According to the ease with which an object can change its shape and volume, the state of material aggregation can be divided into three types: solid, liquid and gas. Among solid objects, some objects have a certain melting point, which is called crystal. In a crystal, the particles that make up the crystal (such as molecules, atoms, ions, etc.) are regularly arranged in a periodic manner in three-dimensional space to form a certain form of lattice, and its properties vary with direction, which is an anisotropic body.
Other objects do not have a certain melting point. As the temperature rises, their fluidity continues to increase, and they gradually transition to a liquid state, which is called an amorphous body. Each part of it has the same properties and does not vary with direction, which is an isotropic body.
All molten substances have the conditions not to form crystals when cooled. All amorphous objects obtained by the method of "supercooling" melts, regardless of their chemical properties and solidification temperature range, are collectively called glass. Moreover, the mechanical properties of its solid are obtained due to the sharp increase in viscosity; at the same time, the transition from liquid to glass state is reversible.