Last Updated: Jul 14, 2017     Views: 46

Glass scientists and engineers often refer to glass as an amorphous solid. According to the Schott Guide to Glass (page 17), 1996, "Glass includes all materials which are structurally similar to a liquid. However, under ambient temperature they react to the impact of force with elastic deformation and therefore have to be considered as solids." I liked the summary of the "debate" at this website:

Here are some more thorough definitions


From Pfaender, Heinz G. Schott Guide to Glass.  London: Chapman & Hall, 1996, p. 17:


"Scientists have several answers to the question: 'What is glass?'  One of the most popular is 'Glass is an inorganic product of melting, which when cooled without crystallization, assumes a solid state', or: 'A frozen supercooled liquid is called glass.'

"Actually, glass acts as an extremely viscous liquid which deforms very slowly under external force at normal temperatures.  The naked eye cannot detect the deformation, but there are scientific procedures to calculate and measure it.

"The following definition is more precise: Glass includes all materials which are structurally similar to a liquid.  However, under ambient temperature they react to the impact of force with elastic deformation and therefore have to be considered as solids.  In a more limited sense, the term 'glass' denotes all inorganic compounds which possess these basic qualities.  At the same time, a clear line is drawn in comparison to plastics.  Plastics are organic in nature and should never be designated as glass even if they are transparent."


2) From: Adams, P. Bruce, All About Glass. Corning, NY: Corning Glass Works, 1984, p. 2-3:


"If we view glass from the inside out -- in terms of how the substance is assembled -- we find that glass is an unusual material. It is mechanically rigid and, in this sense, behaves like a solid.  However, the atoms within the glass are arranged in a random or disordered fashion.  Such disordered structure is characteristic of a liquid.  In contrast, each atom in a crystalline solid is held in a definite position within a structural pattern or lattice. 

"In glass the atoms, though arranged at random, are frozen in position.  Thus, glass combines some of the aspects of a crystalline solid and some of the aspects of a liquid.  Its state may be described as vitreous or glassy.

"The raw materials from which glass is made are crystalline, but when those materials are melted, atoms become detached and move about in a random manner.  As the molten material cools, the atoms try to re-establish the ordered pattern they once had.  If the melt cools rapidly, it thickens and sets, or is fixed in a random structure before regular rearrangement can take place.  However, if the rate of cooling is slow enough, some crystals will form.  The crystalline state is the natural arrangement to which the atoms try to return.  But, under the rates of cooling normally encountered in glass manufacture, the atoms are not quick enough and they are trapped in a disordered structure.  Growth of crystals in glass is called devitrification....."


"It may seem strange that glass is a noncrystalline material and fine art glass is called crystal.  The designation "crystal" was created many years ago when someone looked at a piece of exceptionally brilliant glass and described it as being 'clear as crystal.'"


On p. 4:

"The most frequently used definition of glass is that adopted by the American Society for Testing and Materials: 'Glass is an inorganic product of fusion which has cooled to a rigid condition without crystallizing.'"


Here are several sites that you may want to look into:

I am attaching a brief list of articles and books which address this subject, in case you want to read further.