How to identify Sunstone

To correctly identify Sunstone (Oligoclase (feldspar group)), 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 yellow, orange, pink, red, or green, often with a metallic glitter from inclusions.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous to sub-vitreous on cleavage surfaces; aventurescent (spangled) due to inclusions.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Crystalline, often granular or massive. Individual crystals can be tabular or prismatic.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Typically anhedral to subhedral grains in igneous and metamorphic rocks. Well-formed crystals are monoclinic (for orthoclase component) or triclinic (for albite-anorthite series, including oligoclase), often tabular or prismatic.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Two distinct cleavages at approximately 90 degrees (86-94 degrees), characteristic of feldspars.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Felsic to intermediate igneous rocks (volcanic and plutonic), some metamorphic rocks, and placer deposits.

Key Facts

Hardness

6 to 6.5 on the Mohs scale

Specific Gravity

2.62 to 2.68

Crystal System

Triclinic

Color

Colorless, yellow, orange, pink, red, green, often with metallic glitter (aventurescence).

Luster

Vitreous to sub-vitreous, with aventurescence.

Transparency

Transparent to translucent.

Fracture

Uneven to conchoidal.

Cleavage

Perfect on {001} and good on {010}, intersecting at approximately 86-94 degrees.

Composition

Sodium calcium aluminum silicate, (Na,Ca)(Al,Si)AlSi2O8, with NaAlSi3O8 (albite) content between 70% and 90% and CaAl2Si2O8 (anorthite) content between 10% and 30%.

Physical characteristics

• Crystal Habit: Typically anhedral to subhedral grains, massive, or in tabular to prismatic crystals.
• Cleavage Type: Perfect on {001} and good on {010}, forming two planes at nearly 90 degrees.
• Fracture Type: Uneven to conchoidal.
• Tenacity: Brittle.
• Luster Type: Vitreous to sub-vitreous, with aventurescence.

Explore Sunstone