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EARTH’S STRUCTURE Chapter 2: Minerals and Rocks 2.1 Properties of Minerals What is a Mineral? • Mineral: a naturally occurring solid that can form by inorganic processes and that has a crystal structure and a definite chemical composition. • Let’s break this down --- What is a Mineral? • Mineral: a naturally occurring solid that can form by inorganic processes and that has a crystal structure and a definite chemical composition. • This means that minerals are formed by natural processes in and on Earth. What is a Mineral? • Mineral: a naturally occurring solid that can form by inorganic processes and that has a crystal structure and a definite chemical composition. • This means that minerals are all solid, with a definite volume and shape. • The particles are packed together tightly. What is a Mineral? What is a Mineral? • Mineral: a naturally occurring solid that can form by inorganic processes and that has a crystal structure and a definite chemical composition. • This means that minerals are formed from items that were not a part of a living organism. What is a Mineral? • Mineral: a naturally occurring solid that can form by inorganic processes and that has a crystal structure and a definite chemical composition. • A crystal is a repeating pattern of flat sides (faces) that meet at sharp edges and corners. What is a Mineral? What is a Mineral? • Mineral: a naturally occurring solid that can form by inorganic processes and that has a crystal structure and a definite chemical composition. • A mineral always contains the exact chemical structure – the same elements are present in the same proportions. What is a Mineral? Minerals, Compounds, & Elements • Almost all minerals are compounds. • Compound: two or more elements that are combined so that the elements no longer have their own properties. • Each mineral has a unique combination of elements. • Some elements, like copper, silver, and gold, are also minerals. Identifying Minerals • Color: • Many minerals share the same color • Not a great way to identify the minerals Identifying Minerals • Streak: • Color of the powder left behind from the mineral • The streak is not always the same color as the mineral Identifying Minerals • Luster: • How light is reflected from a mineral’s surface • Metallic, glassy, earthy, silky, waxy, and pearly Identifying Minerals • Hardness: • One of the most useful ways to identify minerals • Mohs Hardness Scale ranks minerals from 1-10, with 10 being the hardest (Diamond) and 1 being the softest (Talc). • Determined by a scratch test – scratch unknown mineral by known minerals to see if a scratch appears or not. Identifying Minerals • Density: • Unique to each mineral • Mass divided by volume • Depends on how the atoms are arranged in the mineral Identifying Minerals • Crystal Structure: • All crystals in a mineral have identical patterns • Good to identify small samples • Beams reflect light in specific patterns Identifying Minerals • Cleavage and Fracture: • Cleavage: a mineral that splits easily along flat surfaces; depends on how the crystals are arranged. • Fracture: a mineral breaks apart in an irregular way Identifying Minerals • Special Properties: • Magnetism • Glow in UV light • Bends light • Conducts electricity CHAPTER 2: MINERALS AND ROCKS 2.2 Classifying Rocks Classifying Rocks • About 20 minerals make up most of the rocks on Earth’s crust. • These are called rock-forming minerals. • A rock’s color gives clues to the minerals that make it up. • Granite is usually light colored and rich in oxygen and silica, while basalt is generally dark colored with a low silica content. Classifying Rocks Texture • Grains give the rock its texture, the look or feel of a rock’s surface. • Grain size: rocks with large grains are coarse grained, rocks with small grains are fine-grained rocks. Texture • Grains give the rock its texture, the look or feel of a rock’s surface. • Grain shape: rounded grains form a conglomerate rock, jagged grains form breccia. Texture • Grains give the rock its texture, the look or feel of a rock’s surface. • Grain pattern: patterned layers of grains form a banded rock, while rocks with no patterns are non-banded. Rocks • There are three main types of rocks: • Igneous: forms from the cooling of magma/lava. • Sedimentary: forms when small particles are pressed and cemented together. • Metamorphic: forms when an already existing rock is changed by heat, pressure, or chemical reactions. CHAPTER 2: MINERALS AND ROCKS 2.3 Igneous Rocks Igneous Rocks • These rocks are classified by their: • Origin • Texture • Mineral composition Origin • Igneous rocks can form below or above ground. • If they are formed below ground, they are made of magma and are said to be intrusive. • Granite is the most abundant intrusive rock. • If they are formed above ground, they are made of lava and are said to be extrusive. • Basalt is the most common extrusive rock. Origin Texture • Texture depends on the size and shape of its mineral crystals. • Rapidly cooling lava forms fine-grained igneous rocks with small crystals or no crystals. (extrusive) • Slow cooling magma forms coarse-grained rocks with large crystals. (intrusive) Mineral Composition • Lava low in silica usually forms dark rocks. • Magma high in silica usually forms light rocks. Uses for Igneous Rocks • Because they are hard, dense, and durable, igneous rocks are used for tools and building materials. CHAPTER 2: MINERALS AND ROCKS 2.4 Sedimentary Rocks Sedimentary Rocks • Sediment is small, solid pieces of material that come from rocks or living things. • Processes like weathering, erosion, deposition, compaction, and cementation help form sedimentary rocks. Sedimentary Rocks • Weathering: the breaking apart/wearing down of • • • • materials. Erosion: the movement of sediment Deposition: the depositing, or laying down, or sediment. Compaction: the process that presses sediments together. Cementation: the process in which dissolved minerals crystallize and glue sediments together. Sedimentary Rocks • There are three main groups of sedimentary rocks: • Clastic rocks • Organic rocks • Chemical rocks Clastic Rocks • A sedimentary rock formed when rock fragments are squeezed together. • Grouped by the size of the rock fragments • Examples: shale, sandstone, conglomerate, and breccia. Organic Rocks • Forms where the remains of plants and animals are deposited in layers. • Coal forms from swamp plant remains. • Limestone forms in the ocean from animals with shells made of calcite. Chemical Rocks • Forms when minerals dissolved in a water solution crystallize. • Sometimes these are formed from mineral deposits in seas/lakes that evaporate. • Such as halite (rock salt) • Limestone is an example of this when calcite is dissolved and crystallizes. Uses for Sedimentary Rocks • Again, many types of sedimentary rocks are used for tools and building. CHAPTER 2: MINERALS AND ROCKS 2.5 Metamorphic Rocks Metamorphic Rocks • Any rock that forms from another rock as a result of changes in heat or pressure or both is called metamorphic. Classifying Meta. Rocks • Foliated Rocks: • When grains are arranged in parallel layers or bands in the rock. • Slate is an example; formed from shale. Classifying Meta. Rocks • Non-foliated Rocks: • The grains in these rocks are arranged randomly. • Quartzite forms from quartzite sandstone. • Marble forms from limestone. Using Meta. Rocks • Marble is great for sculpting into different shapes, so it is used in statues and buildings. • Slate is also used in many building structures because it splits into layers easily. CHAPTER 2: MINERALS AND ROCKS 2.6 The Rock Cycle The Rock Cycle • Series of processes that occur in and on Earth to slowly change rocks from one kind to another. • There is no set pathway for rocks to follow. The Rock Cycle • The changes that rocks go through are related to plate tectonic activity. • Plate movement helps to form and move magma, mountains, and other structures. • Materials are not lost during the change, they are just transformed. The Rock Cycle The Rock Cycle