Earth Materials--Rocks and Minerals

1. Earth Materials--Rocks and Minerals CHAPTER 2

2. Minerals and Rocks Definition of a mineral: • Naturally occurring • Inorganic • Solid • Definite chemical composition (or range) • Orderly internal crystal structure

3. Mineral Importance • Economic • Conditions of environment • Definition of a Rock: • An aggregate or one or more minerals

4. 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).

5. 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.

7. 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

8. 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

9. Figure 2-12 Geologic processes act continuously on Earth to change one type of rock into another.

10. 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

11. Igneous textures

12. Mineral composition, texture, and other properties of common igneous rocks.

13. 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

14. 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.

15. Volcanic Activity Volcanism (volcanic activity) • Explosive- High Water, High Silica, High Viscosity (example: andesitic) • Quiet-Low viscosity, Low Silica, Low water content (example: basalt)

16. An andesitic melt resulting from fractional crystallization of a basaltic magma.

17. 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)

18. A conceptual diagram showing how the weathering of granitic rock yields quartz grains for quartz sandstone, clay for shale, and calcium for limestone.

19. Types of Sedimentary Rocks • Clastic (also called terrigenous or detrital) • Conglomerate or Breccia • Sandstone • Siltstone • Shale or Claystone

20. Clastic Sedimentary Rocks Shale Sandstone Conglomerate Breccia

21. Chemical/Biogenic Sedimentary Rocks • Chemical/biochemical • Evaporites • Carbonate sedimentary rocks (limestones and dolostone) • Siliceous sedimentary rocks • Organic (coals)

22. Carbonate (calcite) Halite Coal Chert

23. Metamorphic Rocks Metamorphic means "changed form" • Agents of metamorphism • Heat • Pressure • Chemically active fluids

24. 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

25. Changes in minerals that will develop during the progressive metamorphism of shale

26. 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.

27. 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)

28. Foliated Metamorphic Rocks Slate Phyllite Schist Gneiss

29. 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

30. Non-foliated rocks Marble Quartzite