Crossword puzzle clue "silica stones"

OPAL, an amorphous variety of silica

the adhering of atoms or molecules of gases, liquids, or solutes to exposed surfaces (usually of solids)

a variety of quartz

a type of oxide, also DIOXID

to provide with a spark-producing rock

to become like a jelly

to encase in glass (a transparent material)

an amorphous variety of silica