An inorganic glass is an amorphous solid whose local chemical network becomes rigid without developing long-range crystalline order.

Many familiar oxide glasses are built from network-forming units. In silica-based glass, for example, a silicon atom is locally coordinated by four oxygen atoms in a tetrahedral arrangement. These local units connect into a network whose bonds are organized at short range but do not repeat periodically throughout the material.

Adding network modifiers changes connectivity. In silicate glasses, modifier ions can break some bridging bonds, making the network easier to rearrange during forming while also changing chemical durability, thermal expansion and other properties.

As the disordered network passes through its glass-transition range, structural rearrangement becomes too slow or fast relative to the observation time. The exact apparent $T_g$ therefore depends on thermal history rather than behaving like one equilibrium crystal-melting temperature.

Cooling rate also controls whether a glass forms at all. Slow cooling gives a liquid more opportunity to nucleate and grow crystals; sufficiently rapid cooling can bypass crystallization and preserve an amorphous network.

Glasses combine optical transparency, chemical stability and formability with brittleness and flaw sensitivity. Their properties are therefore controlled by both network chemistry and the thermal history that determines structural relaxation and residual stress.