The main ingredient in most sands is silica—silicon dioxide or, as it’s sometimes known, quartz. And since glass is, for want of a better phrase, melted sand, silica is also the primary ingredient in glass. But that silica content can vary significantly. The glasses we drink from or have in our window panes typically have about 70 per cent silica. The silica content of obsidian and of most tektites is generally between 65 per cent and 80 per cent. The silica content of Libyan desert glass, on the other hand, is a staggering 98 per cent. Not only did this make it the purest naturally occurring
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