Goshenite has four properties that made it attractive to some of Europe’s early lens makers: 1) it is colorless, 2) it has exceptional clarity, 3) it is found in large crystals, and, 4) it has exceptional hardness. With a Mohs hardness of 7.5 to 8, goshenite was the material used in the earliest scratch-resistant lenses.

In the Middle Ages, goshenite crystals were cut and polished into lenses for hand magnifiers, telescopes, and some of the earliest eyeglasses. Its hardness was superior to the much more abundant quartz crystals. It was harder than any commonly encountered object that might scratch it. The German name “brille”, used for spectacles, may have been derived from beryll, the German name for beryl.