[M4] Rocks

• 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.
• rock forms: igneous, sedimentary, and metamorphic rock.
• Petrology is the scientific study of rocks.
• Igneous - formed from hardening and crystallization of magma or molten material that originates deep within the earth
• Two types of igneous rock: Extrusive/Volcanic rock, and Intrusive/Plutonic
• 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.
• Intrusive/Plutonic - It cools slowly beneath the Earth surface and are created by magma. The intrusive igneous rocks have very large crystals (coarse grained).
• Composition- it refers to rock’s mineral and chemical make-up.
• Felsic – igneous rocks that are light in colors; feldspar and silicates
• Mafic – dark-colored igneous rocks made up of magnesium, calcium and iron
• Intermediate – refers to igneous rocks between mafic and felsic composition.
• Ultramafic – denotes igneous rocks that composed chiefly of mafic minerals.
• Texture - overall appearance of a rock based on the size, shape, and arrangement of interlocking mineral crystals.
• Aphanistic – fine-grained rocks with crystals seen by aid of microscope.
• Phaneritic - coarse-grained rocks
• Porphyritic – large crystals with small crystals
• Glassy - a rock that looks like colored glass with no visible mineral crystal.
• Pyroclastic- results from explosive fragmentation of volcanic material.
• Igneous Examples: Obsidian, pumice, basalt, granite, diorite, gabbro
• Metamorphic - forms from pre-existing rocks: either metamorphic, igneous, sedimentary or other metamorphic rocks that have been altered by agents of metamorphism
• Metamorphic Examples: quartzite, marble, slate, phyllite
• Metamorphism - transformation of one rock type into another.
• 2 types of metamorphism: Regional and Contact
• Regional - due to changes in pressure and temperature over large region of the crust.
• Regional may happen when rock is buried deep below the surface of the earth
• Contact - the rock minerals and textures are changed mainly by heat due to contact with magma
• Texture - refers to the size arrangement and grains within the rock
• Foliation - any planar arrangement of mineral grains or structural features within the rock.
• Foliated rocks – can be arranged in terms of increasing metamorphism, and it appeared layered or banded with compressed mineral grains. Example: mica
• Non-foliated rocks – usually made up of only few minerals
• 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.
• Three types of sedimentary rocks: Clastic Sedimentary rock, Chemical, Organic
• Clastic Sedimentary rock - formed from accumulation of clasts: little pieces of broken rocks and shells.
• Chemical - formed when dissolved minerals precipitate from a solution.
• Organic - rocks formed from the accumulation of animal debris