For more detail on crystal lenses used by people as far back as the Old Kingdom Egypt, see “The Crystal Sun” by Robert Temple (deceased).
Most lenses are classified as “jewelry” and hidden in displays of such or are in museum basements. Many of they have dioptre measurements and were used as eyeglasses, others as lenses in tubes, ie telescopes.
Blurb:
https://www.robert-temple.com/crystalSunMain.html
Thanks PIF.