quartz - a hard glossy mineral consisting of silicon dioxide in crystal form; present in most rocks (especially sandstone and granite); yellow sand is quartz with iron oxide impurities

agate - an impure form of quartz consisting of banded chalcedony; used as a gemstone and for making mortars and pestles

bloodstone, heliotrope - green chalcedony with red spots that resemble blood

carnelian, cornelian - a translucent red or orange variety of chalcedony

chrysoprase - a green variety of chalcedony valued as a gemstone

onyx - a chalcedony with alternating black and white bands; used in making cameos

plasma - a green slightly translucent variety of chalcedony used as a gemstone

sard, sardius, sardine - a deep orange-red variety of chalcedony

transparent gem - a gemstone having the property of transmitting light without serious diffusion