Geology: Sedimentary Rocks, Metamorphic Rocks, the Rock Cycle, and Weathering

Flashcards summarizing detrital and chemical sedimentary rocks, metamorphic textures and classifications, the rock cycle, and weathering, erosion, and mass wasting processes.

How are detrital sedimentary rocks classified by grain size and grain shape?

Coarse grain size with angular grains is breccia; coarse grain size with rounded grains is conglomerate; medium grain size is sandstone; fine grain size is siltstone; and very fine grain size is shale.

What are evaporites and how do they form?

Evaporites are abiotic chemical sedimentary rocks formed when mineral-laden water evaporates and leaves mineral deposits behind, such as rock salt (halite) and rock gypsum (gypsum).

What are the descriptions for limestone, fossiliferous limestone, chalk, and coquina?

Limestone is abiotic calcite; fossiliferous limestone consists of cemented shells, corals, and fragments; chalk is calcitic plankton shells; and coquina consists of loosely cemented calcitic shells and fragments.

What composition forms chert/flint, and what chemical sedimentary rock forms from compressed plant matter?

Chert/flint is composed of siliceous plankton shells and abiotic silica. Compressed and lithified plant matter forms coal.

In what two settings does the metamorphism of rocks primarily occur?

Metamorphism occurs in a baked zone where magma bodies heat surrounding rocks underground, and during mountain building generated by plate tectonic activity under immense heat and pressure.

How does low-grade metamorphism differ from high-grade metamorphism?

Low-grade metamorphic rocks typically look much like their parent rock, whereas high-grade metamorphism alters a rock's appearance significantly so that it may bear little resemblance to its parent rock.

What distinguishes foliated metamorphic rocks from non-foliated metamorphic rocks?

Foliated metamorphic rocks develop a layered or banded appearance due to crystal alignment under high temperature and pressure, whereas non-foliated metamorphic rocks do not form layers or bands.

What are the textures and descriptions of slate, phyllite, schist, and gneiss?

Slate is foliated & very fine grained (looks like shale); phyllite is foliated & fine grained (looks like shiny, wavy slate); schist is foliated & medium to coarse grained (typically scaly or flaky); and gneiss is foliated & medium to coarse grained (has light and dark banding).

How can non-foliated marble and quartzite be distinguished by composition and chemical/physical properties?

Marble is composed of calcite, effervesces with acid, and will not scratch glass; quartzite is composed of quartz, does not effervesce with acid, but will scratch glass.

What is the geological concept of the rock cycle?

The rock cycle illustrates that all types of rocks are continually recycled, as any type of rock can potentially be turned into another type of rock.

What key steps convert an igneous rock into sediment, then into a sedimentary rock, a metamorphic rock, and back to magma/igneous rock?

Igneous rock undergoes weathering to become sediment, lithification to become sedimentary rock, heat and pressure to become metamorphic rock, melting to become magma/lava, and cooling/crystallization to form new igneous rock.

How are weathering, erosion, and mass wasting defined and distinguished?

Weathering is the mechanical and/or chemical breakdown of rocks; erosion is the movement of soil, sediment, or rock by wind, water, or ice; and mass wasting is the movement of soil, sediment, or rock down slope due to gravity.

What three mineral crystals are identified in the weathered granite example, and what are their visual descriptions?

Quartz (colorless and translucent), hornblende (black), and feldspar (light-colored and opaque).

How does rainwater act as both a chemical and mechanical agent of weathering?

Rainwater acts chemically by slowly dissolving some minerals, and mechanically through repeated impacts of raindrops that weaken soft rocks (e.g., turning sandstone back into sand).