Chapter 5: Rocks, minerals, and fossils

Aphanitic

An ingenious rock texture that refers to the grains not visible to the naked eye, and indicates fast cooling

Aureole

The zone of metamorphosed rock surrounding an igneous intrusive and showing the effects of contact metamorphism

Bar

A unit of pressure equal to 10^6 dynes/cm², or approximately 1 atmosphere

Burial metamorphism

A type of low-grade regional metamorphism affecting sediments and interlayers volcanic rocks that has lower temperatures (200-450˚C), without any influence of orogenesis or magmatic intrusion.

Cation

A positively charged ion

Anion

A negatively charged ion

Color index

a number that represents the percent by weight or volume of dark colored minerals in a rock

Contact metamorphism

Metamorphism associated with the intrusion of an igneous mass. Matamorphic 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 200-1000C

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

Facies

A mappable, really restricted part of a rock body that has different fossils or lithology from other contiguous beds deposited at the same time

Feldspars

Most widely spread group of minerals in the crust

Felsic

Descriptive term for igneous rock that has an abundance of light colored minerals

Geosyncline

Major downwarp in the Earth’s crust in which sediments accumulate

metamorphic grade

Intensity or rank of metamorphism, measured by amount or degree of difference between the original rock and the metamorphic rock. Indicates pressure-temperature environment during metamorphism

Pelitic

Referring to a rock that is composed of clay or clay-sized particles, or derived from metamorphism of fine-grained sediment

Phaneritic

Igneous rock texture that refers to grain sized that are large enough to be seen with naked eye, indicating slower rate of cooling

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.

Regression

Withdrawal of sea from the land

Sessile

A plant or animal that is attached and cannot move

Solid-solution series

A series of minerals of identical structures that contain a mixture of two or more elements over a range of proportions

Transgression

the advance of sea onto land

Twinning

the intergrowth of two or more crystals in a symmetrical way

Type locality

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

Type section

The originally described strata that constitutes 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 maximum thickness and where the top and bottom of the unit are exposed

Ultramafic

>90% mafic minerals

Zeolites

Large group of hydroaluminosilicate minerals that are analogous in composition to the feldspars. Chief metals are Na, Ca, and K, occurring in basalt cavities saline lake and deep sea sediments, and volcanic tuffs. Used as water softeners

Zoning

A variation of composition of a crystal, characteristic of feldspars. The interior is formed by high temperature phase, while the exterior is formed by lower temperature