Minerals and Rocks Chapter 10

Minerals and Rocks If you were digging in your yard and found a shiny rock would you think you had found gold or pyrite? Both of these are minerals, and minerals combine to form rocks. Rocks form islands, mountains, valleys, cliffs, and the ocean floor. Rocks you see around you are thousands of years old and may change appearance or location over time.

Minerals Lesson 10.1

Features of Minerals Elements and compounds are called minerals if they have these five features: They are solids. They are formed naturally in the earth. They have the same chemical makeup throughout. They are not alive or made of living things. They have definite arrangement of atoms.

Minerals About 3,000 different minerals are found in the earth. Some are common, but most are rare. Most common minerals: aluminum, quartz feldspar, mica, calcite, dolomite, halite, and gypsum. Some elements are pure elements: gold, sulfur, graphite, diamond. Most elements are compounds (two or more kinds of elements): quartz (silicon and oxygen).

Properties used to Identify Minerals No two minerals share the same properties. Four properties used to identify minerals. Color Luster Streak Hardness

Color Most minerals can be found in more than one color. Quartz (clear, purple, pink, black, or white) Color varies because minerals are not usually found in their pure form. Most minerals contain tiny amounts of other minerals called impurities.

Luster Different minerals reflect light differently. Shiny versus dull. The way that a mineral reflects light is called luster. There are two main kinds of luster: metallic and nonmetallic.

Streak When you rub a soft mineral across a tile it, leaves a mark. The color of the mark is the mineral’s streak. All samples of the same mineral make the same streaks. The streak may be different than the minerals color.

Hardness The hardness of a diamond describes how well the mineral resists being scratched. Geologists measure hardness on a scale of 1-10 (Moh’s scale of hardness). The higher the number on the scale, the harder the mineral. A mineral will scratch any other mineral that has a lower number.

Rocks and Rock Types Lesson 10.2

Rocks and Rock Types About 3,000 minerals occur in the earth. Most are not found in pure form. They are mixed together in rocks. A rock is a solid naturally made of one or more minerals. Only about 20 minerals make up about 95 percent of the earth’s rocks.

Rocks and Rock Types Geologists are interested in how rocks are formed and what they contain. This information helps scientists locate valuable resources, such as oil and metals. Knowledge of rocks is necessary before undertaking construction projects. Rocks provide clues about the history of the earth and how the earth changes.

Rocks and Rock Types Geologists group rocks into three main types, depending on how they form: Igneous rocks form when hot melted minerals cool and harden. Sedimentary rocks form when bits of other rocks and the remains of living things are pressed and cemented together. Metamorphic rocks form when heat, pressure, and chemical reactions change sedimentary or igneous rocks.

The Rock Cycle Rocks are always changing. Some melt deep in the earth, then harden. Some are built by layers of sediment. Some twist and bend because of underground heat and pressure. Each type of rock (igneous, sedimentary, metamorphic) can change into another type. The series of changes that cause one type of rock to become another type of rock is called the rock cycle. The rock cycle occurs over a long period of time.

The Rock Cycle

The Rock Cycle Once on the earth’s surface, all rock types begin to slowly break apart into pebbles and then into fine grains like sand. These grains are easily carried away, often ending up in a large body of water. At the bottom of a lake or ocean, sediment layers form. Over time and under pressure, the layers compact and cement into sedimentary rock. If the sedimentary rock makes it back to the surface the entire process starts again.

The Rock Cycle Other times, sedimentary rock becomes buried deeper in the earth. The rock is exposed to heat and pressure. These underground forces bend and twist it into metamorphic rock. If metamorphic rock is brought to the surface, it begins to break down again.

Rock Cycle Rocks are changed by forces inside the earth and forces on the earth’s surface. Inside the earth: heat and force causes rocks to bend and melt. On the surface: forces such as wind and water cause rocks to break down, move, and settle.