Menu

Monthly archives: August, 2021

Biaxial minerals

Crystals belonging to orthorhombic, monoclinic, and triclinic systems have two optic axes and therefore they are called ”biaxial”. These optic axes intersect each other to form acute and obtuse angles. The acute angle between the two optic axes is called the ”optic axial angle” and is commonly designated as 2v. The plane containing the two …

Uniaxial minerals

The crystals of the tetragonal and hexagonal systems possess only one optic axis, which is parallel to the c-axis. For this reason, they are called ”uniaxial”. The optical characters of the uniaxial minerals may be summarized as follows: When a ray of light passes through a uniaxial crystal in any direction other than the optic …

Double Refraction

Double Refraction: When a ray of light passes through an an-isotropic crystal, it breaks into two polarized rays vibrating in mutually perpendicular planes. One ray which obeys laws of refraction is called ”ordinary ray” or ”O-ray”, and the second ray which does not obey these laws is called ”extraordinary ray” or ”E ray”. Ordinary Ray:┬áThe …

Isotropic and anisotropic minerals

Depending upon the optical properties, the minerals can be divided into two groups: (i) isotropic minerals and (ii) anisotropic minerals. Isotropic Minerals: In crystals belonging to the cubic system, the light travels with the same velocity in all directions and therefore each mineral has only one refractive index. Such minerals are called ”isotropic minerals”. Non-crystalline …

Refractive index of Minerals

When a ray of light passes from air into a denser medium such as glass, it gets refracted. In the glass the light travels with a lesser velocity than in air and deviates from its previous path. The amount of deviation depends on the angle of incidence and the relative velocity of light in the …

Optical Properties of Minerals

The optical properties of minerals are important for their identification. Optical properties are determined with the help of a ”polarizing microscope”. The study of optical properties of minerals is known as Optical Mineralogy. With the help of optical mineralogy, we study the minerals and rocks with the help of their optical properties. The rocks and …