Geology - Chapter 4

texture

The look and feel of a rock's surface, determined by the size, shape, and pattern of a rock's grains.

crystal habit

The way a mineral grows, through the regular addition of ions to its sufraces from a surrounding rock melt (magma) solution, or gas

coal

A fossil fuel that forms underground from partially decomposed plant material

hardness

A measure of how easily a mineral can be scratched

obsidian

A usually black or banded, hard volcanic glass that displays shiny, curved surfaces when fractured and is formed by rapid cooling of lava

contact metamorphism

Alteration of rock immediately adjacent to an igneous intrusion. Compositional and textural changes occurring are largely the result of high temperatures and the emanation of chemically active vapors that accompany igneous intrusions

ferromagnesian

Hornblende is designated a ferromagnesian or mafic silicate mineral because of its content of iron and magnesium

lava

Magma that reaches Earth's surface

magma

Molten rock beneath the earth's surface

continual series

The branch of Bowen's Reaction Series that comprise the plagioclase group of minerals in which reaction of early formed crystals with later liquids takes place without abrupt phase changes

discontinuous series

The branch of Bowen's Reaction Series that includes the minerals olivine, pyroxene, amphibole, and biotite. Each change in the series representing an abrupt phase change.

sillimanite

a brown, pale-green, or white neosilicate mineral with vitreous luster crystallizing in the orthohombic system; commonly occurs in slender crystals, often in fibrous aggregates

dolomite

a carbonate sedimentary rock that contains more than 50% of the mineral dolomite

aragonite

a carbonite mineral that is less common than calcite and dolomite, and has a different crystal form (CaCO3)

gneiss

a course textured metamorphic rock with well-developed and distinctive foliation

augite

a dark-colored ferromagnesian mineral which is an important member of the pyroxene family of minerals. Stumpy in shape, with good cleavage developed along two planes that are nearly at right angles.

greenstone

a dark-green metamorphic rock formed during low-grade metamorphism of basaltic rocks

chert

a dense, hard sedimentary rock or mineral composed of sum-micro-crystalline quartz. Unless colored by impurities, it's white, as opposed to flint, which is dark or black.

strata

a feature of sedimentary rocks in which the rocks occur in beds or layer

basalt

a fine-grained extrusive igneous rock composed of ferromagnesian minerals and tiny rectangular grains of plagioclase feldspars

olivine

a glassy looking iron and magnesium silicate, often with an olive green color; common mineral in dark mafic rocks

anhydrite

a granular, white, anhydrous (waterlacking) calcium sulfate

gabbro

a group of dark-colored, intrusive igneous rocks with granular texture, composed largely of basic plagioclase and clinopyroxene

feldspars

a group of silicate minerals that make up about 60% of the outer 9 miles of the Earth's crust

rhyolite

a light-colored, aphanitic volcanic rock composed largely of alkali feldspar and free silica with minor amounts of mafic minerals; the extrusive equivalent of granite

nonfoliated metamorphic rock

a metamorphic texture in which there is no discernable preferred orientation of mineral grains; marble or quartzite

density

a mineral's mass per unit volume (d=m/v)

marble

a non-foliated metamorphic rock composed of calcite or dolomite, with a fine to coursely crystalline texture; derived from limestone or dolomite

quartzite

a non-foliated metamorphic rock which is fine-grained and often sugary-textured; composed of inter-grown quartz and is very hard

hornfels

a non-foliated metamorphic rock which is very hard and fine grained; often studded with small crystals of mica and garnet having no preferred orientation; may form from shale or other fine grained rocks that are intensely heated during contact metamorphism of intrusive igneous bodies

halite

a non-silicate mineral known as rock salt; this mineral has a salty taste and cleaves to form cubes; referred to as an evaporate because it is often precipitated from bodies of water that have been subjected to intense evaporation

diorite

a phaneritic, plutonic rock with granular texture composed largely of plagioclase feldspar with smaller amounts of dark-colored minerals; used occasionally as ornamental and building stone; aslo known as black granite

pumice

a rock froth, formed by the extreme puffing up of liquid lava by expanding gases liberated from solution in the lava prior to and during solidification

sedimentary

a rock that has formed as a result of the consolidation (lithification) of accumulations of sediment

Bowen's Reaction Series

a series of minerals wherein any early-formed phase will react with the melt later in the differentiation to yield a new mineral further in the series

granite

a silica rich relatively light colored, intrusive igneous rock composed primarily of potassium feldspar, quartz, sodium plagioclase, hornblende, and mica

micas

a silicate mineral easily recognized by its perfect and conspicuous cleavage along one directional plane; two chief varieties muscovite (hydrous potassium aluminum silicate) and biotite (also contains magnesium and iron, but dark-colored)

gypsum

a soft, hydrous, calcium sulface; referred to as an evaporate because it is often precipitated from bodies of water that have been subjected to intense evaporation

foliation

a textrual feature especially characteristic of metamorphic rocks in which laminae develop by growth or realignment of minerals in parallel orientation; slate, phylite, schist, and gneiss

