Earth Materials--Rocks and Minerals CHAPTER 2
Minerals and Rocks Definition of a mineral: • Naturally occurring • Inorganic • Solid • Definite chemical composition (or range) • Orderly internal crystal structure
Mineral Importance • Economic • Conditions of environment • Definition of a Rock: • An aggregate or one or more minerals
Physical Properties of Minerals • Color - the color of the mineral as it appears to the naked eye in reflected light. • Luster - the character of the light reflected from the mineral. A mineral may have a metallic luster or a non-metallic luster. • Hardness - the resistance of a mineral to scratching. Hardness is measured on a scale of 1 - 10 called Mohs Hardness Scale. Hardness of minerals can also be compared to common objects (fingernail, copper penny, nail, glass).
Physical Properties of Minerals • Cleavage - the tendency of a mineral to break along flat surfaces related to planes of weakness in its crystal structure. • Fracture - irregular breakage not related to planes of weakness in the mineral. • Magnetism. • Reaction to acid - The carbonate minerals react with diluted hydrochloric acid (HCl) by effervescing or fizzing, producing bubbles of carbon dioxide gas.
Silicate Minerals Silicate Minerals: have Si and O in their formulas • Feldspars (60% of Earth's crust): plagioclase and orthoclase varieties • Quartz • Micas: muscovite and biotite • Hornblende (amphibole) • Pyroxene (augite) • Olivine • Clay minerals
Minerals Nonsilicate minerals (8% of Earth's crust) • Carbonates (with CO2): dolomite, calcite, aragonite • Oxides (with O): hematite, goethite, limonite • Halides (with Cl): halite, sylvite • Sulfates (with SO4): gypsum, anhydrite • Sulfides (with S): pyrite, galena • Native elements: gold, copper, silver
Figure 2-12 Geologic processes act continuously on Earth to change one type of rock into another.
Igneous Rocks Igneous Rocks (90% by volume of Earth's crust) • Cooling history of magma or lava is reflected in the texture • intrusive (plutons, dikes, sills) = phaneritic (coarse) texture • extrusive (lava flows, ash falls) = aphanitic (fine) texture • two-stage (slow cooling followed by more rapid cooling) = porphyritic texture • Very rapid cooling may result in glassy texture
Mineral composition, texture, and other properties of common igneous rocks.
Igneous Rocks Crystallization of magma • first-formed minerals have more perfect shapes • Bowen’s reaction series helps us understand order of mineral formation: • continuous reaction series: feldspar composition changes • discontinuous reaction series: iron-rich silicate minerals reacts with liquid
A depiction of Bowen’s Reaction Series.Note that the earliest minerals to crystallize are olivine and calcium-rich plagioglase. As crystallization proceeds, each mineral reacts with the melt to form the mineral beneath it.
Volcanic Activity Volcanism (volcanic activity) • Explosive- High Water, High Silica, High Viscosity (example: andesitic) • Quiet-Low viscosity, Low Silica, Low water content (example: basalt)
An andesitic melt resulting from fractional crystallization of a basaltic magma.
Sedimentary Rocks • Sediment = loose particulate material (clay, sand, gravel, etc.) • Derivation by weathering • decomposition (chemical) • disintegration (physical) • Sediment becomes sedimentary rock through lithification, which involves: • Compaction • Cementation • Recrystallization (of carbonate sediment)
A conceptual diagram showing how the weathering of granitic rock yields quartz grains for quartz sandstone, clay for shale, and calcium for limestone.
Types of Sedimentary Rocks • Clastic (also called terrigenous or detrital) • Conglomerate or Breccia • Sandstone • Siltstone • Shale or Claystone
Clastic Sedimentary Rocks Shale Sandstone Conglomerate Breccia
Chemical/Biogenic Sedimentary Rocks • Chemical/biochemical • Evaporites • Carbonate sedimentary rocks (limestones and dolostone) • Siliceous sedimentary rocks • Organic (coals)
Carbonate (calcite) Halite Coal Chert
Metamorphic Rocks Metamorphic means "changed form" • Agents of metamorphism • Heat • Pressure • Chemically active fluids
Types of Metamorphism • Contact metamorphism -alteration of rock by heat adjacent to lava or magma • Regional metamorphism - alteration of rock over a large area by heat and pressure due to deep burial or tectonic pressure
Changes in minerals that will develop during the progressive metamorphism of shale
Texture of Metamorphic Rocks • Foliation - laminated structure in a metamorphic rock resulting from the alignment of sheet-like minerals (usually micas). • Non-foliated or granular metamorphic rocks are those which are composed of equidimensional grains such as quartz or calcite. There is no preferred orientation. The grains form a mosaic.
Foliated Metamorphic Rocks The following are derived from the progressive metamorphism of shale: • Slate • Phyllite • Schist • Gneiss (can also form from the metamorphism of granite)
Foliated Metamorphic Rocks Slate Phyllite Schist Gneiss
Non-foliated Metamorphic Rocks • Marble – parent rock is limestone or dolomite • Quartzite – parent rock is sandstone • Hornfels – parent rock is shale or siltstone • Greenstone – parent rock is basalt
Non-foliated rocks Marble Quartzite