Presentation on theme: "6.E.2.3 Explain how the formation of soil is related to the parent rock type and the environment in which it develops."— Presentation transcript:
6.E.2.3 Explain how the formation of soil is related to the parent rock type and the environment in which it develops.
What is a mineral? Suppose you are planning an expedition to find minerals. Where would you look? You can find minerals in your home—in the salt shaker and in your pencil.
Metal pots, glassware, and ceramic dishes are products made from minerals. Minerals and products made from them surround you.
A Mineral is a naturally occurring, inorganic solid that has a crystal structure and a definite chemical composition. Inorganic means they usually are not formed by plants or animals. You could go outside and find minerals that occur as gleaming crystals—or as small grains in ordinary rocks. The particular chemical makeup and arrangement of the atoms in the crystal is unique to each mineral. Rocks are usually made of two or more minerals.
How Do Minerals Form? Minerals form in several ways: * One way is from melted rock material inside Earth called magma. As magma cools, atoms combine in orderly patterns to form minerals. Minerals also form from magma that reaches Earth’s surface. Magma at Earth’s surface is called lava.
* Evaporation can form minerals. Just as salt crystals appear when seawater evaporates, other dissolved minerals, such as gypsum, can crystallize. * A process called precipitation can form minerals, too. Water can hold only so much dissolved material.
Formation Clues Sometimes you can tell how a mineral formed by how it looks. Large mineral grains that fit together like a puzzle seem to show up in rocks formed from slow cooling magma. If you see large, perfectly formed crystals, it means the mineral had plenty of space in which to grow. This is a sign they may have formed in open pockets within the rock. To figure out how a mineral was formed, you have to look at the size of the mineral crystal and how the crystals fit together.
Properties of Minerals Each mineral, too, has a set of physical properties that can be used to identify it. With a little practice you can learn to recognize mineral shapes and use its properties to help you identify the type mineral. All minerals have an orderly pattern of atoms. The atoms making up the mineral are arranged in a repeating pattern.
Properties of Minerals (Cont.) Geologists have identified about 3,800 minerals. Telling them apart can be a bit of a challenge. Each mineral has characteristic properties that can be used to identify it. When you have leaned to recognize the properties of minerals, you will be able to identify many common minerals around you. To observe properties of a mineral you need to conduct tests on the sample.
Identifying Minerals Color The color of a mineral is an easily observed physical property. But the color of a mineral alone often provides too little information to make an identification. Color can be used to identify only those few minerals that always have their own characteristics. Ex.) malachite = green azurite = blue
Streak A streak test can provide a clue to a mineral’s identity. The streak of a mineral is the color of its powder. You can observe a streak by rubbing a mineral against a piece of unglazed porcelain tile. The color of a mineral may vary; however, its streak does not. Surprisingly, the streak color and the material color are often different. Ex.) Pyrite = gold color = greenish black streak Gold = gold color = golden yellowish streak
Luster Luster describes how light reflects from a mineral’s surface. If it shines like a metal, the mineral has metallic luster. Nonmetallic minerals can be described as having pearly, glassy, dull, silky, or earthy luster. You can use color, streak, and luster to help identify minerals.
Density Each mineral has a characteristic density. Recall that density is the mass in a given space, or mass per unit volume. No matter what the size of a mineral sample, the density of that mineral always remains the same. You can compare the density of two material samples of about the same size. Density = Mass/Volume
Hardness One of the best clues for a identifying a mineral is by its hardness. In 1812, Friedrich Mohs, an Austrian mineral expert, invented a test to describe the hardness of minerals. Called the Mohs hardness scale, this scale ranks ten minerals from softest to hardest. Hardness can be determined by a scratch test. A mineral can scratch any mineral softer than itself, but can be scratched by any mineral that is harder.
Cleavage and Fracture Another clue to a mineral’s identity is the way it breaks. Minerals that split into pieces with smooth, regular planes that reflect light are said to have cleavage. Cleavage is caused by weaknesses within the arrangement of atoms that make up the mineral. Not all minerals have cleavage. Some break into pieces with jagged or rough edges. Instead of neat slices, these pieces are shaped more like hunks of cheese torn from an unsliced block. Materials that break this way, such as quartz, have what is called fracture.
Minerals in the mica group have one direction of cleavage and can be peeled off in sheets. Fracture can be jagged and irregular or smooth and curvy like in flint. Cleavage Fracture
Crystal Systems The crystals of each mineral grow atom by atom to form that mineral’s particular crystal structure. Geologists classify these structures into six groups based on the number and angle of the crystal faces. Sometimes the crystal structure is obvious form the mineral’s appearance. Sometimes the structure is visible only under a microscope. A few minerals are still considered minerals even though their particles are not arranged in a crystal structure.
Special Properties Some minerals can be identified by special properties such as: magnetism, fluorescence, reactivity (reacts chemically to acids), optical (bends light), and electrical (can transmit an electric current). Read pages from your science textbook
Questions: Because minerals do not come from once—living material, they are said to be A. crystalline. B. solid. C. colorful. D. inorganic.
In a mineral, the particles line up in a repeating pattern to form a(n) A. element. B. crystal. C. mixture. D. compound.
Which characteristic is used to determine the color of a mineral’s powder? A. luster B. fracture C. cleavage D. streak
Which is true of all minerals? A. They are inorganic solids. B. They have a hardness of 4 or greater. C. They have a glassy luster. D. They can scratch a penny.