Alexandrite effect
The alexandrite effect , also known as shimmering , is a change in the color of a mineral caused by the light source . The effect was named after the alexandrite gemstone ( chrysoberyl with color change), but is also used for other minerals with the same effect. The alexandrite effect arises as a combined effect - character of the light source, - spectral absorption of the material, - the sensitivity of the eye.
The alexandrite appears emerald green in daylight, cherry red in candlelight or incandescent lamp light. Substances with the alexandrite effect are characterized by at least two spectral ranges with low absorption (high light transmission) and a range in between with strong absorption.
The cause of this are atoms of transition metals in the mineral . When Alexandrite it is often diadoch intercalated chrome . Other atoms such as vanadium , manganese or iron can modify the color change of the alexandrite.
The atoms light up in different colors under different light wave frequencies. For example, fluorescent tubes do not produce a color change from green to red, since the light waves emitted are too similar to daylight (see also light colors of lamps ). Candlelight, on the other hand, is ideally suited to bring about this, it contains a high proportion of yellow light.
Daylight, incandescent lamp light and candlelight are approximately like radiation from a black body and the character can be specified with a temperature: 6200, 2700 and 1500 K respectively . The spectrum is continuous and the higher the temperature, the shorter the wavelength of the maximum. The light from a fluorescent lamp is discontinuous and contains mercury spectral lines. The light from LED bulbs is also discontinuous.
When assessing what color a mineral appears in the light of a particular light source, eye sensitivity must also be considered. The human eye is most sensitive to green light. The eye is less sensitive to light with wavelengths longer than 650 nm (also red).
The alexandrite effect has also been observed in certain cases with other minerals. These include fluorite , corundum ( sapphire ), kyanite , monazite , spinel , some garnets and tourmalines as well as rare earth - Oxalatminerale as Coskrenit- (Ce) and Zugshunstit- (Ce) .
The alexandrite has another color-changing property, the pleochroism (direction-dependent color change). This must not be confused with the alexandrite effect. In an artificially produced alexandrite dichromatism (layer thickness or concentration-dependent color change, also called the Usambara effect) has been observed.
See also
literature
- E. Gübelin, K. Schmetzer, Gemstones with Alexandrite Effect, Gems & Gemology, winter 1982, p 197-203, pdf, http://www.gia.edu/gems-gemology/winter-1982-alexandrite-effect-gubelin , then print / select "DOWNLOAD PDF", in English, read July 4th, 2016
- Alexandrite, The Tsarstone collection http://www.alexandrite.net/chapters/chapter5/index.html in English, read July 4, 2016
- Gemlab.UK Through my spectroscope http://www.gemlab.co.uk/Through%20my%20Spectroscope.html , then find below "July 2012, The relationship between Color Change, Pleochroism and Absorption Spectra in Alexandrite", in English, read July 4th, 2016
Individual evidence
- ^ Kurt Nassau: The origens of color in minerals . In: American Mineralogist . tape 63 , no. 3-4 , 1978, pp. 221 (English, minsocam.org [PDF; accessed June 26, 2019]).
- ^ WB White, R. Roy, J. McKay Crichton: The "alexandrite effect": and optical study . In: The American Mineralogist . tape 52 , no. 5-6 , 1967, pp. 867 (English, minsocam.org [PDF; accessed June 26, 2019]).
- ↑ Jennifer Stone-Sundberg: Challenges in Orienting Alexandrite: The Usambara and Other Optical Effects in Synthetic HOC-Grown Russian Alexandrite. In: www.gia.edu. GIA (Gemological Institute of America Inc), accessed June 26, 2019 .