Solid liquid - and in it is not present a paradox. Yes, really there are substances which even in a firm state behave as liquid. On the other hand, in usual life very few people from people met substance firmer, than glass.
The stiffened liquid
If to be exact, then not stiffened, and overcooled. As glass keeps the main properties of liquid even in a habitual firm state. Objections are quite clear – the pier glass does not flow! Everything very just at the room temperature it almost does not flow, flows more true, but extremely slowly, but it is only worth heating it, the movement will become evident at once.
Heating of glass or product from it up to the temperature of 600 - 900 degrees completely changes its properties. Glass becomes soft and plastic that allows to give it any form.
It is peculiar to all amorphous substances which treats and flew down, it is also possible to include all pitches in this category both natural, and artificial, various glues, rubber separate types of plastics. Certainly, there is a difference in temperatures at which these substances lose hardness, but the principle is identical everywhere.
Crystal secret
The main difference of amorphous substances from crystal, that amorphous have no ordered crystal lattice. Keeping structure of near communications, amorphous substance has no distant order of arrangement of atoms and molecules. Thus, the isotropy of properties and lack of a certain melting point is typical for amorphous bodies. That is in process of temperature increase the amorphous bodies are gradually softened and imperceptibly turn into liquid state. From this it follows that crystalline solid differs from liquid not only quantitatively, but also is mainly quality. That is the amorphous body can safely be considered as liquid with infinitely big viscosity.
Glass riddles
As the mankind got acquainted with glass and when learned to develop it, it is already impossible to learn. It is obvious that acquaintance it began with natural analogs of glass - obsidians and tektit. It is known only that the most ancient of the products found for today of man-made glass the light green bead of 9х5.5 mm in size found in the neighborhood of the city of Thebes dated 35th year BC is considered. Pliny has also a legend how there was a glass as if dealers in soda, having moored to the coast, began to make a lunch. As they did not find suitable stones, they had to prop up coppers pieces of soda - and after a while soda was warmed and mixed up with river sand. There was a liquid unfamiliar earlier. In spite of the fact that attempts to repeat experiment were unsuccessful, the legend continues to live. Most likely, glass was received by people as a by-product when smelting copper.