What is Adularescence?
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| Moonstone’s unearthly glow is caused by light scattering between microscopic layers of feldspar. Photo: G. Cedric |
Adularescence is an optical phenomenon that is produced in gemstones such as moonstones. Adularescence is the metallic iridescence originating from below the surface of a stone, that occurs when light is reflected between layers of minerals.
The effect of adularescence, also commonly referred to as schiller or shiller, is best described as a milky, bluish luster or glow originating from below the surface of the gemstone. The schiller, appearing to move as the stone is turned (or as the light source is moved), gives the impression of lunar light floating on water (accounting for moonstone's name).
As an optical phenomenon, adularescence exists only in the presence of light; it is a product of the interaction between light and the internal microstructures of the mineral and not a property of the mineral itself. The effect is produced by alternating layers of two types at a scale near the wavelength of light (c. 0.5 micron) – this leads to light scattering and interference.
Cause of Adularescence in Blue Moonstone
Blue Moonstone is a gem from the feldspar group and is composed of layers of albite – potassium rich aluminium silicate and orthoclase – sodium rich aluminum silicate. The schiller is produced because of light interference caused by the light having to weave its way through the layers with slightly different optical properties. The adularescence is caused by scattered light passing through the exsolution lamellae that act as scattering centres, creating a bluish hue/ lustre.See also:
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