Agate

Agate /ˈæɡət/ is a common rock formation, consisting of silica, chalcedony and quartz as its primary components,[1] the formation consists of a wide variety of colours and grain size. Agates are primarily formed within volcanic rocks and metamorphic rocks. These stone have been seen to have dated back as far as Ancient Greece, however with their mediocre durability, their every day uses are most commonly as decorations or jewelry. https://en.wikipedia.org/wiki/Agate