Labradorescence
Labradorescence in labradorite and spectrolite including cause, colour range, quality factors, and distinction from adularescence.
Introduction
Labradorescence is the striking polychromatic colour play seen in labradorite
feldspar: broad, directional flashes of blue, green, gold, orange, and purple
that appear and vanish as the stone is tilted. First identified in specimens
from Labrador, Canada in 1770, [1] it is wholly
distinct from the soft single-colour glow of adularescence.
The cause is thin-film interference within the Bøggild intergrowth: repeated
lamellae of two plagioclase compositions (approximately An47–An58) form during
slow cooling, creating a periodic lamellar structure whose spacing is comparable
to visible wavelengths. Different lamella thicknesses selectively reflect
different wavelengths, producing spectral colours in distinct patches rather
than the uniform scattered glow of moonstone schiller. [2]
Finnish spectrolite, labradorite with an unusually complete colour range from
violet through red, shows all spectral colours in a single specimen and
commands premium prices among collectors. [3]
Mechanism
The cause of labradorescence:
Lamellar Twinning
- Caused by light interference from repeated thin twin layers
- Twin lamellae form during cooling of plagioclase
- Lamellae vary in thickness, producing different colours
- Light interferes between twin boundaries [2]
Orientation Dependence
- Most prominent on specific crystal planes (001 cleavage)
- Requires proper cutting orientation to display effect
- Colours appear in patches or broad flashes
- Tilting the stone reveals different colour areas
Colour Range
Labradorescence can display nearly the full spectrum:
- Blue: Most common colour seen
- Green: Often with blue
- Gold/yellow: Warm tones
- Orange: Vivid examples exist
- Red: Rarer; highly prized
- Purple: Less common
Multiple colours in one stone are typical and valued.
Spectrolite
Quality Factors
| Factor | Premium Quality |
|---|---|
| Colour range | Multiple vivid colours (spectrolite type) |
| Intensity | Bright, strong flashes |
| Coverage | Large percentage of surface shows effect |
| Flash size | Large, distinct colour areas |
| Body darkness | Darker body enhances colours |
Sources
| Origin | Characteristics |
|---|---|
| Finland | Spectrolite; full colour range |
| Labrador (Canada) | Type locality; blue-green common |
| Madagascar | Good labradorescence; various colours |
| Russia | Quality material available |
| Ukraine | Some production |
Labradorescence vs Adularescence
Labradorescence
- Multiple spectral colours
- Sharp, distinct flashes
- Colours appear in patches
- Caused by lamellar twinning
- Plagioclase (labradorite)
- Effect at surface level
Adularescence
- Single colour (blue or white)
- Soft, floating glow
- Even, billowy appearance
- Caused by layer exsolution
- Alkali feldspar (orthoclase)
- Appears below surface
Cutting Considerations
Proper cutting maximises labradorescence:
Orientation
- Cut to display colours face-up
- Align with cleavage plane for best effect
- May sacrifice weight for optimal display
- Flat backs common to maximise colour area
Cut Styles
- Cabochons: Traditional; shows colours well
- Flat slabs: Maximises colour display area
- Faceted: Possible but reduces phenomenon visibility
- Carvings: Popular for decorative pieces
Market and Value
Labradorite market considerations:
- Spectrolite: Highest prices for fine Finnish material
- Collector stones: Fine multi-colour specimens valued
- Decorative use: Popular for tiles, countertops
- Jewellery: Growing popularity for unique pieces
- Size: Large pieces available (unlike many gems)
References
- ↑ 1. Schumann, W. (2009). Gemstones of the World (4th ed.). Sterling. ISBN: 978-1-4027-6829-3.
- ↑ 2. Miura, Y.; Tomisaka, T.; Kato, A. (1975). Labradorescence and the ideal behavior of thicknesses of alternate lamellae in the Bøggild intergrowth. Mineralogical Journal, 7(6), 526–541. DOI: 10.2465/minerj1953.7.526.
- ↑ 3. Read, P. (2014). Gemmology (3rd ed.). Butterworth-Heinemann/Routledge. DOI: 10.4324/9780080507224.