Adularescence

Adularescence in moonstone including cause, types of moonstone, quality factors, and distinction from labradorescence.

By Fabian Moor Last updated
phenomena/adularescence moonstone species/feldspar schiller

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. [1]

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. [1][2]

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

Care Considerations

References

  1. ↑ 1. Read, P. (2014). Gemmology (3rd ed.). Butterworth-Heinemann/Routledge. DOI: 10.4324/9780080507224.
  2. ↑ 2. Nassau, K. (2001). The Physics and Chemistry of Color (2nd ed.). Wiley-Interscience. ISBN: 978-0-471-39106-7.
  3. ↑ 3. Schumann, W. (2009). Gemstones of the World (4th ed.). Sterling. ISBN: 978-1-4027-6829-3.

Related Topics

Feldspar GroupLabradorescence