Glass

"Glass, you see, can't be broken with regular tools in Minecraft. Well, not without it shattering into a million tiny, invisible shards. Any experienced builder will always cook up more glass than they need for this exact reason - the tiniest slip and you'll have to make a lengthy trip back to the desert for more sand."

- Duncan Geere

Glass is a decorative fully transparent block which can be dyed into stained glass.

Obtaining
Glass will drop itself only if it is broken with a tool enchanted with silk touch; otherwise it will drop nothing.

Trading
Villager librarians will trade 3 to 5 glass for 1 emerald as part of their tier 3 trades.

Natural generation
Villages generate with glass pane windows.

Magenta stained glass naturally generates as windows in end cities.

A secret room containing glass can be found inside woodland mansions.

Usage
Most blocks that require placement on a solid block cannot be placed on glass or stained glass. The only exceptions are torches and redstone torches, which can be placed on top of glass, but not attached to their sides.

Glass blocks adjacent to other glass blocks are invisible when viewed through glass.