BASIC GEOLOGY Chapter 2 Common Rock Types Mining

BASIC GEOLOGY Chapter 2: Common Rock Types Mining Geology SMK N 1

Igneous Rocks Classification based on composition and texture. COMPOSITION Principally the rock-forming minerals Olivine Pyroxenes Amphiboles Micas Feldspars Quartz Constitute 95% of minerals in ALL igneous rocks.

COMPOSITION You can determine basic igneous rock composition just by the COLOR of the rock. DARK COLORED igneous rocks = MAFIC LIGHT COLORED igneous rocks = FELSIC GRAY COLORED igneous rocks = INTERMEDIATE Color allows an approximation of igneous rock composition Related to Bowen’s Reaction Series (red vs. green)

1200°C Gabbro-Basalt 900°C Diorite-Andesite Granite-Rhyolite 600°C

TEXTURE reflects cooling rate of magma or lava. SLOW COOLING = LARGE Crystals RAPID COOLING = SMALL Crystals SLOW COOLING = PLUTONIC RAPID COOLING = VOLCANIC

TEXTURE Types of Textures Phaneritic Large crystals > 2 mm Slow cooling rate = Plutonic Granite, Light Felsic Diorite, Gray Intermediate Gabbro Dark Mafic

TEXTURE Types of Textures Aphanitic Small crystals < 2 mm Fast cooling rate = Volcanic Rhyolite, Felsite Light Felsic Andesite, Gray Intermediate Massive Basalt Scoria Dark Mafic

Rhyolite Felsite

Andesite

Massive Basalt Scoria

TEXTURE Types of Textures Glassy No crystals, lava cools too fast Extremely fast cooling rate = Obsidian, Pumice Light Felsic Volcanic Pumice Obsidian

TEXTURE Types of Textures Porphyritic Two distinct sizes of crystals Starts cooling slowly, remainder cools quickly Phenocrysts Groundmass

TEXTURE Types of Textures TEXTURE is related to origin of magma or lava. Phaneritic = Coarse-grained = Intrusive Plutonic Aphanitic = Glassy Fine-grained or smaller = Extrusive Volcanic Identification/Classification of Igneous Rocks Key on page 75 -77 in lab manual Chart on page 91 in lab manual

IGNEOUS ROCK CLASSIFICATION COMPOSITION PHANERITIC APHANITIC GLASSY

Sedimentary Rocks Clastic Sedimentary Rocks COMPOSITION Derived from pre-existing rocks. Five main constituents: Quartz Feldspar Rock fragments Clay (and clay minerals) Calcite

TEXTURE CLASTIC – fragments of rock debris Classified by analyzing grain-size Sediment Size (mm) Particle Name >256 Boulder 64 -256 Cobble 4 -64 Pebble 2 -4 Granule 0. 063 -2 Sandstone 0. 004 -0. 063 Siltstone <0. 004 Clay Rock Name Gravel Mud Conglomerate Breccia Shale Mudstone

Particles >2 mm = coarse-grained CONGLOMERATE (rounded clasts) BRECCIA (angular clasts) 1/16 - 2 mm = medium-grained SANDSTONE <2 mm = fine-grained SHALE Sandstones further classified on the basis of their mineralogical composition: Mostly quartz >25% feldspar 1/3 silt, clay and rock fragments = QUARTZ SS. = ARKOSE = GREYWACKE

Coarse-grained Clastic Sedimentary Rocks Conglomerate Breccia

Medium-grained Clastic Sedimentary Rocks Sandstones Arkose Greywacke Qtz. Sandstone

Fine-grained Clastic Sedimentary Rocks Shale

Sedimentary Rocks Chemical Sedimentary Rocks CHEMICAL SEDIMENTARY ROCKS precipitated from sea water (evaporites) initially dissolved in water very similar in appearance to igneous rocks except MONOMINERALIC. texture is crystalline if visible microcrystalline if not OOLITIC LIMESTONE CHERT DOLOMITE

Oolitic Limestone

Chert

Dolostone

CHEMICAL SEDIMENTARY ROCKS ROCK SALT or HALITE composed of halite (Na. Cl) microcrystalline to crystalline precipitates from sea water forms economic deposits

Sedimentary Rocks Organic Sedimentary Rocks ORGANIC or BIOCLASTIC SEDIMENTARY ROCKS can be crystalline or clastic (bioclastic) all particles are derived from organisms typically composed of calcite or aragonite (Ca. CO 3)

Lithographic Limestone or Micrite Very fine-grained limestone Formed from calcareous algae Fizzes in HCl

Fossiliferous Limestone

NONCARBONATE ORGANIC SED. ROCKS CHERT microcrystalline composed of skeletons, microscopic in size made of Si. O 2 hardness = 7 may exhibit conchoidal fracture

NONCARBONATE ORGANIC SED. ROCKS PEAT composed of compressed plant debris basic building block of coal used as a fuel source in some areas

Identification/Classification of Sedimentary Rocks Key on page 79 -80 in lab manual Chart on page 93 in lab manual

Metamorphic Rocks are fundamentally changed by HEAT and/or PRESSURE May be derived from ANY pre-existing rock type CLASSIFICATION based on the presence or absence of FOLIATION is the parallel alignment of the tabular minerals (micas and clay minerals) and by varying degrees of banding.

Metamorphic Rocks Types of Foliation Slatey cleavage very fine-grained rocks Usually found in slate and phyllite

Metamorphic Rocks Types of Foliation Schistosity platy minerals visible Usually found in schist

Metamorphic Rocks Types of Foliation Gneissic banding minerals segregated into bands Usually found in gneiss

Metamorphic Rocks Foliated Rocks SLATE PHYLLITE Have slatey cleavage Rock splits along parallel planes SCHIST Has schistosity GNEISS Has gneissic banding

Metamorphic Rocks Nonfoliated Rocks NO structure is apparent in the rock Rock is typically MASSIVE (monomineralic)

Metamorphic Rocks Nonfoliated Rocks MARBLE Is composed of calcite (Ca. CO 3), soft H = 3 Will react to dilute hydrochloric acid

Metamorphic Rocks Nonfoliated Rocks QUARTZITE Metamorphosed quartz sandstone Hardness = 7

Metamorphic Rocks Nonfoliated Rocks ANTHRACITE COAL Formed from organic material (plant debris) Contains no minerals

Metamorphic Rocks Nonfoliated Rocks GREENSTONE Composed of metamorphosed mafic igneous rocks

Identification/Classification of Metamorphic Rocks Key on page 82 in lab manual Chart on page 95 in lab manual