Petrographic Microscopy Flashcards
White light cannot be used because ……
Instead, monochromatic light is used because….
It’ll split into rainbow colours when it passes through the mineral
It has a single wavelength of single frequency.
A diamond is isotropic, therefore it appears….
Dark and stays dark on rotation of stage.
The refractive index doesn’t change with the direction of light as the sample is rotated.
Used to analyse…..
Minerals in rocks
Thin sections of rock must be flat to……
Ensure consistency on surface
Thin sections should be …… Thick
30 micro metres
Used to distinguish between………. Minerals and study the crystal structure.
Anisotropic and isotropic minerals
Sample is viewed using…..
Polarised white light
A polarising filter allows……
Only one plane of light, instead of two, to pass through.
The plane of light that passes through the filter is…..
The plane-polarised light.
The polarised light is…..
Transmitted through the sample
The reflective index (n) is….
The change in the speed of light between the air and the sample.
n = c / v
v is unique for each mineral.
A second polarising filter is added, an analyser, this removes…..
The issue of double refraction in anisotropic minerals.
The analyser cuts the path of emergent light so that the sample is…..
In cross polars. Light passes through depending on how sample is rotated.
The birefringence is when two rays of light undergo different refractive indices, the use of a…….
Prism allows them to meet up again to get a colour, not white light.
