Adularescence
Adularescence in moonstone including cause, types of moonstone, quality factors, and distinction from labradorescence.
Introduction
Adularescence is the soft, billowy, bluish-white glow that moves across moonstone.
It appears to float just below the surface and has a distinctly ethereal quality,
unlike the sharper flashes of labradorescence.
Named after Mount Adula in the Swiss Alps, where fine moonstone was historically
found, adularescence is the defining phenomenon of gem moonstone.
Cause
The physics behind adularescence:
Feldspar Structure
Moonstone is a feldspar with alternating layers of orthoclase and albite
created during slow cooling (exsolution). When these layers are thin
enough (approaching the wavelength of light), they scatter light through
interference.
Layer Thickness and Colour
- Thin layers (~0.1 μm): Produce blue schiller (most valued)
- Thicker layers: Produce white schiller
- Very thick layers: No adularescence
The thinner the layers, the shorter the wavelength scattered,
producing the prized blue glow.
Types of Moonstone
| Type | Feldspar | Adularescence | Body Colour |
|---|---|---|---|
| Classical moonstone | Orthoclase | Blue-white schiller | Colourless to grey |
| Rainbow moonstone | Labradorite | Multicoloured flashes | Translucent white |
| Peach moonstone | Orthoclase | White schiller | Peach to orange |
| Grey moonstone | Orthoclase | Blue schiller | Grey body |
Rainbow Moonstone Note
Quality Factors
Assessing moonstone quality:
Schiller Quality
| Factor | Premium Quality |
|---|---|
| Schiller colour | Blue (most valued) |
| Intensity | Strong, visible adularescence |
| Centering | Schiller centred on dome |
| Coverage | Covers most of dome surface |
| Movement | Smooth, floating motion |
Body Quality
- Transparency: More transparent = higher value
- Body colour: Colourless to light grey preferred
- Clarity: Fewer inclusions better
- Cut: Well-proportioned cabochon
Sources
| Origin | Characteristics |
|---|---|
| Sri Lanka | Finest blue moonstone; historic source |
| India | Large production; variable quality |
| Myanmar | Some fine material |
| Tanzania | Good quality available |
| Madagascar | Various qualities |
Adularescence vs Labradorescence
Adularescence (Moonstone)
- Single-colour glow (blue or white)
- Soft, billowy appearance
- Appears to float below surface
- Caused by layer interference
- Orthoclase feldspar
Labradorescence (Labradorite)
- Multiple spectral colours
- Sharp, distinct flashes
- Appears on surface
- Caused by twinning interference
- Plagioclase feldspar
Cutting for Adularescence
Proper orientation is critical:
- Cut as cabochon (faceting destroys effect)
- Orient to show schiller through dome
- Appropriate dome height
- Symmetrical shape for even display
- Polish quality important for clarity