Moonstone-Orthoclase | Gemopedia

Moonstone is a variety of feldspar that displays an amazing optical phenomenon called, adularescence. Internally repeating feldspar layers scatter the light that enters the stone creating a mystical white glow reminiscent of moonbeams. This glow comes to life, rolling across the gems surface, when it is moved. Traditionally, adularescent orthoclase gems have been called moonstone, however, other varieties of feldspar also exhibit this magical effect, including labradorite.
Alternate
Names
Star Moonstone
Colors
Colorless To White, Orange, Yellow, Brown

Moonstone-Orthoclase Classification

Common Name

Moonstone-Orthoclase

Species

Orthoclase

Variety

Moonstone

Colors

Colorless To White, Orange, Yellow, Brown

Alternate Names

Star Moonstone

Gemstone Groups

Feldspar

Key Separations

RI, biaxial interference figure in polariscope and magnification. Fluorescence and SG might also be useful.

Comments

Moonstone can also be labradorite feldspar.

Moonstone-Orthoclase Optical Properties

Transparency

Semitransparent - Opaque

Refractive Index

1.518-1.526
Tolerance:(+0.010/-0.010)

Birefringence

0.005-0.008

Optic Character

Biaxial

Optic Sign

Negative

Polariscope Reaction

Doubly Refractive (DR)

Fluorescence

SWUV: inert to weak pink to red or orange
LWUV: inert to weak yellowish white, blue, pink or red

CCF Reaction

Pleochroism

Unobservable

Dispersion

Comments

Moonstone-Orthoclase Chemistry & Crystallography

Chemical Name

potassium aluminum silicate

Chemical Formula

KAlSi3O8

Synthesis

Crystal System

Monoclinic

Classification

Silicate

Nature

Natural

Crystallinity

Polycrystalline

Comments

Moonstone-Orthoclase Characteristic Physical Properties

Hardness

6

Streak

White

Specific Gravity

2.55-2.61 Range:+/-0.03 Typical:2.58

Toughness

Poor

Inclusions

Moonstone will have blue or white adularescence. Stones might have centipede like inclusions and material with aventuresence or asterism might contain reflective inclusions such as fine needles or elongated hematite platelets.

Luster

Vitreous

Stability

Good

Fracture

Uneven, Splintery

Cleavage

Perfect, in two directions

Comments

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