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CEE 437 Lecture 11
Rock Classification
Thomas Doe
Translation of Mineral Properties to Rock Properties
Comparison of mineral properties to rock properties
Rocks have lower strength, especially tensile strengthAnisotropy of minerals and heterogeneity of minerals
ElasticityThermal expansionDiversity of mineral orientation
Creation of microcracks on mineral boundaries
Minerals – Summing Up
Most earth materials are minerals, that is, they are crystallineMineral structures can lead to anisotropic propertiesSilicates are the dominant rock-forming mineralsSheet silicates are important for engineering – micas and claysMineral heterogeneity and anisotropy leads to microcrackformation which greatly influences rock properties
Sedimentary Rocks
Clastics, Siliciclastics, and EvaporitesClastic rocks, depositional medium, and energyDiagenesis — chemical changes after deposition
Sedimentary Rocks and Rock Properties
Properties for a given geologic description vary wildly based on cementation, porosity and other diagenetic factors.Properties can be strongly anisotropic and heterogeneous based on bedding
Clastic Sedimentary Rocks
Clastic — broken like iconoclast)Often referred to as Siliciclastics as having Si based rock forming mineralsBased on grain size and to a lesser extent compositionGrain size related to energy of depositional environment
Relationship of medium velocity to maximum grain size)
Clastic Sedimentary Rocks
Clay, muds → shales, mudstones, claystones (difference based on fissility)Silts → siltstonesSands → sandstonesGravels → Conglomerates (Breccia if angular, breccia may also be a term for tectonically fragmented rock)
Weathering Cycle
Clastic Sediments
Lithification
Cementationdeposition of a material different from clasts
Crystallizationcrystal growth on clasts to fill pore space
CompactionDiagenesis
Early post-depositional chemical transformation of sediments, e.g. calcite to dolomite
Carbonates
Generally like siliciclastics — carbonate muds, sands, etc.Often deposited in reefsMajor portion of world oil depositsProperties depend strongly on post-depositional pore chemistry
CementationDissolution
Karst topography, cave formation
Carbonate Environments
Evaporites
Rock salt (NaCl), Gypsum-Anhydrite (CaSO4), Sylvite (KCl)Deposition in regions where evaporation exceeds recharge
desert lakesrestricted seas (Mediterranean)lagoons, back-reef areas
Subject to flow and diapirism
Other Sedimentary Rocks
Chert: finely crystalline silicaas replacement/diagenetic nodulesas bedded material from silica-shelled biota
CoalDerived from vegetation
Banded Iron FormationLikely bacteria derived, mainly Pre-Cambrian
Igneous Origins
IntrusiveBatholithic or plutonic: phaneriticDikes or sills that chill rapidly: aphanitic
Extrusivedeposition as melt (lava)pyroclastic
tufftephrapyroclastic flows
Geologic Settings for Igneous Rocks
OceanicHi Fe, Mg, Ca, low Sibasalt, gabbro
Continental Hi Si, Na, Kgranite, rhyolite, andesite
Differentiation of Crustal Composition
Weathering differentiating towards higher Silica
Preferential melting of high-silica materials
Concentration of C, Ca, Na, K in sea and air
Original basaltic composition of crust
Carbonate concentrated by organic processes
Identifying Igneous Rocks
ChemistryAcidic: Basic (more Si, less Si)
TextureAphanitic: crystals not visiblePhaneritic: made of visible crystal componentsPorphyritic: Larger crustals in aphanitic or phaneritic ground mass
Bowen’s Reaction Series
Igneous Rock Classification
SERPENTINITE
Acidic, Felsic Basic, Mafic Ultramafic
Extrusives
Viscosity varies with Si and water contentBasalt — low viscosityRhyolite — high viscosity
Rhyolite flows relatively unusual as rhyolite does not flow well
ExplosiveTuffs, pyroclastics
Volcano Types
Basaltic: low viscosity — Hawaii, Columbia Plateau
Andesitic/Rhyolitic
Structures of Basalt Flows
Lava TubesFlow Stratigraphy
collonadeentablatureflow top breccia/scoria
Hawaii Basalt Flows
Basalt Flow Structures
Eruptions of Acid-Rock Volcanoes
Rhyolite Dome
Mt. St. Helen’s Blast Zone
Mt. Mazama Ash Distribution
Basic Metamorphic Types
Quartz Sandstone → QuartziteLimestone, Dolomite → MarbleShale →
Slate — cleavage, no visible xl’sPhyllite — foliation, mica sheen but xl’s not visibleSchist — clear foliation, visible micaGneiss — like granite but with foliation/gneissosity
Basalt → greenschist, amphibolite
Non-foliated Metamorphic Rocks
Sandstone —> QuartziteLimestone —> MarbleDolomite —> Dolomitic Marble
Foliated Metamorphic Rocks
Shale/MudstoneSlatePhyllite (Greek for leaves e.g. phyllo dough)SchistGneiss
Origin of Foliation (gneissosity, schistosity)
Engineering Properties
Anisotropy of strength and elastic propertiesPreferred failure on foliation
Slate
Phyllite
Schist
Gneiss
Banded Gneiss
Metamorphic Grade
Subduction-Zone Metamorphism
Metamorphism at Continental Collisions
Contact Metamorphism
CEE 437 �Lecture 11� Rock ClassificationTranslation of Mineral Properties to Rock PropertiesMinerals – Summing UpSlide Number 4Slide Number 5Sedimentary RocksSedimentary Rocks and Rock PropertiesClastic Sedimentary RocksClastic Sedimentary RocksWeathering CycleClastic SedimentsLithificationCarbonatesCarbonate EnvironmentsEvaporitesOther Sedimentary RocksIgneous OriginsGeologic Settings for Igneous RocksDifferentiation of Crustal CompositionSlide Number 20Identifying Igneous RocksBowen’s Reaction SeriesIgneous Rock ClassificationExtrusivesVolcano TypesStructures of Basalt FlowsHawaii Basalt FlowsBasalt Flow StructuresEruptions of Acid-Rock VolcanoesRhyolite DomeMt. St. Helen’s Blast ZoneMt. Mazama Ash DistributionBasic Metamorphic TypesNon-foliated Metamorphic RocksFoliated Metamorphic RocksOrigin of Foliation (gneissosity, schistosity)Engineering PropertiesSlatePhylliteSchistGneissBanded GneissMetamorphic GradeSubduction-Zone MetamorphismMetamorphism at Continental CollisionsContact Metamorphism