Aquamarine & Muscovite
Did you know?
Before clear glass was common, crystals of beryl, the group that includes aquamarine, were ground into some of the first eyeglass lenses. The link still shows in German, where the word for glasses, Brille, comes straight from beryl.
Muscovite splits into thin, clear, heat-resistant sheets, and old Russia exported them as window panes known as Muscovy glass, the source of the mineral's name.
