Epoch—a unit of geologic time that is a subdivision of a [period].
Era—a major division of geologic time, which consists of several [periods].
Extrusive rocks—[igneous rocks] formed from [magma] that was extruded on the earth’s surface.
Fault—a break in the rocks or strata of the earth’s crust along which movement or slippage has taken place.
Fluid—a substance made up of particles that can move freely about; it can be a liquid or a gas.
Formation—rocks or strata that are recognized and mapped as a unit.
Fracture—the kind of surface obtained if a mineral is broken in a different direction from that of the [cleavage] or [parting]. Commonly, [fracture] surfaces are rough, uneven, or curved, whereas cleavage surfaces are smooth.
Geologic map (areal)—shows the extent and distribution of [formations] exposed at the earth’s surface.
Granular—the texture of a rock or mineral that is made up of visible grains. If all the grains are about the same size, the term equigranular is used.
Granule—a rock or mineral fragment that has a diameter of from 2 to 4 millimeters (about ⁸/₁₀₀ to ¹⁵/₁₀₀ of an inch).