Chapter 2 Section 3 What are minerals? Objectives: Define mineral. Identify and describe some minerals found in Earth’s crust.

Key Term mineral: naturally occurring, inorganic solid formed from elements or compounds and having a definite chemical makeup and regular atomic structure

Earth’s Crust The crust is the outer layer of Earth. It is made up of large chunks of solid rock and smaller pieces of rock, sand particles, and soil. Sand and soil are rock that has been broken into small pieces. All materials in Earth’s crust are made up of elements and compounds.

Earth’s Crust About 75 percent of Earth’s crust is made up of the elements oxygen and silicon. When oxygen and silicon combine, silica is formed. Sand is composed mostly of silica in the form of quartz.

Figure 2-11 Elements found in Earth’s crust

Earth’s Crust Look at figure 2-11. It shows the elements that make up most of Earth’s crust is made up of each element. These elements are found combined into many different compounds.

DESCRIBE: What does Earth’s crust consist of?

Natural Solids A mineral is formed from elements or compounds in Earth’s crust. All minerals are inorganic. This means that they are not formed from living things or from the remains of living things.

Natural Solids A mineral may be either an element or compound. Each mineral has a definite chemical makeup. Gold and silver are example of minerals that are made up of only one element. Mostly, however, minerals are combinations of elements. For example, the mineral quartz is a compound. Quartz is made up of silicon and oxygen. The chemical formulas for some commonly found minerals are shown in Figure 2-12.

SOME MINERALS AND THEIR CHEMICAL FORMULAS Gold Au Calcite CaCO3 Silver Ag Halite NaCl Copper Cu Galena PbS Quartz SiO2 Pyrite FeS2

2. INTERPRET: What are the elements that make up halite?

Rock-Forming Minerals The rocks that make up Earth’s crust are made up of minerals. Scientists have identified more than 2,000 minerals. However, fewer than 20 of these minerals are commonly found in Earth’s crust. These common minerals are called rock-forming minerals. Most rock- forming minerals are compounds.

Rock-Forming Minerals In a rock, the minerals are usually found as mixtures. In a mixture, two or more substances come together. However, the substances do not chemically combine. They retain their original properties. In the case of rocks, each mineral retains its color, texture, and chemical makeup.

3. EXPLAIN: Why are rocks called mixtures?

Metal Minerals Minerals that can be recovered for use are called mineral resources. Aluminum, iron, copper, and silver are some metal minerals. Metals are useful because they can be stretched into wire, flattened into sheets, and hammered or molded without breaking. Tools, machinery, and even the steel girders used in buildings were all made of materials inside Earth’s crust. Metals can be found in many places around the world.

4. NAME: What are some metal minerals?

Classwork CHECKING CONCEPTS About three-fourths of Earth’s crust is made up of oxygen and ___. Quartz is made up mostly of ___. Calcite has ___ atom of calcium for every three atoms of oxygen. Gold is both an element and a ___.

Classwork THINKING CRITICALLY Use figure 2-11 to answer the questions 5 through 8. 5. OBSERVE: Which element makes up almost half of Earth’s crust? 6. IDENTIFY: What are two elements of Earth’s crust that are found in only small amounts? 7. CALCULATE: What percentage of Earth’s crust is made up of iron? 8. SEQUENCE: What five elements make up most of Earth’s crust, from the most common to least?