Similarities of Rocks and Minerals
•Inorganic compounds (non-living) •Both can be classified by their chemical composition. •Solids •Naturally formed •Found around the world in many of the same places on Earth Rocks •Most commonly classified by how they form. 1.Sedimentary 2.Metamorphic 3.Igneous •Composed of more than one mineral. •No definite chemical composition. •No definite crystal structure. Minerals In addition to being inorganic, solid, and naturally formed like rocks, minerals also have: •A definite chemical composition. (amounts of elements present) •A definite crystal structure. (unique arrangement of atoms/molecules) Mineral Identification – Important Vocabulary 1.Color (green, red, yellow, blue, etc.) 2.Streak (Color of the streak across a streak plate) 3.Luster (Metallic or Non-Metallic) 4.Hardness (Mohs Scale) 5.Density (Specific gravity) 6.Breakage Pattern (Cleavage and Fracture) Color •Many minerals have distinctive colors, but they come in a variety of hues. •Color should never be used as the only test for identifying a mineral. Streak •The color a mineral displays in a finely powdered form •Might be completely different from the color of the mineral itself •To determine the streak, rub the mineral across a piece of unglazed porcelain know as a streak plate. Luster •The way a mineral’s surface reflects light. •Two types of luster •Metallic – shiny like a metal •Nonmetallic – several kinds 1. Glassy - quartz 2. Pearly - talc 3. Greasy - graphite 4. Silky – gypsum 5. Resinous - sulfur 6. Adamantine - diamond Hardness •One of the most reliable ways to identify minerals •Compares the resistance of a mineral to being scratched by 10 reference minerals •Called the Mohs Hardness Scale •Named after Friedrich Mohs, a German mineralogist, who developed the scale in 1812 Density •Defined as the amount of matter per unit volume •Density = mass divided by volume •In minerals, the term specific gravity is used in describing density. •In this way minerals can be compared and identified. Cleavage •Refers to the way some minerals break along certain lines of weakness in their structure Mica is a good example. Fracture •A description of the way a mineral tends to break •Some different types of fracturing 1. Conchoidal – smooth curve 2. Hackly – sharp jagged edges 3. Uneven – rough and irregular 4. Fibrous – shows fibers Gemstones •Some minerals are cut to become precious gemstones. •This is another use for minerals. •What’s your birthday gemstone? Earth Scientists
•Geologist – a scientist who studies the Earth’s crust as well as the processes and history that shaped it •Paleontologist – a scientist that studies fossil remains found on the Earth’s surface in order to study primitive life forms such as: plants, animals, fungi, and bacteria Stratigraphy •A branch of geology dealing with the arrangement of sedimentary rock layers or strata •Geologists assume the newest rock layers are on top of the older ones, unless some type of disturbance occurs. •Called the Law of Superposition Relative Age •The strata of sedimentary rocks is important in determining their relative age. •Relative age determines the “relative” order of past events but not the absolute age. •Like saying you’re relatively younger than your grandfather. Relative Age •Strata is sometimes disturbed. •Here we see a fault (E) and an igneous intrusion (D) •See if you can determine the order of the strata in this diagram. •Determining relative age in the field is sometimes very difficult because of these disturbances. Fossils •Preserved remains or traces of animals, plants, and other organisms from the remote past •Fossil Record – History of life as documented by all fossils, preserved in sedimentary rock strata •Provides a snapshot of past events in Earth’s geological history Index Fossils •Special fossils called “index fossils” indicate to geologists the boundaries in geological time. •This is another tool to determine the age of rocks. •Characteristics of Index Fossils •Easily recognizable •Abundant •Wide geographic distribution •Live a short time Fossil Record and Rock Strata •Index fossils are used to correlate the age of the rock strata •If two different rock strata in different areas on Earth contain the same index fossils, then the strata are probably the same age. Absolute Age •Most accurate form of dating, also call radiometric dating. •Uses the decay of radioactive elements to find the absolute age of a rock or fossil •This relies on the property of half life, which is the predictable time an element takes to decay. •Geologists tend to mix and match relative age and absolute age dates to piece together a geologic history. • Like saying you are 12 years old and your grandfather is 72 (absolute) instead of you are younger than your grandfather (relative). Geologic Time Scale •All of Earth’s geological history represented on a chronological time chart •Based on rock strata and the fossil record •Broken into different time chunks, the largest being the Eon, then Era, Period, and Epoch. •m.y. stands for millions of years. This diagram is not to scale. •Look how much of the Earth’s geologic history falls into Hadean, Archean, and Proterozoic (together called Precambrian) - 88% •If this were a clock, humans show up 11:58:43pm. •Notice some of the important events which happened over 4.6 b.y. Precambrian •Broken into 3 parts Hadean, Archean, and Proterozoic •Marks the beginning of Earth approximately 4.6 b.y. •Oldest rock fragment on Earth contains a mineral, zircon, that is 4.4 m.y.