Glass is the main material that is used to make mirrors and glass is simply silicate heated to extreme temperatures. That puts it in a liquid state but because glass only reflects about 4% of the light available off of its surface reflection will be very poor. A little thin layer of metal is also placed behind the glass such as aluminum or silver in high-quality mirrors to ensure that the reflection is clear, and the mayor can be used as intended.
Mirrors have been made with different materials throughout the years. Before modern technology mirrors were made by simply placing aluminum behind a thin sheet of glass. Nowadays, mirrors are made similar but using finely ground obsidian rock behind a piece of glass.