Glass

Glass is a generic term of any molten silicon which can be naturally-occurring (volcanic) or man-made and is by definition very fragile. Glass is most commonly used in windows and glasses, both drinking and the visual aid.

On Admiral Kirk's birthday in 2285, Doctor McCoy gave him a pair of reading glasses possibly as a slight against Kirk's age. The glasses later were broken in a battle with the USS Reliant commandeered by Khan Noonien Singh. The glasses were sold in 20th century Earth at an antiques dealer in San Francisco who purchased them for US$100, noting they would have been worth more if the lenses were intact. 

An invidium contamination aboard the USS Enterprise (NCC-1701-D) caused a drinking glass to melt in the hand of its holder, lieutenant junior grade Duffy releasing the beverage from within. 

Glass was one of the words Doctor Julian Bashir used after he was infected by the aphasia virus in 2369. 

One form of glass is Tabalian glass. 

After she was beamed aboard the USS Enterprise (NCC-1701-E) Lily Sloane was surprised seeing no glass closing a hatch to space. Jean-Luc Picard then demonstrated her the function of a force field.