Glass occurs naturally when rocks high in silicates melt at high temperatures and cool before they can form a crystalline structure. Obsidian or volcanic glass is a well known example of naturally occurring glass, although it can also be formed by a lightning strike on a beach, which contains silicate-rich sand.
Early forms of glass were probably rife with impurities and subject to cracking and other instability, but examples of glass beads, jars, and eating materials first appeared in ancient Egyptian culture.
When manufactured by humans, glass is a mixture of silica, soda, and lime. Other materials are sometimes added to the mixture to “frost” or cloud the glass or to add color. The elements of glass are heated to 1800° Fahrenheit (982° Celsius).
The resulting fused liquid can be poured into molds or blown into various shapes, and when cooled, glass is a strong, minimally conducting substance that will not interact with materials stored inside. As a result, glass is frequently used in scientific laboratories to minimize inadvertent chemical reactions and to insulate power lines.
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