Sanidine Gem Guide and Properties Chart

Sanidine is a potassium-rich feldspar which is related to amazonite (microcline) and orthoclase by its chemistry. Sanidine gems that display adularescence, a mystical internal glow, are called moonstone. Colorless to yellow and pale brown gems have been found in Germany, Mexico, and Madagascar.

General Information

Classification
Optical Properties
Characteristic Physical Properties
Chemistry & Crystallography

Common Name

Sanidine

Species

Feldspar

Transparency

Transparent - Translucent

Dispersion

Strength: Weak Fire Value: 0.012

Refractive Index

1.518-1.531

Birefringence

0.003-0.007

Optic Character

Biaxial

Optic Sign

Negative

Polariscope Reaction

Doubly Refractive (DR)

Fluorescence

SWUV: Inert to weak red-orange
LWUV: Inert to weak red-orange

Pleochroism

Unobservable

Hardness

6-6.5

Streak

White

Specific Gravity

Typical:2.600

Luster

Vitreous

Fracture

Conchoidal, Uneven

Cleavage

Perfect, in two directions

Chemical Name

Potassium or Sodium Aluminum Silicate

Chemical Formula

(K, Na)(AlSi₃O₈)

Crystal System

Monoclinic

Chemistry Classification

Silicate

Sanidine Colors

Brown
Yellow
Colorless

Countries of Origin

Unknown; Madagascar