ROCKS

• rocks - a naturally-occurring aggregate of two or more minerals
• rocks - may or may not contain mineraloids, natural glass, organic matter, and pre-existing rocks or sediment
• petrology - study of rocks; its genesis, composition, distribution and structure of rocks.
• petrology - examining the processes that lead to the formation of rocks, as well as their identification and classification
• petrography - branch of petrology that deals with the description and classification of rocks; their constituent minerals and texture
• petrography - involves the use of microscopic and laboratory techniques to study the rock in details
• rock cycle - explains the processes underwent by rocks on and under the earth’s surface
• rock cycle - allows us to view many of the interrelationships among different parts of the earth’s system
• igneous rocks - formed from cooling of magma
• sedimentary rocks - formed when weathered fragments of other rocks are compressed and cemented together, precipitation from solution
• metamorphic rocks - formed by alteration (due to heat, pressure, and/ or chemical action) of pre-existing rock (igneous, sedimentary, or metamorphic rock)
• the temperature of magma ranges from 600° – 1200°C
• magma - molten or partially molten rock composed of varying amounts of:

  LIQUID: silicates (sometimes carbonate, sulfides, or oxides) and ions of Al, Fe, Ca, Na, K, Mg

  SOLIDS: mineral or rock fragments

  DISSOLVED GAS OR VOLATILES: H2O, CO2, SO2
• classification of magma based on its silica content: felsic, intermediate, mafic, ultramafic
• felsic - silicic or acidic, >63% SiO2, mostly continental crust
• intermediate - 52-63% SiO2, continental crust
• mafic - basic, 45-52% SiO2
• ultramafic - ultrabasic, <45% SiO2
• another classification of magma - viscosity, density, temperature
• viscosity - property to resist flow

  higher temp, lower viscosity

  higher SiO2, higher viscosity

  higher dissolved H2O, lower viscosity
• density

  denser oceanic crust – mafic rocks

  lighter continental crust – felsic rocks
• temperature - temperature of the melt formation
• common types of magma - basaltic and granitic/rhyolitic
• basaltic magma - high silica content, low iron content, low magnesium content
• granitic/rhyolitic magma - magma that is rich in silica and magnesium
• sources of heat:

  original heat of the earth at the time of formation

  some elements (e.g., uranium) produces heat through radioactive decay

  heat transfer from nearby magmatic body

  hot mantle plumes may upwell into the crust

  frictional heat formed by two crust grinding past each other
• magma generates through melting in the upper mantle/lower crust
• heat - increase in temperature; reaching the melting point
• pressure - lowering the pressure ; decompression melting
• volatiles - addition of volatiles; lowers the melting temperature
• new magma is generated in:

  mid-oceanic ridges

  subduction zones

  hot spots
• magmatic differentiation - any process that causes the magmatic composition to change
• magmatic differentiation can be any of the ff:

  FRACTIONAL DIFFERENTIATION

  PARTIAL MELTING

  COUNTRY ROCK ASSIMILATION

  MAGMA MIXING
• igneous rocks - formed from solidification of molten material called magma (intrusive) or lava which flows out from the depths (extrusive)
• "ignis" means fire
• bowen's reaction series - As magma cools, certain minerals crystallize first at relatively high temperature, in successively lower temperature, other minerals begins to crystallize
• discontinuous series - describes the crystallization of specific minerals as temperature decreases
• continuous series - sequence of mineral that form as temperature in a more gradual manner; doesn’t involve discrete phases like the discontinuous series
• 2 kinds of igneous rocks - intrusive or plutonic and extrusive or volcanic
• intrusives (plutonic) - igneous rocks formed at the depth

  e.g. peridotite, gabbro, diorite, granite