For definition and description of rocks most commonly found in Central Park, see "Types of Rocks" in the introduction.

AMPHIBOLITE (am-PHIB-o-lite): a dark greenish to black fine-grained metamorphic rock. In Central Park, it is characterized by narrow white layers. Outcrops are usually blocky and smooth to the touch.

DIKE: an intrusion that cuts across the layering of the host rock.

ERRATIC: a large boulder or mass of alien rock usually transported from its original site by glacial ice.

GARNET: any of various crystalline silicates containing aluminum and other elements and ranging in color from green and yellow to brown, red or violet. The red garnet occurs in Central Park.

GRANITIZATION: transformation of existing rock into granite by means of beat, pressure and chemically active fluids and/or gases.

IGNEOUS ROCK: rock formed by cooling and solidification of molten material called magma.

INTRUSION: molten rock material forcibly injected into existing rock and cooled at depth.

MAGMA: rock material heated to plastic or semifluid consistency. Generated in deep underground reservoirs, magma can be discharged onto the surface by volcanic action or injected into fissures in the Earth's crust.

METAMORPHIC ROCK: one that has been transformed in texture and/or composition by a combination of thermal, physical and chemical forces.

SEDIMENTARY ROCK: rock formed by deposition and consolidation of solid particles carried by air or water, or by precipitation of dissolved chemicals.

SILL: an intrusion that conforms to the layering of the host rock.

STRATUM: in a sedimentary rock, a single layer of uniform composition and texture.

XENOLITH (ZEN-o-lith by the dictionary; ZEEN-o-lith in popular usage by geologists): a fragment of bedrock torn off by forceful entry of magma and enclosed in the solidified intrusion.