Crystals like calcite, quartz, ice and tourmaline having only one optic axis are called uniaxial crystals.
Crystals like mica, topaz, selenite and aragonite having two optic axes are called biaxial crystals.
Three basic types of crystals are:
- Single Crystals
- Poly Crystals
- Liquid Crystals
Single Crystals: Those crystals in which patterns are regular throughout the whole crystal are known as single crystals.
Polycrystals: If all the well maintained faces of the mono crystals are combined together then the resultant crystal formed is known as polycrystal.
Liquid crystals: Liquid crystals are not found in purely liquid form. These are basically fluids between the solids and liquids, which are formed upon heating some organic crystalline solids.