Following are some properties of light:
Light travels in straight line.
Light forms shadows.
When light coming from the sun is blocked,eclipses are formed.
The optical properties of crystals are, next to x-ray diffraction and direct chemical analyses, the most reliable properties available to distinguish and identify minerals. The optical properties depend on the manner that visible light is transmitted through the crystal, and thus are dependent on crystal structure, crystal symmetry, and chemical composition of the mineral.
In order to understand the optical properties of crystals we must first understand something about light and how it interacts with matter.
Light
Light is electromagnetic radiation that has properties of waves. The electromagnetic spectrum can be divided into several bands based on the wavelength. As we have discussed before, visible light represents a narrow group of wavelengths between about 380 nm and 730 nm.
Our eyes interpret these wavelengths as different colors. If only a single wavelength or limited range of wavelengths are present and enter our eyes, they are interpreted as a certain color. If a single wavelength is present we say that we have monochromatic light. If all wavelengths of visible light are present, our eyes interpret this as white light. If no wavelengths in the visible range are present, we interpret this as dark.
Interaction of Light with Matter
Velocity of Light and Refractive Index
The energy of light is related to its frequency and velocity as follows: