Rocks

1. Rocks Building Blocks of the Earth’s Crust

2. Earth’s Layers

3. Chemical Composition of the Earth

4. Chemical Composition of the Earth’s Crust

5. Where the Rocks Are … The Crust

6. What Is a Rock? A rock is a mixture of minerals! What is a mineral? • naturally occurring (not man-made) • inorganic (not part of or a product of a (once) living organism ) • solid (not made of liquid or gas) • chemical compound • with a definite chemical structure which gives it unique physical properties. Minerals are the building blocks of rocks.

7. Minerals • minerals are compounds and compounds are composed of elements • What are the most common elements in the crust?Oxygen (O) and Silicon (Si) • the most common minerals aresilicates(contain silicon and oxygen) • the most common silicate – quartz

8. Physical Properties of Minerals • Hardness– what minerals can scratch it or be scratched by it • Cleavage– how does it break … along planes? • Streak– what does the powdered form look like • Color– what colors are common • Density– the mass of a given volume

9. Cleavage Halite Calcite

10. Rock Classification Rocks are divided into three major groupsbased on the methods of formation • Igneousrocks … from cooling lava or magma • Sedimentaryrocks … from compacted sediments • Metamorphicrocks … meta (change) morphic (form) … rocks changed by extreme forces

11. Rocks Classification • Rocks are further subdivided by • mineral composition • what minerals are present in large quantities • texture • what is the size of the mineral crystals (grains )

12. Igneous Rocks

13. Igneous Rocks Formed when molten rock cools and solidifies Lava Magma geollab.jmu.edu/Fichter/ IgnRx/Intrusiv.html

14. Volcano

15. Explosive vs Non-explosive

16. Magma intrusive – below the surface gathers in large bodies called plutons may become lava cools slowly – forms large crystals Lava extrusive - above the surface expelled from a fissure or a volcano begins as magma cools rapidly – forms small or no crystals Magma vs. Lava

17. Rich in silicates lots of feldspar, quartz, and other silicates lighter color more viscous – extrusives form steep volcanoes continental crust Poor in silicates lots of iron and magnesium rich minerals darker color less viscous – extrusives form large flows oceanic crust Mineral Composition of Igneous Rocks

18. Types of Common Igneous Rocks

19. Igneous Rocks Granite Rhyolite Gabbro Basalt

20. Other Important Volcanics • Pyroclastics – also calledejecta- thrown from the volcano – cool very quickly Obsidian – volcanic glass, a unique rock containing NO MINERALS Pumice – frothy volcanic glass

21. Sedimentary Rocks

22. Sedimentary Rocks • formed from sediments (particles) that settle in great amounts and are cemented together under great pressure • sedimentary rocks cover some 80% of the Earth's crust • generally, the only type of rock to contain fossils

23. Sedimentary Rock Formation • Clastic – particles deposited by water, wind, or ice • Chemical – particles precipitate from solution • Organic – growth in place (eg, coral reefs)

24. Clastic • basic sedimentary rock. • accumulations of pieces of broken up (eroded) rock (clasts) which have piled up and been "lithified“ (turned to rock) by compaction and cementation

25. Queen’s Throne, Utah

26. Clastic Sediments • formed from the erosion of other rocks • most sediments are carried by rivers and are deposited in great amounts in the ocean • under great pressure, these particles are cemented together • classified by particle size

27. Clastic Particles and the Corresponding Rocks Particle Rock Gravel Conglomerate Sand Sandstone Silt Siltstone Clay Claystone Shale

28. Chemical • some form when water conditions change causing solids to precipitate out of solution • some form when standing water evaporates, leaving dissolved minerals behind

29. Limestone

30. Chemical Sediments Deposit Rock Calcium Carbonate Limestone Calcium Magnesium DolomiteCarbonate Sodium Chloride (Salt) Halite

31. Organic • accumulation of sedimentary debris caused by organic processes • shells, bones, and teeth (calcium) • these bits of calcium can pile up on the seafloor and accumulate into a thick enough layer to form an "organic" sedimentary rock • Limestone can form this way; also, lignite, bituminous coal

32. Metamorphic Rocks

33. Metamorphic Rocks • metamorphics get their name from "meta" (change) and "morph" (form) • the rock is moved into an environment in which the minerals which make up the rock become unstable and out of equilibrium with the new environmental conditions • in most cases, this involves burial which leads to a rise in temperature and pressure

34. Metamorphic Rocks • the metamorphic changes in the minerals always move in a direction designed to restore equilibrium • any rock can become a metamorphic rock, including another metamorphic rock (can become a different metamorphic rock) • a metamorphic rock exposed to too much heat will melt and become ??? • common metamorphic rocks include slate, schist, gneiss, and marble

35. Metamorphic Rock - Gneiss www.nearctica.com/geology/ mineral/metamor.htm

36. Regional areas of great amounts of pressure (during mountain-building) usually associated also with high temperatures Contact near magma chambers (plutons) Types of Metamorphism

37. Types of Metamorphism Regional • areas of great amounts of pressure (during mountain-building), usually associated also with high temperatures • foliation of rocks present … pressure causes tabular minerals in the rock to grow parallel to each other and perpendicular to the direction of pressure (stress), generating a mineral alignment termed a foliation • rocks often look folded or wavy

38. Foliation Slate

39. Metamorphic Rock www.aqd.nps.gov/grd/usgsnps/ rxmin/rock3.html

40. Types of Metamorphism Contact • near magma chambers (plutons) • rocks in “contact” or near-contact with the magma are baked • new minerals are formed • rocks do not conduct heat well (they are good insulators) so the zone of contact metamorphism is usually relatively narrow • marble results from the contact metamorphism of limestone

41. Metamorphic Rock Marble

42. The Rock Cycle www.canadianrockhound.com/ junior/rock_cycle.html

43. http://www.ecomlink.org/MAP/Caribbean.gif

44. Likely geological origins of Caribbean islands • Many are extrusive volcanic islands • Eruption eventually above the surface of the water: Montserrat, Mt. Pelee, many others • Eruption below the surface and uplifted: St. John, St. Thomas • Some are flat limestone islands • Aruba, Anegada, Anguilla, Bonaire, Curacao • St. Croix is sedimentary, but has more complex origin • Barbados is an accretionary wedge.