Rocks, Minerals, and Fossils

Anion

A negatively charged ion

Aphlanitic

An igneous rock texture that refers to the grains not visible to the naked eye, and therefore indicative of fast cooling

Aureole

The zone of metamorphosed rock surrounding an ingnours intrusion and showing the effects of contact metamorphism

Bar

A unit of presure equale to 10⁶ dynes/cm², approximately 1 atmosphere

Bowen’s Reaction Series

The sequence of minerals that from in the process of fractional crystalillization of a magama

Burial Metamorphism

A type of low-grade regional metamorphism affecting sediments and interlayered volcanic rocks that has lower temperatures (200^oC to 450^oC), without any infulence of orogenesis or magmatic intrusion

Cation

A positively charged ion

Color Index

A number that represents the percentage by weight or volume of dark-colored minerals in a rock

Contact Metamorphism

Metamorphism associated with the intrusion of an igneous mass. Metamorphic changes are caused principally by heat, but also by magma composition and deformation related to the intrusion. Pressures are relatively low (<3000 bars) while temperatures range from 200 °Cto 1000 °C.

Diagenesis

The physical and chemical changes undergone by sediments when compacted and lithified

Eugeosyncline

The oceanic part of a geosyncline characterized by volcanism associated with clastic sedimentation

Extrusive Rocks

Igneous rocks that have been erupted on the surface of the earth

Facies

A mappable, areally restiricted part of a rocky body that has different fossils or lithology from other contiguous beds deposited at the same time

Feldspars

The most widespread mineral group in the Earth’s crust

Felsic

A descriptive term for an igneous rock that has abundant light colored minerals

Fossil Assemblages

A group of fossils that occur at the same stratigraphic level

Geosyncline

A major downwarp in teh Earth’s crust in which sediments accumulate

Index Fossil

A fossil theat identifies and dates the strata in which it is found. It combines a wide geographic range with a narrow stratigraphic occurence.

Intrusive Rocks

Igneous rocks that have been formed within the Earth by emplacement of magam into pre-existing rock.

Mafic

A descriptive term for an igneous rock that has abundant dark colored minerals

Metamorphic Facies

A set of metamorphic mineral assemblages that have reached chemical equilibrium during metamorphism within a restricte range of temperature and pressure conditions. The concept was introduced by Eskola

Metamorphic Grade

The intensity or rank of metamorphism, measured by the amount of degree of difference between the original rock and the metamorphic rock. In general, the grade indicates the pressure-temperature environment of facies during metamorphism

Metasomatism

The process of mineral replacement wherby a new mineral of different chemical compostion grows in an old mineral. Interstitial liquids or gases must be present for solution and deposition to occur

Mineral

A naturally occuring inorganic substance, usally having an iternal crystal strucutre

Mineral Assemblages

The minerals tha compose a rock, including the different kinds and their relative abundance

Pelitic

Referring to a rock that composed of clayu or clay sized particles or derived from metamorphim of a fine-grained sediment

Phaneritic

An igneous rock texture that refers to gain sizes that are large enough to be seen with the naked eye, and indicating a slower rate of cooling

Plutonic Rocks

Igneous rocks that are generally coarsely crystalline (phaneritic) and are formed from a larger intrustion at depth.

Polymorphism

The characteristic of a mineral to exist in more than one form.

Provenance

The place of origin from which the constituent materials of a sedimentary rock or facies are derived

Regional Metamorphism

Metamorphism acting over largel areas resulting from applied presssure of 3000 to 10,000 bars and temperatures of 400^oC to 800^oC. Regional metamorphsim is also referred to as dynamothermal metamorphism

Regression

The withdrawl of the sea from land.

Rock Stratigraphic Unit

A rock unit that is characterized by a particular lithology and stratigraphic postion. A synonym is Lithiostratigraphic Unit.

Sessile

A plant of animal that is attached and cannont move

Silicates

Compoinds whose crystal structure contain SiO₄ tetrahedra, either isloalted or jointed to form groups, rings, single or double chains, sheets or three-dimensional frameworks.

Solid-Solution Series

A series of mineral;s of identical structures that contain a mixture of 2 or more elements over a range proportions

Test

The external hard part of an invertebrate

Time Stratigrphic Unit

A unti that is characterized by formation during a specific period of time and serves as a reference fro all reocks formed during the same time period. A synonym is Chronostratigraphic Unit.

Transgression

The advance of the sea onto land

Twinning

The intergrowth of two or more crystals in a symmetrical way.

Type Locality

The place were a geologic feature (such as a fossile species) was first recognized and described. It contains the type section.

Type Section

The originally described strata that contitues a stratigraphic unit to which other parts of the unit may be compared. It is preferable to describe the location where the unit attains its maximuym thickness and where the top and bottom unti are exposed

Ultramafic

An igneous rock composed of 90% or more of mafic minerals

Volcanic Rocks

Igneous rocks that are generally finely crystalline or glassy (aphanitic), resulting from volcanic action at or near the Earth’s surface (and including near-surface intrusions), either ejected explosively or extruded as Lava

Zoelites

A large group of hydroaluminosillicate minerals that are analogous in composition to the feldspars. Chief metals are Na, Ca, and K. They occur in basalt cavities, saline lake and deep sea sediments and volcanic tuff. They are used as water softeners or desiccants.

Zoning

A variation of compostion of a crystal, characteristic of feldspars. The interior or center is fomred by a high temperature phase, while the exterior opr margin is formed by a low temperature phase