Chapter 4 Petrology/geology=study of rocks

Rocks are the record of our planet’s past…interesting where rivers used to flow where huge inland seas were located what lived in these waters stories of glaciers and how an ice age changed the planet ancient climates

“How are rocks alike & different?” Look at marble and conglomerate Describe the two (include color and texture) marble conglomerate

What is a ROCK? --start your study guide A MIXTURE of minerals (and sometimes organic matter, like shells) Example: look at granite quartz (35%) mica (10%) feldspar & (hornblend) (55%) Note: ratio can vary a bit Rocks are NOT elements or compounds.

What minerals make up other rocks? (don’t memorize) Basalt —pyroxene, olivine, augite, feldspar Marble —dolomite or calcite Rock salt —halite Sandstone —quartz and feldspar Limestone —mostly calcite Diorite —feldspar, hornblende, mica, quartz Gabbro —feldspar, augite, olivine Rhyolite —quartz, feldspar, hornblende, mica Andesite —feldspar, hornblende, mica

How geologists classify and identify rocks: 1. Texture 2. Composition 3. Origin

This has been your Public Service Announcement on Rocks… PERFORMANCE TASK 1 CAN BE COMPLETED NOW!!!

1. Texture (look at the grains)—are the grains large/small, smooth/pointy, glassy, smooth, chalky, etc? b. Grain shape smooth and rounded (like conglomerate) jagged (breccia) c. Grain pattern wavy, swirling pattern flat layers rows of multicolored bands (ex: gneiss) random pattern a. Grain size (1) coarse-grained= can be seen without microscope (2) fine-grained= only seen with microscope (3) no crystals/grains because it formed too quickly (smooth & shiny like obsidian)

2. Mineral composition (what the rock is made of) Ex: Limestone 95% calcite 5% aragonite scientists look at a very thin slice under microscope and do tests acid test look for rocks that have calcite magnet test look for iron or nickel

Origin of the rock (how & where did the rock FORM?) 1. Igneous (intrusive & extrusive—we’ll talk more about the 2 types later) forms when molten material (magma/lava) cools and hardens can form at surface or underground Ex: granite, basalt, pumice, obsidian

2. Sedimentary (clastic, chemical & organic-we’ll talk about the 3 types in more detail later) Usually form under water & have layers Particles called sediment (ex: pieces of rock, mud, sand, shells and dust) cemented and/or pressed together by pressure above takes millions of years most rocks (3/4) on earth are sedimentary Ex of sedimentary rocks: sandstone, shale, limestone Some sedimentary rock have fossils from extinct animals/plants (paleontology).

3. Metamorphic (foliated & nonfoliated —we’ll discuss the 2 types later) due to extreme heat, pressure, and/or chemical reactions DEEP underground over 10 km deep 100-800°C Ex of metamorphic rock: slate, schist, and marble

Questions Which type of rock forms the fastest? What is a ROCK? >>volcanic (extrusive) igneous What is a ROCK? >>mixture of minerals (sometimes contains organic material) What forces on Earth cause rocks to form? >>heat, pressure What can rocks tell us about the Earth’s past? >>age, what lived, climate, forces List the 3 BASIC types of rocks. >>igneous, metamorphic, sedimentary What is the study of rocks called? >>petrology (type of geology)

Questions: Which kinds of rock forms from material that settles on the ocean floor? >>sedimentary Molten rock beneath Earth’s surface is called _______. >>magma Which type of rock is MOST LIKELY to form layers? How do scientists classify rocks? >>according to the way they were formed (origin), as well as their texture and mineral composition