(found in Australia) •Very primitive life forms: one-celled animals, bacteria, jellyfish Paleozoic Era (early life) •Marks the formation of the super continent, Pangaea •Life developed rapidly •Marine plants and invertebrates •Fish and ferns •Amphibians •Mass extinction at the end of Paleozoic Mesozoic Era (middle life) •Increased complex life forms including: •Dinosaurs •Small mammals •Birds •Conifers and flowering plants •Rocks in the Petrified Forest in AZ were deposited during this time. •Another mass extinction at end of Mesozoic. Cenozoic Era (late life) •Currently in this Era •Development of: •Large mammals •Human beings •Periods of ice ages played a role in the formation of the geological features visible on Earth today. •Precambrian Time (0-87 yards) •Paleozoic Era(87-95 yards) •Mesozoic Era (95-98.5 yards) •Cenozoic Era (98.5-100 yards) Living Organisms •Fossils of previous living organisms are used to further divide Earth’s geologic history. •Life on Earth has changed over time or evolved quite a lot in 4.6 b.y. •We live in the Cenozoic Era which is further broken down into Epochs. •In which Epoch do we live? Geologic Time Scale •During the Earth’s 4.6 billion years, it has suffered 5 major mass extinctions. •An extinction is the end of a group of organisms, usually a species. Dinosaur Extinction •Most recent extinction is called the Cretaceous-Tertiary extinction event. •Happened 65.5 m.y. ago •Climate and geologic changes are thought to have weakened the dinosaurs. •A meteor strike was probably the final blow. What are fossils?
•Preserved remains or traces of animals, plants, and other organism from the remote past •Found in sedimentary rock layers •Can be as small as bacteria or as giant as a dinosaur •Paleontology is the study of fossils. Condition for forming fossils? •Quick burial of organism •Layers of sediments build up over the organism •Left for a long period of time •Most fossil remains are from hard structures such as bones and teeth. Erosion and uplifting exposes them to the Earth’s surface Sedimentary Rocks •Formed in layers by the deposition of weathered rocks •Sediments are pressed and cemented together. •Fossils are found here because sedimentary rocks form at low temperatures and pressure. •Fossils and the rock layer in which they are found are approximately the same age. Law of Superposition •Geologists assume the newest rock layers are on top of the older ones, unless some type of disturbance occurs. •This law helps scientists determine the age of fossils, relatively speaking. •They can say one fossil is older than another because of the strata in which it was found. Fossil Record •History of life as documented by fossils •Tells us when organisms lived and how they changed over millions of years (evolved) •Can also give us a clue as to the environment at that time •Recorded on the Geologic Time Scale Types of Fossilization •Petrification •Replacement •Permineralization •Molds and Casts •Carbonization •Fossil Resin (amber) •Tar and Ice •Trace Fossils Petrification •Two types – Replacement and Permineralization •Both result in organic material converting into stone or a similar substance •Petrified wood is the most well know example of this process. Replacement •Happens when water dissolves the original solid material and replaces them with mineral matter such as calcite, silica, pyrite and hematite •Happens slowly •Bones, shells, and wood are often fossilized in this manner. Permineralization •Groundwater carries dissolved minerals into the pores and cavities of bone, wood, or shells. •The original material is preserved rather than replaced. •Bones, teeth, and shells can be preserved this way. Molds and Casts •Mold – organism dies and there is no filling of the cavity with minerals •Cast – organism dies and the cavity fills with minerals, maybe sand or clay •Many times shells are fossilized through these processes. Carbonization •The process by which all substances of plants and animals decay, except carbon. •This leaves a carbon film on the sedimentary rock. •This process particularly occurs in plants and fish. Fossil Resin •Resin is excreted from certain plants, which is thought to protect them from insects and seals off plant injuries. •The sticky resin captures insects and other invertebrates. •It hardens