Glass is a substance, commonly made from heated silicon. Glass can form naturally and is also made artificially for use in windows and glass vessels and decorations.
In 2370, when Julian Bashir was attempting to locate a Horta in the mines of Davonia his tricorder had trouble singling it out as the mines had been drilled with high-powered phasers causing the walls to turn into glass, making the silicon lifeform difficult to detect amongst all the other silicon in the area. (DS9 novel: Devil in the Sky)
- Magnifying glass