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Transcript of Rocks
- naturally occuring solid materials which contains one or more minerals ( combination of oxygen, silicon, aluminum, iron, calcium, sodium, potassium and magnesium )
- from Latin word "Ignis'' ( fire )
- produce deep underground by the cooling and hardening of magma
- molten rock produced in upper part of mantle or lowest area of crust
- less dense than the surrounding rocks which cause it to rise
When magma reaches the surface, it is called lava. The lava that reaches the earth's surface will harden and become igneous rock.
Extrusive Igneous Rock
- formed when lava reaches the Earth's surface
- glassy or finely crystalline in texture
Intrusive or Plutonic Rock
- when magma solidifies; does not reach the Earth's surface
-has coarser texture with large masses of crystal grain of varying sizes
- forms batoliths, laccoliths, sills and dikes
Sills- similar to dikes except that the magma wedges itself horizontalt between sedimentary rock layers over a wide area;
- thin sheet
Dikes - form when cracks or fissures is filled with magma
Laccoliths- from magma that intruded between layers of sedimentary rocks
Batholiths - parent source; great size and extend downward definitely; form the roots of mountain ranges and bases of continents
Common Igneous Rocks
- from lava;
- usually light grey, pink, purple, or yellow color
- composed of same minerals as granite
- the difference is that the most of the crystals are so small that they can't be seen with the naked eye, whereas in the granite are big enough to see ( >0.5 mm).
Granite ( gran-it)
- forms when magma cools in the deep of the crust ( 2-50 km ) like batholiths.
- forms in areas of convergent tectonic platesin which coarse-grained of igneous rock (quartzfeldspar, and mica found)
-light colored, can be dark pink
-has light gray or pink with small dark spots
Andesite ( ann-da-site)
- extrusive igneous fine-grained,rock
-contains some minerals common to to ryolite and basalt
-look like basalt to unaided(naked) eye; but usually less dark or greenish in color
- Andesite magma is viscous(thick and sticky) and formsthick lava flows
Diorite ( die-a-rite)
- is a plutonic rock from magma.
- occurs in large amounts in peak of the mountains places like Scotland, mid Europe and Norway
Basalt ( basalt )
- extrusive igneous fine-grained rock with the same minerals as is intrusive like gabbro
-looks like black, or grey
-formed in areas where tectonic plates move apart ( diverge )
Gabbro ( gab-row )
- coarse-grained, intrusive igneous rock; usually dark or greenish
-forms deeper in Earth's crust than basalt; occurs like batholiths and laccoliths
Peridotite ( per-rid-o-tite)
- plutonic coarse-grained rock that composed of :
*Olivine - common mineral in the Earth's subsurface but weathers quickly on the surface
*Amphibole - dark-colored, needlelike crystals
*Pyroxene - important rock-forming inosilicate minerals found in many Igneous and metamorphic rocks
Obsidian ( ob-sid-ian )
-fomed when rhyolite magma is cooled rapidly and contact surfaces of intusions; jet black in color, has a glossy luster
Pumice ( pum-miss )
- fragments of solidified magma foam that throwm into air during volcanic eruption that may get carried very far from the source area
Scoria ( score-ee-a)
- hardened lava that has retained the vesicles produced by the escape of gases
- formed from broken pieces of rocks
-larger sediments fall out first and lightest sediments fall out last
Deposition - laying down of rock-forming material by natural agent ( water, ice, gravity and wind )
Types of Sedimentay Rocks
Sedimentary rocks are formed from :
1. Lithification of Sediments
- process in which sediments compact under pressure, and gradually become solid rock.
2. Precipitation from solution
3. Consolidation of the remains of plants or animals
-is a process by which soils decrease in volume
These are called clastic, chemical, and organic rocks resperctively.
A. Clastic Sedimentary Rocks
- formed from cemented sediment grains that are fragments of preexisting rocks
1. Conglomerate ( con-glom-erate )
- mostly gravel;particles vary largely in size
2. Sandstone ( sand-stone )
- sand-sized grains of rock after shale and sandstone; forms in ariety of environments and contains important clues about the past
- consist of silt and clay-sized particles(can only be identified with great magnification)
B. Chemical Sedimentary Rocks
- rocks deposited by precipitation of minerals from solution
-formation of rock saltas seawater evaporates
- can form by precipitation of calcite within coral reef by corals and algae
- formed from material that is carried in solution to lakes and seas
-most abundant chemical sedimentary rock
-composed mostly of mineral calcite
-calcium carbonate is locked into the fossil shells and skeletons of marine organisms
Two major types : biochemical and inorganic limestone
The chemical formation of limestone occurs in caves. Water can enter a cave through fractures or pore spaces in the cave’s ceiling. When this happens, it might hang on the ceiling or drop directly to its floor. When the drop hangs onto the ceiling and evaporates, it leaves behind the dissolved calcium carbonate that it carried. As the water continuously enters the cave, more and more calcium carbonate is collected on the same spot. Eventually, this will cause CaCO3 to collect enough that limestone is formed. The proper name for this cave formation is stalactite. There is also another way that limestone forms chemically, and that is when the drop of water falls to the floor. The formation of a stalagmite (basically an upside down stalactite) happens when the water that sits on the floor dissolves. The only difference in both chemical formations is where the water evaporates and leaves the CaCO3
C. Organic Sedimentary Rocks
- rocks that accumulate from the remains of organism
Coal is an example; it forms from the compaction of plant remains
- occurs when any previously existing rock(parent rock) is burried in the Earth under layers of other rock
- the deeper, the hotter and higher pressure
The word "metamorphic" comes from the Greek word "to change form"
Three Main Agents of Metamorphism
- can cause layers of sediments being buried deeper under the surface of the Earth
- the deeper the layers, the hotter the temperature
- the great weight of these layers also causes an increase in pressure which cause an increase in temperature
It can be caused by:
1. The huge of overlying layers of sediments.
2. Stresses caused by plates colliding in the process of mountain building.
3. Stresses caused by plates sliding past each other, such as the shearing stressesnat the San Andreas fault zone in California.
It happens when extreme pressure cause very hot fluids and vapors fill the pores of existing rocks.
Common Metamorphic Rocks
- very fine grained, foliated ( repetitive layered ) rock
- not usually visibly foliated
- considered as low-grade metamorphism of shale that may be a form of metamorphosed volcanic ash
b. Phyllite ( phy-lite )
-is both slate and schist form of meatamorphic rocks scale.
-looks like slate, but it's glossy sheen gives it away
- strongly foliated and can be seen easilyinto thin flakes or slabs.
- parent rock is shale, but the metamorphism is much greater
d. Gneiss ( nice )
- contain mostly elongated and granular
-easily identifiable by the segregations of light and dark minerals giving it banded texture and bands of light and dark
- non-foliated, coarse,crystalline rock from limestone
- pink, grey,green or black
f. Quartzite ( kwarts-ite )
- hard, non-foliated, metamorphic rock usually from quartz-rich sandstone
- bonds of quartz grains are so strong that when quartzite is broken, it will break only along the quartz grains
- usually white, but iron oxide may produce reddish, pinkish, purple colors