The Geology of Mount Blue State Park

Glossary of Geologic Terms

Actinolite - a prismatic mineral, typically dark green, containing calcium, iron, magnesium, silicon, oxygen, and hydrogen; commonly found in calc-silicate granulite.

Apatite - a mineral, typically light green, containing calcium, phosphorus, oxygen, and fluorine; commonly found in pegmatites.

Bed - the smallest subdivision in a stratified series of rocks, marked by a more or less well-developed plane, which separates it from adjacent beds above and below.

Bedding - a collective term signifying the existence of beds.

Bedrock - the solid rock that is part of the crust of the earth, commonly overlain by soil, gravel, etc.

Beryl - a mineral, typically pale blue-green, containing beryllium, aluminum, silicon, and oxygen; found in a number of pegmatites.

Biotite - a platy mineral, typically dark brown, containing potassium, aluminum, iron, magnesium, silicon, oxygen, and hydrogen; one of the mica minerals.

Boulder - a fragment of rock, not attached to bedrock, and larger than 10 inches in diameter.

Calcareous - containing calcium carbonate.

Calcite - a mineral, typically white, containing calcium, carbon, and oxygen; the most common form of calcium carbonate.

Calc-silicate - pertaining to a rock or mineral that is predominantly composed of calcium, silicon, and oxygen.

Clay - two implications may be understood: (1) material of very fine particle size, with the individual grains less than 0.002 inch in diameter; (2) a material composed of minerals that are essentially composed of aluminum, silicon, oxygen, and hydrogen.

Coarse-grained - of large particle size.

Crystal - a polyhedral form, bounded by plane surfaces which are the outward expression of the regular arrangement of atoms which make up a mineral.

Dike - a tabular body, typically of igneous rock, which cuts across the structure of another older rock.

Diopside - a mineral, typically light green, containing calcium, magnesium, iron, silicon, and oxygen; commonly found in calc-silicate granulite.

Dip - the angle at which a planar feature, such as bedding or schistosity, is inclined from the horizontal.

Drift - any rock material transported and deposited by a glacier.

Erratic - any rock material that had been transported prior to being deposited, and thus not merely eroded out of the bedrock immediately beneath it.

Feldspar - one of the most common minerals; white, tan, buff, even pink or greenish; typically not showing a crystal form; containing potassium, sodium, calcium, aluminum, silicon, and oxygen.

Fine-grained - of small particle size

Fold - a bend or flexure in some originally planar feature, such as bedding.

Garnet - a near spherical mineral, typically pink to purplish-red, containing iron, aluminum, silicon, oxygen and commonly other components.

Glacier - a thick body of ice originating from compaction of large amounts of snow, showing evidence of movement.

Grain - the particles of discrete minerals which comprise a rock or sediment.

Granite - a particular type of igneous rock, composed essentially of the minerals quartz and potassium-rich feldspar; commonly a general term for any igneous rock containing quartz and feldspar.

Granodiorite - a particular type of igneous rock, composed essentially of the minerals quartz and sodium-rich feldspar.

Granulite - a term commonly used to indicate a metamorphic rock that does not possess a well-developed schistosity.

Gravel - a mixture of sand and pebbles.

Igneous - pertaining to a rock that has crystallized out of a melt.

Joint - a fracture which interrupts the physical continuity of a rock mass.

Joint set - a group of more or less parallel joints.

Limestone - a sedimentary rock composed chiefly of calcium carbonate.

Magma - a naturally occurring subterranean mobile mass of molten rock.

Marble - a metamorphosed limestone.

Metamorphism - the process of change of the texture and mineral content of a rock, caused by subjection of the rock to temperatures and pressures other than those under which it was originally formed.

Mica - one of a number of platy minerals, of which the most common examples in the park are muscovite and biotite.

Micaceous - containing mica.

Mineral - a naturally occurring inorganic crystalline substance.

Mud - a common term for a mixture of clay and water.

Muscovite - a platy mineral, typically colorless or slightly greenish-yellow; containing potassium, aluminum, silicon, oxygen, and hydrogen; one of the mica minerals.

Orogeny - the process of mountain building.

Outcrop - that part of bedrock that is exposed at the surface of the earth.

Pebble - a particle of rock, the dimensions of which range between 1/10 inch and 2 ½ inch in diameter.

Pegmatite - igneous rock of coarse-grain size, typically found in bodies of smaller size than the main bodies of igneous rock.

Plunge - the angle made by a linear feature, such as an axis of a fold, with the horizontal plane.

Quartz - one of the most common minerals, typically clear or slightly milky or smoky, containing silicon and oxygen.

Rock - any naturally formed aggregate or mass of mineral matter, typically consolidated and coherent.

Sand - particles of rock or mineral grains, the dimensions of which range between 0.002 inch and 1/10 inch in diameter.

Sandstone - a sedimentary rock composed of sand-sized particles. Typically quartz is the most abundant constituent.

Schist - a metamorphic rock characterized by parallel orientation of platy minerals, such as mica.

Schistosity - the prominent foliation in schist produced by parallel orientation of platy materials.

Sediment - a descriptive term for particles that had settled down from suspension in water.

Sedimentary - pertaining to a rock that had formed through consolidation of sediment.

Shale - a rock composed of consolidated mud.

Sill - a tabular body, typically of igneous rock, which is parallel to the bedding of the rock into which it had been intruded.

Sillimanite - a needle-like mineral, typically colorless, containing aluminum, silicon, and oxygen.

Strike - the direction of the intersection of an inclined plane, such as bedding or schistosity, with the horizontal plane.

Till - common term for unstratified drift.

Tourmaline - a mineral of long, thin form; typically black, but sometimes pink, green, or yellow; containing boron, aluminum, silicon, oxygen, and many other elements; commonly found in pegmatites.

Vein - tapered bodies of minerals which formed from melts or solutions.

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Last updated on January 11, 2008