Rocks Classification of Igneous Sedimentary and Metamorphic Rocks

Rocks Classification of Igneous, Sedimentary and Metamorphic Rocks

ROCK CYCLE • Equilibrium • Interrelationships between – – – igneous rocks sedimentary rocks metamorphic rocks weathering and erosion

IGNEOUS ROCKS EXTRUSIVE Volcanic- Fine-grained INTRUSIVE Plutonic- Coarse-grained

MAGMA • Molten Rock – Usually with dissolved gasses • Generated at depth • Eruptions if magma (lava) reaches surface • If doesn’t reach surface, Solidifies underground – – – Intrudes country or host rock Intrusive contact Xenolith- ‘foreign body’

Igneous Rocks • Names based on mineral composition reflects chemical composition of the magma and. . . Grain size – Very coarse-grained Pegmatitic – Coarse-grained: Phaneritic > 1 mm. – Fine-grained: Aphanitic < 1 mm. – Porphyritic- 2 crystal sizes

Igneous Rocks. Classification • Coarse-grained • Plutonic (Intrusive) – – Granite (Sialic) (SIlica and ALuminum rich) Diorite Gabbro (Mafic) (MAgnesium and iron (FE) rich) Dunite & Peridotite (Ultramafic) • Fine-Grained • Volcanic (Extrusive) – Rhyolite (Sialic) – Andesite – Basalt (Mafic)

Igneous Rock Identification • Granite (& Rhyolite) – – High in Si + O Low in Fe + Mg Mostly feldspar & Light-colored quartz • Basalt (& Gabbro) – – “Low” in Si + O High in Fe + Mg no quartz, abundant ferromagnesian minerals Dark colored • Andesite (& Diorite- intermediate)

WEATHERING, EROSION, TRANSPORTATION • Weathering- Physical disintegration and chemical decomposition of rocks • Erosion- Physical removal • Transportation- Movement of eroded particles • Chemical vs. Physical Weathering • Effects of weathering – – – Surface alteration of outcrops Spheroidal weathering Differential weathering

Physical Weathering

Differential Weathering

Frost Action

Exfoliation

Organic Action

ROCK CYCLE

Relative Percentages of Sedimentary Rocks

SEDIMENT • Particle size – Pebbles, cobbles, boulders – Gravel- > 2 mm – Sand- 2 mm - 0. 063 mm – Silt - 0. 063 mm - 0. 004 mm – Clay- < 0. 004 • Deposition Clay-sized particle vs. clay mineral

TYPES OF SEDIMENTARY ROCKS • Clastic or Detrital • Chemical- inorganic precipitation or evaporation • Biochemical- Organic remains – shells, charcoal, plant fragments

CLASTIC (Detrital) ROCKS • Breccia and Conglomerate (> 2 mm) – Sedimentary Breccia- angular fragments – Conglomerate- rounded fragments • Sandstone (2 mm - 0. 063 mm) – Quartz sandstone – Arkose (feldspar) – Graywacke (appreciable amounts of silt/clay) • Fine-grained Matrix • Usually from turbidity currents

Quartz Sandstone

• CHEMICAL SEDIMENTARY ROCKS Carbonate Rocks – Limestone- made of calcite • Inorganic varieties – micrite, oolites, travertine – Dolomite – Recrystallization • Chert- silica • Evaporites – Rock gypsum – Rock salt

BIOCHEMICAL SEDIMENTARY ROCKS • Coal – Develops from peat • plant fragments – Lignite – Bituminous Coal • Carbonate Rocks – Limestone- made of calcite • organic varieties – Coquina – Fossiliferous Limestone – Chalk

SEDIMENTARY STRUCTURES – Cross-bedding – Graded bed – Mud cracks – Ripple marks – Fossils

Mudcracks

Sedimentary Rocks as Resources • Non-Metallic – Sand gravel – Limestone – Clay – Gypsum • Energy Resources – Oil and Gas – Coal

Formation of Oil and Gas

U. S. Coal Production

Metamorphic Rocks • Metamorphism – Increase in Pressure; increase in Temperature • Burial • Contact • Regional • Metamorphic rock – Pre-existing rock – Parent rock

Foliation

Classification A- Slate C- Phyllite D- Schist E- Gneiss F- Migmatite

Classification