agate is a common stone formation, consisting of chalcedony and quartz as its main components, consisting of a wide variety of colors. agates are primarily formed within volcanic and metamorphic stones.
opal is a hydrated amorphous form of silica. because of its amorphous character, it is classed as a mineraloid, unlike crystalline forms of silica, which are classify as minerals.
emerald is a gemstone and a type of the mineral beryl colored green by trace amounts of chromium and sometimes vanadium. emerald in antiquity were mined in Egypt at locations on Mount Smaragdus since 1500 BCE.