oolites

a textural feature of limestone with a spherical texture; limestones composed of small, round or ovate calcium carbonate bodies called ooids

micrite

a texture of limestone described by exceptionally fine grained carbonite mud

regional metamorphism

a type of metamorphic rock alteration that is really extensive and occurs under the conditions of great confinding pressures and heat accompanying deep burial and mountain building

igneous

a type of rock that forms from the cooling of molten rock at or below the surface

hornblende

a vitreous, black, or very dark green mineral; most common member of a family of minerals called amphiboles; ferromagnesian, or mafic mineral because of its iron and magnesium content; contains crystals that are long and narrow and shows two good cleavage planes parallel to the long axis which intersect each other at angles

andesite

a volcanic rock that in chemical composition is intermediate between basalt and granite

granodiorite

abundant quartz-bearing intrusive igneous rock, with plagioclase being the dominant feldspar

carbonate clasts

an individual grain, fragment, or constituent of detrital sediment or sedimentary rock produced by physical breakdown of a larger mass

plutonic igneous rocks

another term for intrusive igneous rocks (rocks that solidify under the Earth's surface)

chlorite

any of a group of greenish, platy, hydrous, monoclinic silicates of aluminum, ferrous iron, and magnesium which are closely associated with and resemble the micas

metamorphic

any rock that has been changed from previously existing rocks by the action of heat, pressure, and associated with chemical activity; the parent rock is subjected to high temps and pressure but does not melt

carbonate spar

as viewed microsopically, the clear ccrystalline carbonate that has been deposited in a carbonate rock as a cement between clasts or has developed by re crystallization of clasts

schist

consists of platy, or needle-like minerals sufficiently large to be visible to the unaided eye; tend to be segregated into distinct layers; named according to the most conspicuous mineral present; parent rock is usually shale

slate

foliated metamorphic rock with the foliation being microscopic and caused by the parallel alignment of minute flakes of silicates; derived from the metamorphism of shale

phyllite

has very fine texture, although some grains of mica, chlorite, garnet, or quartze may be visible; surfaces often develop a wrinkled aspect and are more lustrous than slate; intermediate in degree of metamorphism between slate and schist; parent rocks are commonly shale or slate

extrusive igneous rocks

igneous rocks formed from melts that have reached the Earth's surface; rocks formed from lava erupted from volcanoes or lava that has welled out of fissures

intrusive igneous rocks

igneous rocks that have formed from magma that has penetrated into other rocks and solidified before reaching the surface; very large masses of these arocks are called plutons

metamorphic index minerals

metamorphic minerals that are known to form within a specific temperature and pressure range

quartz

most important of all the silicate minerals, glassy colorless, gray, or white mineral; relatively hard and will scratch glass

mineral

naturally occurring, solid, inorganic substance having a specific chemical composition and crystal structure

silicic

rich in silica with relatively little iron and magnesium

mafic silicate mineral

rocks (or lava) dominated by dark iron and magnesium silicates, as is the oceanic crust

evaporites

sediments precipitated from a water solution as a result of evaporation of that water, includes anhydrite gypsum and halite

clay minerals

silicates of hydrogen and aluminum with additions of magnesium, iron, and potassium. Their basic structure is similar oto that of mica, but because individual flakes are extremely small, their mica-like form can only be seen with an electron microscope

ooids

spherical grains formed by precipitated of carbonate around a nucleus

porphyritic texture

texture shown due to a two-state gcooling of igneous rock; large crystals (phenocrysts) were formed slowly at depth and were then swept upward and incorporated in the lava as it hardened at the surface

clastic

texture that characterizes a rock made up of fragmental grains such as sand, silt,or parts of fossils. Conglomerates, sandstones, and siltstones are classic rocks; the individual clastic grains are termed clasts

streak

the color of a mineral in its powdered form

calcite

the predominant mineral in the carbonate rock limestone. One of the most common carbonate minerals; a polymorph of aragonite

partial melting

the process by which a rock subjected to high temperature and pressure is partly melted and the liquid component is moved to another location; results from the variations in melting points of different minerals in the other rock mass

lithification

the process by which loose sediment is converted to coherent solid rock by any of sever processes; precipitation of a cememnting material around individual grains, compaction, or crystallization

fractional crystallization

the seperation of components of a cooling magma by sequential formation of particular mineral crystals at progressively lower temperatures

vesicles

the small cavities formed when lava contains dissolved gases

cleavage

the tendency of a mineral to break along flat surfaces

metamorphism

the transformation of previously existing rocks into new types by the action of heat, pressure, and chemical solutions; usually takes place at depth in the roots of mountain chains or adjacent to large intrusive igneous bodies

luster

the way a mineral shines in reflected light

nonsilicate minerals

those minerals that do not contain the silicon-oxygen structures that characterize silicate minerals

plutons

very large masses of intrusive (or plutonic) igneous rocks

tuff

volcanic rock composed of consolidated ash