The earliest examples of glass in the historical record were produced by natural phenomena. Obsidian is a black glass that men of the Pleistocene Era used to create tools and implements for cutting; and in Egypt, the intense heat of lightening or meteor strikes in the desert sands produced desert glass, which was used in jewelry and personal adornments.
Over time, man discovered the secrets of glass manufacture. The principal component of all glass is sand, but sand alone requires inordinately high amounts of energy in order to heat it to its melting point of nearly 1700°C.
By adding soda ash, or sodium carbonate, the melting point is reduced by more than half to 800°C. However, the result, commonly referred to as water glass, is water soluble, and would lose its integrity over time if used to hold liquids.
To maintain the chemical integrity of the glass and render it chemically inert, glassmakers began to add limestone to the mix in order to add various metal or metalloid oxides, like magnesium, aluminum and calcium oxides.
The oxides play double duty in that they render the final glass product chemically inert, and they disrupt the intermolecular bonding of the silica molecules, thereby doing away with a rigid, crystalline, latticed molecular structure altogether in favor of an irregular network of intermolecular bonds.
This irregular network has earned glass the classification of 'amorphous solid', because it is a rigid material that lacks the organizational periodicity of crystalline structures.
It is only once the glass is in its molten state that it can be formed, blown, pressed, rolled, or otherwise manipulated into the required form.