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Minerals, Rocks, and Soils. What is a rock? Why is gold so expensive compared to iron? Why do plants grow in some areas but not others?. Activity. With a partner, examine the items given to you. Decide how you might classify the items.
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What is a rock? • Why is gold so expensive compared to iron? • Why do plants grow in some areas but not others?
Activity • With a partner, examine the items given to you. Decide how you might classify the items. • What does an item’s hardness tell you? Should all of the “hard” items be classified as rocks? Are all rocks hard? What other observations can you make about each item? • Discuss what makes a rock a rock. Record your observations.
Minerals • In the last activity you examined a number of items and decided which items could be classified as rocks. • What is a rock? • Rock is made up of one or more pure, naturally occurring, non-living solid materials called minerals.
Stuff You Should Know • Although glass is made up of the same elements as quartz, it is not a solid, so it is not a mineral. • Glass is like a very thick liquid that flows extremely slowly! • If you examine glass windows in older building you will notice that the glass is thicker at the bottom because gravity has pulled the liquid downward!
Most minerals are quite rare. A few are common and can be found throughout Earth’s crust (the thin outermost layer). • A mineral is an inorganic, naturally occurring solid material that can be an element (a pure substance) or a compound (two or more substances). • Quartzxample: quartz consists of silicon and oxygen
As you have already discussed many rocks can be scratched with your fingernail while others are quite hard. • The substance’s “scratchability” can also be a great way to classify the sample. • German scientist, Friedrich Mohs, developed a scale of ten minerals with a “hardness” value of 1 to 10.
Friedrich Mohs • Carl Friedrich Christian Mohs (29 January 1773 – 29 September 1839) was a German geologist and mineralogist.
The Mohs Hardness Scale is a useful tool for mineral identification. • Given that there are over 3000 minerals, other properties are needed to identify them. • Minerals sometimes occur as crystals. • A crystal occurs naturally and has straight edges, flat sides, and regular angles.
Other Clues for Mineral Identification • Lustre – The “shininess” of the mineral depends on how light is reflected from its surface.
Colour – One of the more attractive properties of minerals. Although popular to use it can be difficult to rely just on colour to identify a mineral.
Streak – Streak is the colour of the powdered form of the mineral. Some minerals may appear dark in colour but their streak is very light.
Cleavage and Fracture – If a mineral breaks along smooth, flat surfaces, it is said to have cleavage. If a mineral breaks with a rough or jagged edges it has fracture.
Uses of Minerals • As we have discussed, minerals have many properties that make them valuable, but what makes them useful?
Diamonds, because they are the hardest of the minerals, have many uses. Diamonds can be used as the tips of drill bits and can also be used in cutting through hard materials such as steel and rock.
Find out your birthstone and research it’s properties and uses. Is it rare? Is it expensive? What interesting facts did you find out?
Metals are among the most useful minerals. Many of our day-to-day items contain minerals like metals. Cars, electronics, and appliances all contain metals. • Metals are single elements, such as gold, silver, copper, aluminum, nickel and iron.
Geologist’s Mystery • See page 284 - 285
Metals occur naturally in rocks, where they are mixed with other mineral deposits. • Rocks that are rich in metals and metal oxides are called metallic ores.
Minerals and You • In order for people to live and grow they need minerals. • In order to survive, your body needs over 20 different kinds of elements found in minerals. Can you name any?
Rocks and the Rock Cycle • As mentioned earlier, rocks are made of minerals. Next we will look at how minerals are formed. • There are three major families of rocks based on how they are formed. • Igneous • Sedimentary • Metamorphic
Igneous Rock • “Igneous” comes from the Latin word meaning “fire”, what English word is similar to “Igneous” and has to do with fire?
Igneous rock forms when hot magma or lava cool and solidify. • Magma is melted rock found below the Earth’s crust, where temperatures and pressures are high.
Magma can push away or dissolve surrounding rock, making room. Eventually this magma cools and eventually forms what is called intrusive rock. Granite is an example of Igneous rock.
When magma breaks through the Earth’s crust, in the form of a volcanic eruption, it is called lava.
Rock that forms when lava cools on the Earth’s crust is called extrusive rock.
Igneous rocks contain randomly arranged interlocking crystals. The size of the crystals depends on how quickly the molten magma solidified. The more slowly the magma cools, the bigger the crystals.
Sedimentary Rock • Sedimentary rock is made from sediment. Sediment is loose material, such as bits of rock, minerals, and plant and animal remains.
Sedimentary rock makes up about 75% of the rock we see on the Earth’s surface.
As sediment settles on the land, usually at the bottom of lakes and oceans, it slowly settles in layers. These layers are called beds.
The sedimentary beds are formed over long periods of time as the pressure from layer and layer of sediment press down on other sediment. This process is called compaction.
The compression squeezes out water, leaving salt crystals that cement the rocks together. The crystals form a sort of glue that sticks or cements the pieces of rock together. This process is called cementation.
Limestone is a very common type of sedimentary rock and unique because fossils are often found in samples. • Fossils are the remains of once-living organisms. • Because of this phenomenon, limestone is classified as organic sedimentary rock.
Metamorphic Rock • Earth movements can cause rocks to be deeply buried or squeezed. As a result, the rocks are heated and put under great pressure. They do not melt, but the minerals they contain are changed chemically, forming metamorphic rocks.
The type of metamorphic rock depends on the amount of pressure applied. • Metamorphic means “change form”. • Shale can undergo several changes in form as pressure and temperature change increase over time. The shale changes to slate to schist to gneiss.
Metamorphic rocks sometimes contain fossils if they were formed from a sedimentary rock, but the fossils are usually squashed out of shape. • Metamorphic rocks can be formed from any other type of rock - sedimentary or igneous. • slate is formed from shale • marble is formed from limestone
The Rock Cycle • So far we’ve learned that rocks are constantly changing over long periods of time. • These changes happen in other ways from what we just learned.
Weathering • Rocks gradually wear away. This is called weathering. There are three types of weathering: • Physical or mechanical weathering • chemical weathering • biological weathering
Physical Weathering • Physical weathering is caused by physical changes such as changes in temperature, freezing and thawing, and the effects of wind, rain and waves.
Freeze-Thaw or Frost Wedging • Water expands slightly when it freezes into ice. This is why water pipes sometimes burst in the winter. • The formation of ice can also break rocks. If water gets into a crack in a rock and then freezes, it expands and pushes the crack further apart. When the ice melts later, water can get further into the crack. When the rock freezes again, it expands and makes the crack even bigger. • This process of freezing and thawing can continue until the crack becomes so big that a piece of rock falls off.
This process of freezing and thawing can continue until the crack becomes so big that a piece of rock falls off.
This process of freezing and thawing can continue until the crack becomes so big that a piece of rock falls off.
This process of freezing and thawing can continue until the crack becomes so big that a piece of rock falls off.
This process of freezing and thawing can continue until the crack becomes so big that a piece of rock falls off.
Wind, Rain and Waves • Wind, rain and waves can all cause weathering. The wind can blow tiny grains of sand against a rock. These wear the rock away and weather it. Rain and waves can also wear away rock over long periods of time.
