Lecture 10 (09182024) PDF

Interlude A Introducing Rocks Copyright © 2022 W. W. Norton & Company, Inc. What is a rock?  Rock: A coherent, naturally occurring solid that consists of an aggregate of minerals or, less common, a body of glass.  Eg: Clastic rocks (Sedimentary in origin) are held together by cement. I...

Interlude A Introducing Rocks Copyright © 2022 W. W. Norton & Company, Inc. What is a rock?  Rock: A coherent, naturally occurring solid that consists of an aggregate of minerals or, less common, a body of glass.  Eg: Clastic rocks (Sedimentary in origin) are held together by cement. Interlocking Crystals Hold Rocks Together  Crystalline rocks (mostly igneous in origin) are held together by interlocking crystals. Class Question 1 Granite is considered what type of rock? A. cement B. clastic C. crystalline D. coherent Class Question 1 Answer Granite is considered what type of rock? A. cement B. clastic C. crystalline (Correct) D. coherent Bedrock Is Attached to Earth’s Crust  An exposure of bedrock is called an outcrop.  Broken pieces of rock on Earth’s surface are not bedrock.  Exposures of bedrock can be either natural or human-made. Rocks Are Classified By Their Origin – 1  Igneous rock forms from molten material. Rocks Are Classified By Their Origin – 2  Sedimentary rocks form by cementation or precipitation.  Sand on the beach in the picture formed from grains eroded from the cliff rocks.  If the sand is buried and turned into rock, it becomes layers of sandstone, like those that make up the cliffs in the photo. Rocks Are Classified By Their Origin – 3  Metamorphic rocks form when pre- existing rocks change character due to a change in temperature and/or pressure conditions. Rock-Forming Environments  There are three different rock types: Sedimentary, metamorphic, and igneous and they can form in different environments. Rock Groups: Animation Class Question 2 A rock can be assigned to one of ________ rock groups, based on how the rock formed. A. one B. two C. three D. four E. five Class Question 2 Answer A rock can be assigned to one of ________ rock groups, based on how the rock formed. A. one B. two C. three (Correct) D. four E. five Physical Characteristics of Rocks  Grain size is variable.  Grain shape is variable. Composition and Texture  Composition refers to the proportions of chemicals that make up a rock and affects minerals present in rocks.  Texture refers to the configuration of grains in a rock and how those grains connect. Layering and Foliation  Layering is defined by bands of different compositions, grain sizes, textures, or alignment of grains.  Foliation is defined by the difference in mineral composition. Studying Rocks  Rocks are studied at various scales.  Outcrops reveal relationships between rock and surrounding rocks.  Rock hammers are used to obtain hand samples (fist-sized pieces of rock) for study. Hand Sample & Hand Lens  A hand sample can reveal the  Geologists use polarized light to mineralogy and texture of a rock. view a thin section.. Petrographic Microscope  Thin sections are very thin (~0.03 mm) slices of rock mounted on small glass plates.  Thin sections are studied with polarized light through a petrographic microscope that reveals characteristics of individual mineral grains.  Photomicrographs are photographs of these thin sections. Electron Microprobe  For high-tech, more detailed studies of rocks, a scanning electron microscope (SEM) or an electron microprobe can be used. X-ray Diffractometers  For high-tech, more detailed studies of rocks, a mass spectrometer or an X-Ray diffractometer can be used. Think-Pair-Share  Is concrete a rock? Why or why not? What about “granite” countertops?