L3 - Rocks and Minerals.pdf

Rocks and Minerals Rocks Earth is a solid rock to a depth of 2,900 kilometers, where mantle meets the liquid outer core. A rock is a naturally occurring solid aggregate of one or more minerals. The aggregate minerals forming the rocks are held together by chemical bonds. Grains can be di...

Rocks and Minerals Rocks Earth is a solid rock to a depth of 2,900 kilometers, where mantle meets the liquid outer core. A rock is a naturally occurring solid aggregate of one or more minerals. The aggregate minerals forming the rocks are held together by chemical bonds. Grains can be different in color, texture, and sizes. Geologists then group rocks into three categories based on how the rocks form: igneous sedimentary and metamorphic rock. Petrology is the scientific study of rocks. Petrologists classify rocks based on how they were formed.  Igneous Rocks formed from hardening and crystallization of magma or molten material that originates deep within the earth. Two types of igneous rock: A. Extrusive/Volcanic rock - forms when magma makes its way to Earth’s surface as lava and then cools. The crystals are very small (fine grained) since the cooling process is fast. B. Intrusive/Plutonic - It cools slowly beneath the Earth surface and are created by magma. The intrusive igneous rocks have very large crystals (coarse grained).  Igneous Rocks Igneous rocks are classified based on: 1. Composition FELSIC - light in color; feldspar and silicates MAFIC - dark in color; made up of magnesium and iron INTERMEDIATE – between mafic and felsic ULTRAMAFIC - very dark color  Igneous Rocks Igneous rocks are classified based on: 2. Texture- overall appearance of rock Aphanitic - fine grained Phaneritic- coarse grained Porphyritic- large crystals with small crystals Glassy- non-ordered solid from rapid quenching Pyroclastic- composite of ejected fragments Examples: Obsidian, pumice, basalt, granite, diorite, gabbro  Metamorphic Rocks Metamorphic - forms from pre- existing rocks: either metamorphic, igneous, sedimentary Examples: Quartzite, marble, slate, phyllite Metamorphism - transformation of one rock type into another.  Metamorphic Rocks Usually found deep within the earth and/or where tectonic plates meet  Metamorphic Rocks 2 Types of Metamorphism 1. Regional - due to changes in pressure and temperature over large region of the crust 2. Contact - mainly by heat due to contact with magma Regional Metamorphism Regional metamorphism occurs when rocks are buried deep in the crust. This is commonly associated with convergent plate boundaries and the formation of mountain ranges. Because burial to 10 km to 20 km is required, the areas affected tend to be large. Contact Metamorphism Contact metamorphism occurs to solid rock next to an igneous intrusion and is caused by the heat from the nearby body of magma. Because contact metamorphism is not caused by changes in pressure or by differential stress, contact metamorphic rocks do not become foliated.  Metamorphic Rocks Classification: a. Texture - refers to the size arrangement ad grains within the rock. b. Foliation - any planar arrangement of mineral grains or structural features within the rock. Foliated - appeared banded or layered, contains crystals Example: mica Non-foliated - made up of only few minerals  Sedimentary Rocks Sedimentary rocks provide information about surface conditions that existed in the Earth’s past. Particles of sand, shells, pebbles, and other fragments of materials called sediments, accumulate in layers and over long period of time harden into rocks. Compaction-due to increase of pressure of layered sediments it bind together to form the sedimentary rocks.  Sedimentary Rocks Three types of sedimentary rocks a. Clastic - formed from accumulation of clasts: little pieces of broken rocks and shells. Examples: conglomerate, breccia, sandstone, shale b. Chemical - formed when dissolved minerals precipitate from a solution. Example: Halite - formed when a body of seawater becomes closed off and evaporates. c. Organic - rocks formed from the accumulation of animal debris Example: Coal - composed of organic matter in the form of plants fragments. Minerals The building blocks of rocks are minerals. Mineralogists use the criteria to determine whether a material is classified as a mineral or not. (Distribute the DEAR material)  Characteristics of Minerals 1. Naturally occurring - a product of Earth’s natural processes 2. Inorganic - it must be product of Earth’s physical processes. 3. Homogeneous solid - minerals should have definite volume and rigid shape 4. Definite chemical composition - represented by a chemical formula 5. Orderly crystalline structure - atoms of minerals are arranged in an orderly and repeating pattern  Properties of Minerals a. Color - mineral’s color may change depending on the surface. b. Streak - color of mineral in powdered form. c. Hardness - minerals resistance to scratching  Properties of Minerals d. Cleavage - mineral’s resistance to being broken and fracture e. Crystalline structure is the internal structure of atoms f. Diaphaneity/amount of transparency - ability to allow light to pass through it. This is affected by chemical makeup of the mineral sample.  Properties of Minerals g. Luster - how light is reflected off a surface h. Tenacity - describes the minerals reaction to stress. i. Brittleness - a mineral turns into powder  Properties of Minerals j. Malleability - a mineral can be flattened by pounding with a hammer. k. Ductility - A mineral can be stretched into wire. l. Flexible but inelastic - Minerals are bent but they remain in the new position.  Properties of Minerals m. Flexible and elastic - Minerals are bent, and they bring back to their original position. n. Sectility - ability of minerals to be sliced by a knife.