A brief introduction to minerals, rocks and the rock cycle

Transcription

1 and Rocks A brief introduction to minerals, rocks and the rock cycle rock minerals collection of one or more minerals mineral A collection of one or more types of atoms : the building blocks of rocks : the building blocks of rocks Definition of a mineral Definition of a rock -> To be considered a mineral, it must: 1. Occur naturally 2. Be inorganic 3. Be a solid 4. Possess an orderly internal structure 5. Have a definite chemical composition -> different from that of a mineral. A rock: 1) is solid 2) contains a mixture of one or more minerals 3) May contain a non-mineral 4) occurs naturally as part of our planet

2 : the building blocks of rocks The composition of minerals Rocks and minerals Some rocks composed entirely of one mineral limestone (calcite) Most rocks have more than one kind of mineral granite Some rocks contain non-mineral matter coal (has organic debris) obsidian (volcanic glassy rock -> not crystalline) Granite & constituent minerals Over 4000 minerals: only few dozen are abundant, making up most rocks of Earth s crust => rock-forming minerals Percent of elements by WEIGHT Only 8 elements make up most of crust s minerals & represent over 98% of the continental crust The two most abundant elements: Silicon (Si) Oxygen (O) Average composition of the continental crust

3 112 known elements Only 92 occur naturally The composition of minerals Atomic structure Mineral groups The silicates Silicon and Oxygen combine to form the most common mineral group, the silicates. Every silicate mineral contains the elements silicon (Si) oxygen (O) Nearly every silicate mineral combines with one or more additional elements to achieve electrical neutrality 1) Mineral groups The silicates The fundamental building block of all silicates is the silicon-oxygen tetrahedron Two different views of this arrangement: silicon atom oxygen atoms 1) Mineral groups Light colored (crust, esp. continental crust) Non-ferromagnesian (felsic) silicates Feldspar (Si, O, Al, K, Na, Ca) - mostly white or pink 50% of earth s crust! Quartz (SiO 2 =silica) - commonly transparent silicate that consists only of silicon and oxygen second most abundant in crust! Muscovite The silicates Remember: Silicates are the most abundant mineral group with the silicate ion as basic building block. (Si, O, Al, K, H) most common mica cleavage in sheets, glass in Middle ages sparkle in rocks, mica flakes in sand

4 Mineral groups The silicates Remember: Silicates are the most abundant mineral group with the silicate ion as basic building block. Dark colored (mantle, basalt, continental crust) Ferromagnesian (mafic) are dark silicates, contain ions of iron and/or magnesium) Mineral groups Important Nonsilicate 2- Carbonates (CO 3 ) = carbonate ion Calcite (CaCO 3 ) Dolomite (CaMg(CO 3 ) 2 Forms limestone Calcium/magnesium Carbonate, forms dolostone found together in sedimentary rock limestone, Main ingredient to cement, roads & building stones Olivine black to olive green, in basalt Pyroxene important component of earth s mantle Hornblende important component of continental rock Biotite iron rich mica, component of continental rock Mineral groups Important Nonsilicate Halides Halite (NaCl) -> common table salt Sulfates Gypsum (CaSO4-H2O) -> calcium sulfate + water, main ingredient of plaster & other building materials Oxides Hematite (Fe2O3) -> mined for iron, steel Ice (H2O) -> solid form of water Rocks Three major types of rock

5 Rock cycle and the three basic rock groups. The rock cycle is an interaction between Climate and Plate Tectonic System From Tarbuck, Lutgens: Earth From Press, Siever: Understanding Earth, 4 th edition Rocks Igneous rocks Extrusive-Intrusive Extrusive rocks are formed at the surface from lava, rapidly cooling, small crystals, finegrained texture. Sedimentary rocks How to make a sedimentary rock. Diagenesis Any physical and chemical change that happens to the sediments or the sedimentary rock Intrusive rocks are formed from magma in Earth s crust, slow cooling, large crystals, coarse texture.

6 How to make a metamorphic rock. Recall: 3 fundamental rock types metamorphism Lit. change form Rocks Metamorphic rocks Metamorphic rocks form under 4 main conditions: Transform: Igneous Sedimentary into: process Metamorphic Metamorphic occurs deep Contact Ultra high P Regional high P High P, Low T TODAY: Plate Tectonics (Part I) Intro: Chemical and physical structure of Earth 1) The plate tectonic system 2) A theory is born 3) Early evidence for continental drift Earth s layer by chemical properties Earth s s layering by chemical properties Crust Mantle Core Read Chapter 3!

7 Earth s layer by physical properties Lithosphere and asthenosphere Lithosphere: Crust and uppermost mantle. Broken into 12 plates. Brittle, rigid km Asthenosphere: Lower portion of upper mantle, down to 660km Soft, deformable, small amount of melting ) The plate tectonic system 1) The plate tectonic system Convection Fig The lithosphere is the outer rigid shell of earth, about 100km thick. It is broken into a dozen large plates that move on the plastic asthenosphere (lower part of the upper mantle) 2. The lithosphere is created at mid-ocean spreading centers and subducts when converging with another plate. 3. The driving force of this movement are convection currents in the asthenosphere.

8 PLATE 1) The plate 1) Overview tectonic system TECTONICS Compare with Fig. 3-14