Chlorite schist—a schistose rock in which chlorite is a predominant mineral; usually greenish, whence the name.
Clastic rock—formed from the débris of broken-down rocks; the same as fragmental or detrital rock.
Clay—a term commonly applied to any soft, unctuous, adhesive deposit, but in strict use confined to material composed of aluminum silicate; many so-called clays are chiefly silicious silts or loams.
Clay ironstone—a clayey rock heavily charged with iron oxide, usually limonite; commonly in concretionary form.
Clinkstone—a name applied to phonolite because of its metallic clinking sound when struck; composed of orthoclase, with nephelite and one or more of the ferromagnesian minerals as accessories.
Chert—an impure flint, usually of light color, occurring abundantly in concretionary form as nodules in certain limestones.
Coal—a carbonaceous deposit formed from the remains of plants by partial decomposition.
Concretions—aggregates of rounded outlines formed about a nucleus; the material is various: clay, iron ore, calcite, silica, etc.
Conglomerate (pudding-stone)—a rock formed from rounded pebbles, consolidated gravel.
Coquina—a rock formed almost wholly of small and broken shells; especially applied to a shell limestone of Florida.