EARTHSCI - Rocks and the Rock Cycle

ROCK

a naturally-occurring, coherent aggregate of minerals or solid materials

ROCK CYCLE

a model that describes all the processes by which rocks are formed, modified, transported, decomposed, melted and reformed.

IGNEOUS ROCKS

- formed from the cooling and solidification of magma or lava.

- derived from Latin igneus, which means "fiery" or "on fire"

crystalline textures:

- intrusive or plutonic

- extrusive or volcanic

- pyroclastic

CLASSIFICATION OF IGNEOUS ROCKS

intrusive or plutonic

- Below the surface, slowly cooling magma

- the resulting texture is phaneritic ( phaneros - Greek word meaning "visible").

- In cases when minerals crystallize very slowly at depth, the resulting texture is pegmatitic texture, one that is composed of very large crystals.

extrusive or volcanic

- On the surface, from rapidly cooling lava

- exhibit aphanitic textures (aphaneros- Greek word meaning "invisible")

- glassy -special volcanic texture, when lava is expelled underwater

- vesicular texture -a result of gases escaping while the volcanic rock is being formed.

- porphyritic texture -volcanic activity extrudes the partially crystallized magma onto the surface

pyroclastic

- On the surface, from the consolidation of particles erupted by explosive volcanic activity

- from the Greek pyro which means "fire" and klastos which means "shattered"

- result of the lithification of erupted volcanic material

- these types of rocks are distinguished from each other by size of its particle components.

Felsic

Intermediate

Mafic or Ultramafic

COLOR INDEX OF IGNEOUS ROCKS

Felsic

rich in silica (light colors- light, gray, tan, pink)

Intermediate

Intermediate color (gray or consisting of equal parts of light and dark mineral)

Mafic or Ultramafic

poor in silica but rich in magnesium (dark colors- black and brown)

SEDIMENTARY ROCKS

- the products of lithification of particles by the weathering of other pre-existing rocks.

Sediments- derived from the Latin sedentarius which means "sitting"

Clastic

Chemical/ Crystalline/ Nonclastic

Bioclastic

FORMATION OF SEDIMENTARY ROCKS

Clastic

From the cementation of sediments that have been deposited, buried and compacted over a long period of time

Chemical/ Crystalline/ Nonclastic

From the precipitation of minerals from ions in solution

Bioclastic

From the compaction and concentration of plant and/or animal remains

Clay or Silt- less than 1/16 mm (not visible to naked eye)

Sand grains- between 1/16 mm - 2mm

Gravel- greater than 2mm

TYPES OF CLASTIC SEDIMENTARY ROCKS

limestone, dolostone, halite, calcite, gypsum

TYPES OF CRYSTALLINE SEDIMENTARY ROCKS

coquina, bituminous coal, chalk

TYPES OF BIOCLASTIC SEDIMENTARY ROCKS

METAMORPHIC ROCKS

form when pre-existing or parent rocks are altered by heat, pressure, and the chemical activity of fluids

Metamorphism

change in form

Regional metamorphism

Contact metamorphisn

FORMATION OF METAMORPHIC ROCKS

Regional metamorphism

involves tectonic processes; the dominant altering factor is pressure (foliated)

Contact metamorphism

from direct contact between an older rock material and an intruding body of magma; the dominant altering factor is heat (nonfoliated)

1. Foliated/ Platy- Latin folium which means leaf

- slaty (microscopic); phyllitic (barely visible); schistose (visible); gneissic (visible and elongated).

2. Nonfoliated/ Crystalline

- marble, quartzite, anthracite coal

CLASSIFICATION OF METAMORPHIC ROCKS