Hi there,
Anyone know what determins the colours of micro crystals ?
Is it the thickness or angle or anything else ?
Micro Crystals
Moderators: rjlittlefield, ChrisR, Chris S., Pau
If you refer to micro crystals as in minerals, there may be different causes for the perceived color. Nevertheless, the most usual is the presence of atoms of certain elements, generally termed as chromofores. They either replace other elements in specific positions of the mineral lattice, or are included in the lattice as "impurities".
For example, Beryl is a mineral with a wide range of colors. The green variety, know as Emerald, owe its color to the presence of Chromium in its lattice. Likewise, the mineral amethyst, a variety of quartz, owe its purple color to the presence of Iron.
For example, Beryl is a mineral with a wide range of colors. The green variety, know as Emerald, owe its color to the presence of Chromium in its lattice. Likewise, the mineral amethyst, a variety of quartz, owe its purple color to the presence of Iron.
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Re: Micro Crystals
Thickness, orientation, and the nature of the material.Harald wrote:Hi there,
Anyone know what determins the colours of micro crystals ?
Is it the thickness or angle or anything else ?
...
Actually I was thinking of crystals I grow at home, like Ascorbic Acid or Citric Acid. The colors they make when I polarise the crystals.
Crystals of these materials are "optically active", which means that they rotate the angle of polarized light. The amount of rotation can depend on the wavelength of the light, in addition to the thickness, orientation, and nature of the material.
Suppose you cross polarizers so as to give complete extinction, and then place optically active crystals between them. In that case, polarized light going through the crystals gets rotated so that it is no longer completely blocked by the second polarizer. The crystals then appear bright against a black background. When the amount of rotation depends on wavelength, then different amounts of different colored light gets through, and then the crystals appear colored.
Most situations are more complicated, but the general principle is the same. The crystals change the polarization of light that goes through them, which causes more or less light to be blocked by the second polarizer, and this effect depends on wavelength = color of the light. If the rotation is such that mostly green light gets through, then the crystals appear green, and so on.
--Rik
Hi Harald.
The colors of materials under polarized light are related to a couple of properties that you might want to search in the internet: "Birefringence" and "Interference colors".
Simplifying a lot, the materials can be divided into isotropic and anisotropic. In the anisotropic materials, the light crossing them have different speeds at different directions. That difference is what create the birefringence, while the magnitude of that difference is what create the interference color gamut.
In opposition, in the isotropic materials, the light moves at the same speed in any given direction, looking completely black under crossed polarizers.
JL
The colors of materials under polarized light are related to a couple of properties that you might want to search in the internet: "Birefringence" and "Interference colors".
Simplifying a lot, the materials can be divided into isotropic and anisotropic. In the anisotropic materials, the light crossing them have different speeds at different directions. That difference is what create the birefringence, while the magnitude of that difference is what create the interference color gamut.
In opposition, in the isotropic materials, the light moves at the same speed in any given direction, looking completely black under crossed polarizers.
JL