There are some standard accessory plates used with a polarizing microscope to examine the optical properties of minerals. Some of the accessory plates are (i) quartz wedge, (ii) gypsum plates, and (iii) mica plates.
(1). Quartz Plates: The quartz wedge is a very thin wedge-shaped plate of quartz in which the fast vibration direction is parallel to its length. When a quartz wedge is moved forward in the microscope slot, the first order, second order, third order and so on, interference colours are produced successfully.
(2). Gypsum Plate: This plate is made by cutting a gypsum crystal (a calcium mineral) to such a thick that it produces a first order red interference colour between cross polars. Gypsum plate has fast vibration direction along its lenght. This plate is also called ”sensitive tint plate”, because with a slight increase in double refraction, it gives a blue colour and with a corresponding decrease, its colour changes to yellow.
(3). Mica Plate: The mica plate is also called ”quarter waves plate”. This plate consists of a thin cleavage flake of muscovite, which produces a path difference of a quarter of a ave length of yellow light.
- Isotropic and An-isotropic minerals
- Double Refraction of light in minerals
- Uni-axial Minerals
- Bi-axial Minerals
- Optical Indicatrix of Minerals
- Polarized Light Microscope
- Examination of Minerals under Polarized Light Microscope
- Examination of minerals in cross polar
- Extinction in minerals and Types of extinction