Glauconite—a greenish mineral commonly formed in marine environments and essentially a hydrous silicate of iron and potassium.
Goniatite—an ammonoid [cephalopod] with [suture] composed of smooth saddles and simple angular lobes; member of subclass Ammonoidea.
Graptolite—an extinct, marine, [colonial] organism with [chitinous] hard parts; believed to belong to subphylum Hemichordata of [phylum] Chordata.
Guide fossil—see [Fossil].
Habitat—the physical environment in which an organism lives.
Hinge-line—in brachiopods, the edge of the shell where the two valves articulate; in pelecypods, the [dorsal] margin of the [valve] which is in continual contact with the opposite valve.
Igneous rock—rocks which have solidified from lava or molten [rock] called magma.
Index fossil—see [Fossil].
Inequivalved—opposite valves unlike in shape or size, or both.
Jurassic—second oldest [period] of the [Mesozoic]; follows the [Triassic], precedes the [Cretaceous].