Triclinic

Color

Translucent white to colorless with iridescent flashes of blue, green, yellow, pink, etc.

Luster

Vitreous to pearly

Transparency

Transparent to translucent

Fracture

Uneven to conchoidal

Cleavage

Perfect in two directions (pinacoidal), nearly at 90 degrees (86° and 94°)

Composition

(Na,Ca)(Al,Si)AlSi2O8 - a plagioclase feldspar, specifically labradorite

Physical characteristics

• Crystal Habit: Typically massive, granular, or in tabular crystals; rarely euhedral.
• Cleavage Type: Perfect in two directions, nearly perpendicular (pinacoidal).
• Fracture Type: Uneven to conchoidal.
• Tenacity: Brittle.
• Luster Type: Vitreous to pearly.

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