Exam 2 Rocks
Nonconformity
A type of unconformity in which layered sedimentary rocks lie on an erosion surface cut into igneous or metamorphic rocks
how different metamorphic grades affect the rocks' mineralogy.
A geologist can identify different grades of metamorphism in the field based on the presence of specific minerals, called index minerals.certain minerals have limited pressure and temperature range. These index minerals record metamorphic grade. When these index minerals are identified, one can get a general idea of the metamorphic history of the rock.
soil profile
All the vertical layers or horizons that make up a soil in a particular place
hydrothermal metamorphism
Chemical alterations that occur as hot, ion-rich water circulates through fractures in rock.
inclusions
Chemical substances such as stored nutrients or cell products
relative dates
Dates expressed relative to one another (for instance, earlier, later, more recent) instead of in absolute terms.
fossil succession
Fossil organisms succeed one another in a definite and determinable order, and any time period can be recognized by its fossil content.
difference between chemical and mechanical weathering
Mechanical weathering is the physical breakdown of rock into smaller pieces. Chemical weathering is the breakdown of rock by chemical processes.
original horizontality
Principle stating that sedimentary rocks are deposited in horizontal or nearly horizontal layers.
Lateral Continuity
Principle that states that an original sedimentary layer extends laterally until it tapers or thins at its edges.
Organic Sedimentary Rock
Sedimentary rock that forms from the remains of plants or animalsexamples: coal, organic limestone
clastic sedimentary rock
Sedimentary rock that forms when fragments of preexisting rocks are compacted or cemented together.
Chemical Sedimentary Rock
Sedimentary rock that forms when minerals precipitate (a solid forms from a liquid solution) from a solution- forms from solution of dissolved minerals and waterExample: halite
Sorting
Sorting is a description of the distribution of clast sizes present: a well-sorted sediment is composed of clasts that mainly fall in one class on the Wentworth scale (e.g. medium sand); a poorly sorted deposit contains a wide range of clast sizes.
Evaporation
The change of a substance from a liquid to a gas
fissility
The property of splitting easily into thin layers along closely spaced, parallel surfaces, such as bedding planes in shale.
half lives
The time it takes for half the amount of a radioactive substance to disappear as a result of radioactive decay.
four types of weathering
There are four main types of mechanical weathering: frost wedging in which rocks are broken by water freezing within cracks, salt crystal growth in which rocks are broken by salt freezing within cracks, sheeting in which rocks dome upward and peel off, and biological activity in which living things such as tree roots break rocks apart.
difference between erosion and weathering
Weathering is when rocks are broken down (chemically or mechanically) and erosion is when sediment is carried away.
index fossil
a fossil known to have lived in a particular geologic age that can be used to date the rock layer in which it is found
Superposition
a principle that states that younger rocks lie above older rocks if the layers have not been disturbed
seidmentary rock
a rock that forms from compressed or cemented layers of sediment
Disconformity
a type of unconformity in which the sedimentary layers above and below the unconformity are parallel
contact metamorphism
changes in rock caused by the heat from a nearby magma body
cementation
comes from the water that exists in the formation so growth of cement and reduction of water leads to lithification
cross cutting
cut into action that is happening simultaneously
subduction zone metamorphism
high pressure, low temperature metamorphism that occurs where sediments are carried to great depths by a subducting plate
impact metamorphism
metamorphism that occurs when meteorites strike Earth's surface
how metamorphic rocks are created from parent rocks
parent rock is the rock type that a metamorphic rock was before it was subjected to metamorphic conditions.
numerical date
specify the actual number of years that passed since an event, whereas relative dates determine the order of events in relation to one another.
Compaction
the process by which sediments are pressed together under their own weight
radiometric dating
the process of measuring the absolute age of geologic material by measuring the concentrations of radioactive isotopes and their decay products
lithification
the process of turning into rock
angular unconformity
tilted rocks are overlain by flat-lying rocks