Лекция: GLASS HISTORY

NATURAL GLASSES

Natural glass has existed since the beginnings of time, formed when rocks melt as a result of high-temperature phenomena such as volcanic eruptions, lightning strikes or the impact of meteorites, and then cool and solidify rapidly enough so that a liquid-like structure can be frozen in glassy state. Rocks can be classified according to the way they form either from sediments or eruptions. The compositions of volcanic rocks do not differ significantly from sedimentary ones contrary to their respective thermal histories. It is well-known that glass formation is a kinetic phenomenon. Most well-known natural glass is obsidian that is believed to be one of the first glasses that appeared on earth at least 40 million years ago. Such an impressive age demonstrates that the vitreous state may be resistant in the long term against devitrification and water corrosion. Glass utilization would have started when stone-age people became aware of the strength and sharpness that could be obtained from obsidian. The formation of natural glasses may happen under three main conditions, the first two corresponding to a compromise between the glass composition (viscosity regime) and the cooling conditions.