Accessory plates used with polarizing microscope

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.

Related posts:

1. Isotropic and An-isotropic minerals
2. Double Refraction of light in minerals 
3. Uni-axial Minerals
4. Bi-axial Minerals
5. Optical Indicatrix of Minerals
6. Polarized Light Microscope
7. Examination of Minerals under Polarized Light Microscope
8. Examination of minerals in cross polar
9. Extinction in minerals and Types of extinction