4 Igneous Rocks Classification based on composition and texture. Principally the rock-forming mineralsOlivinePyroxenesAmphibolesMicasFeldsparsQuartzConstitute 95% of minerals inALL igneous rocks.
5 COMPOSITION You can determine basic igneous rock composition just by the COLOR of the rock.DARK COLORED igneous rocks = MAFICLIGHT COLORED igneous rocks = FELSICGRAY COLORED igneous rocks = INTERMEDIATEColor allows an approximation of igneous rockcompositionRelated to Bowen’s Reaction Series(red vs. green)
13 TEXTURE Types of Textures GlassyNo crystals, lava cools too fastExtremely fast cooling rate = VolcanicObsidian,PumiceLightFelsicPumiceObsidian
14 TEXTURE Types of Textures PorphyriticTwo distinct sizes of crystalsStarts cooling slowly, remainder cools quicklyPhenocrystsGroundmass
15 TEXTURE Types of Textures TEXTURE is related to origin of magma or lava.Phaneritic = Coarse-grained = IntrusivePlutonicAphanitic = Fine-grained = ExtrusiveGlassy or smaller VolcanicIdentification/Classification of Igneous RocksKey on page in lab manualChart on page 91 in lab manual
16 IGNEOUS ROCK CLASSIFICATION COMPOSITIONPHANERITICAPHANITICGLASSY
20 CLASTIC – fragments of rock debris Classified by analyzing grain-size TEXTURECLASTIC – fragments of rock debrisClassified by analyzing grain-sizeSediment Size(mm)Particle NameRock Name<0.00464-2564-642-4>256BoulderCobblePebbleGranuleSandSiltClayGravelMudConglomerateBrecciaSandstoneShaleSiltstoneMudstone
21 Particles>2mm = coarse-grained CONGLOMERATE(rounded clasts)BRECCIA(angular clasts)1/16 - 2mm = medium-grained SANDSTONE<2mm = fine-grained SHALESandstones further classified on the basis of theirmineralogical composition:Mostly quartz = QUARTZ SS.>25% feldspar = ARKOSE1/3 silt, clay and rock fragments = GREYWACKE
25 Chemical Sedimentary Rocks precipitated from sea water (evaporites)initially dissolved in watervery similar in appearance to igneous rocksexcept MONOMINERALIC.texture is crystalline if visiblemicrocrystalline if notOOLITIC LIMESTONECHERTDOLOMITE
33 NONCARBONATE ORGANIC SED. ROCKS CHERTmicrocrystallinecomposed of skeletons, microscopic in sizemade of SiO2hardness = 7may exhibit conchoidal fracture
34 NONCARBONATE ORGANIC SED. ROCKS PEATcomposed of compressed plant debrisbasic building block of coalused as a fuel source in some areas
35 Identification/Classification of Sedimentary Rocks Key on page in lab manualChart on page 93 in lab manual
36 Metamorphic Rocks Rocks are fundamentally changed by HEAT and/or PRESSUREMay be derived from ANY pre-existing rock typeCLASSIFICATIONbased on the presence or absence of FOLIATIONFOLIATION is the parallel alignment of the tabularminerals (micas and clay minerals) and byvarying degrees of banding.