Rocks

Geode (Greek γεώδης - ge-ōdēs, "earthlike") are geological secondary structures which occur in certain sedimentary and volcanic rocks.

Metamorphic rocks arise from the transformation of existing rock types, in a process called metamorphism, which means "change in form".

(For other uses of "Rock", see Rock (disambiguation).)("Rocks" and "Stone" redirect here. For other uses, see Rocks (disambiguation) and Stone (disambiguation).) In geology, rock or stone is a naturally occurring solid aggregate of one or more minerals or mineraloids.

Bauxite, an aluminium ore, is the world's main source of aluminium.

A geological fold occurs when one or a stack of originally flat and planar surfaces, such as sedimentary strata, are bent or curved as a result of permanent deformation.

Jasper, an aggregate of microgranular quartz and/or chalcedony and other mineral phases, is an opaque, impure variety of silica, usually red, yellow, brown or green in color; and rarely blue.

Serpentinite is a rock composed of one or more serpentine group minerals.

Tuff (from the Italian tufo) is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption.

Tektites (from Greek τηκτός tēktós, "molten") are gravel-size bodies composed of black, green, brown or gray natural glass formed from terrestrial debris ejected during meteorite impacts.

Charoite (K(Ca,Na)2Si4O10(OH,F)·H2O) is a rare silicate mineral, first described in 1978 and named for the Chara River.

Fulgurites (from the Latin fulgur, meaning "lightning") are classified generically as a variety of the mineraloid lechatelierite, although their absolute chemical composition is dependent on the physical and chemical properties of target material affected by the discharge of cloud-ground lightning.

Moldavite (Czech: Vltavín) is an olive-green or dull greenish vitreous substance possibly formed by a meteorite impact in southern Germany (Nördlinger Ries), which would make it one kind of tektite.

The term "molasse" refers to the sandstones, shales and conglomerates formed as terrestrial or shallow marine deposits in front of rising mountain chains.

A xenolith (Ancient Greek: "foreign rock") is a rock fragment which becomes enveloped in a larger rock during the latter's development and hardening.