and they are preserved in the resin including their DNA. •Fossil resin is known as amber. Tar and Ice •An animal can become trapped in tar and the whole body can be preserved. An example is the La Brea Tar Pits L.A. •Freezing can also trap whole animals. Mammoth’s bodies have been found with skin, hair and even organs. Trace Fossils •Provides indirect evidence of life in the past rather than the body of the animal itself. •Examples of trace fossils •Footprints •Tracks •Burrows •Feces •Borings Index Fossils •Special fossils called “index fossils” indicate to geologists the boundaries in geological time. •This is a tool to determine the age of rocks. •Characteristics of Index Fossils •Easily recognizable •Abundant •Wide geographic distribution •Lived a short period of geological time Fossil Record and Rock Strata •Index fossils are used to correlate the age of the rock strata. •If two different rock strata in different areas on Earth contain the same index fossils, then the strata are probably the same age. •Also called ‘relative age’ Absolute Age •Most accurate form of dating, also call radiometric dating •Uses the decay of radioactive elements to find the absolute age of a rock or fossil •This relies on the property of half life, which is the predictable time an element takes to decay. Stomatolites •Rock like structures built by blue-green algae. •First forms of life on Earth - oldest known fossils (3.5 b.y.) •Still found in some remote areas of the world today Fossil Record •By using relative and absolute dating scientists are able to put together the Earth’s geologic history. •The Geologic Time Scale is a chronological representation of Earth’s geologic history going back 4.6 billion years until present day. •Through fossils scientists can see changes in organisms over time. Environment •Fossils can tell us something about the environment at the time the organism died. •Many times marine fossils are found on mountain tops. •When continental plates collide, it causes uplift. •Finding buried marine fossils suggests the rock layers were once covered by water. Environment •Fossil evidence helps support the Theory of Continental Drift. •Fossils of the same plants and animals were found on different continents now separated by oceans. •These organisms had no way of traveling those distances. •Concluding that the continents were once one supercontinent Rock Cycle
A model that describes the formation, breakdown, and reformation of a rock. Sedimentary Rock •Formed when sediments accumulate and compact and cement together. •Often deposited in layers and contain sand, pebbles, and frequently fossils. •Ex. sandstone, limestone Physical properties of Sedimentary Rocks •Sand, pebble, and even boulder size particles •Some may contain fossils By what process are sedimentary rocks broken down? Weathering •By weather (rain, ice, wind), chemical changes, and living things (plant). •Creates lose material called sediments. By what process are sediments moved? Erosion •Wind •Water •Gravity •Ice They are deposited in layers - Deposition What are the processes that form sedimentary rock? Compaction Sediments are deeply buried, placing them under pressure because of the weight of overlying layers. What are the processes that form sedimentary rock? Cementation •New minerals stick the sediment together just like cement. •This holds the grains together tightly. Metamorphic Rock •Formed by heat and pressure while buried deep below Earth’s surface. •Have a layered or banded (ribbon like) appearance or may have crystals. •Ex. Gneiss, Marble, Slate Physical Properties of Metamorphic Rocks •Layers look like ribbons Crystals What are the processes that form metamorphic rock? Heat (caused by magma) •Temperatures high enough to change its structure but not to melt it. Heat can change sedimentary, igneous, or another older metamorphic rock. What are the processes that form metamorphic rock? Pressure - Caused by intense collisions and friction of tectonic plates and pressure from overlying rock layers. •Deep under the Earth’s surface. •Pressure can change sedimentary, igneous or another older metamorphic rock. Igneous Rock •Formed when lava or magma harden. •Found near volcanoes or fissures •Ex. Basalt, Obsidian, Granite Physical Properties of Igneous rock Fast Cooling Slow Cooling Glassy Large crystals Holes where gas was trapped Many colors What are the processes that form Igneous rock? Melting •Caused by increase in temperature in rock deep below the surface of Earth •Caused by friction between crustal plates What are the processes that form igneous rock? Cooling and Hardening •Melted rock turns solid. •Slow cooling happens below Earth’s surface as magma cools forming large crystals. Ex. granite •Fast cooling happens on the Earth’s surface as lava cools forming small crystals. Ex. obsidian, basalt, pumice |
Erik E. Mason
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