Caldera. A large basin-shaped depression caused by explosion or collapse around a volcanic center.
Cassiterite. A heavy, brown to brownish black mineral composed of tin and oxygen (SnO₂) that is an ore of tin.
Cephalopod. A marine [mollusk] with a head surrounded by tentacles. Squids and octupuses belong to this group, as do [fossil] forms having straight or coiled shells divided into numerous interior chambers.
Chalcopyrite. A reddish-gold colored ore of copper (CuFeS₂).
Cirque. A deep, steep-walled recess in a mountain, caused by glacial erosion at the head of a valley.
Concretion. A nodular or irregular concentration of minerals such as calcite or limonite, formed by precipitation of the mineral from groundwater around a nucleus.
Conglomerate. A rock containing coarse fragments of an older rock, usually as rounded water-worn stones or pebbles.
Conodont. One of a group of tiny dark brown tooth-like [fossils] thought to be dermal or dental parts of some extinct group of fish.
Diatreme. A volcanic vent or pipe drilled through rocks by the explosive energy of gas-charged molten rock, now containing igneous rock and often altered or unaltered fragments of the surrounding rock.
Dike. A vertical or nearly vertical sheet of igneous rock which cuts across the structure of adjacent rocks.