Sunstone | Gemopedia

A gem known since ancient times, sunstone is a type of feldspar formed and crystallized in lava flows. Radiating with the power of eternal light, sunstone has been reportedly found in the tombs of Viking sailors who believed it would aid in their journey through both life and the afterlife. A distinguishing feature of sunstone is its metallic schiller, which rolls across the stone's surface. The effect is due to the presence of small plate-like inclusions of minerals such as hematite or native copper. These inclusions interfere with the passage of light, causing it to scatter. If the inclusions are larger and visible to the eye, they create glittery star-like reflections that gemologists refer to as aventurescence.

Sunstone Classification

Common Name

Sunstone

Species

Oligoclase

Variety

Sunstone

Colors

yellow, orange and brown

Alternate Names

Gemstone Groups

Group: Feldspar

Key Separations

Appearance, RI, birefringence, optic character and magnification. Adularescence in a stone indicates orthoclase.

Comments

Sunstone Optical Properties

Transparency

Semitransparent To Opaque

Refractive Index

1.539-1.547

Birefringence

0.007-0.01

Optic Character

biaxial

Optic Sign

negative

Polariscope Reaction

doubly refractive (DR) or AGG depending on transparency

Fluorescence

SWUV: Inert
LWUV: Inert

CCF Reaction

Pleochroism

Value: Usually none

Dispersion

Sunstone Chemistry & Crystallography

Chemical Name

calcium aluminum silicate

Chemical Formula

KAlSiO8

Synthesis

Crystal System

Triclinic

Classification

Silicate

Nature

Natural

Crystallinity

Crystalline

Sunstone Characteristic Physical Properties

Hardness

6

Streak

Specific Gravity

2.62-2.67 Range: +0.02/-0.03 Typical: 2.65

Toughness

Poor

Inclusions

Sunstones contain tiny reddish to golden or green platelets of hematite or goethite. Stones might show a four-rayed star with slivery adularescence if fine needles intersect.

Luster

Vitreous

Stability

Good

Fracture

Uneven To Splintery

Cleavage

Two Cleavage Directions, Parting Also Common

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