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Minerals CH 2 Prentice Hall p. 47-54 What is a Mineral? • A naturally occurring, inorganic solid that has a crystal structure and definite chemical composition. – Over 3,000 – 20 minerals form Earth’s crust. • Rock forming minerals. Naturally Occurring • Must form through Earth’s processes. – Cement, Brick, Steel and Glass all come from substances in Earth’s crust. – But they are manufactured by people. Inorganic • Cannot come from materials that were once part of living things. – Coal- forms naturally, comes from the remains of plants and animals. Solid • Always solid, with a definite volume and shape. – Particles can’t flow freely. Crystal Structure • Particles of a mineral line up in a repeating pattern. Forms a solid called a crystal. – Has flat sides called faces, that meet at sharp edges and corners. Definite Chemical Composition • A mineral always contains certain elements in definite proportions. • Element- a substance composed of a single kind of atom. – All atoms have the same chemical and physical properties. Definite Chemical Composition • Compound- Two or more elements combined. – Most minerals are compounds. – Chemically joined. Definite Chemical Composition • Mixture- consists of two or more substances that are mixed together but not chemically combined. Crystal Structure • Each mineral grows atom to atom to form that mineral’s particular structure. – Classified into six groups (crystal systems) based on the number and angle of the crystal faces. Identifying Minerals Identifying Minerals Color Cleavage/Fracture Streak Hardness Luster Density Crystal Systems Special Properties Color • 1. Color is an easily observed physical property. Not the best property to use to identify because many minerals like quartz can come in a variety of colors. Identifying Minerals Streak • Streak is the color of the minerals powder when it is rubbed against a Streak Plate – This property does not vary like the color of the mineral can. Identifying Minerals Luster • Luster is used to describe how a mineral reflects light from its surface. • Metallic luster- looks like a metal. • Non-Metallic Lusterdoes not look like a metal, can be glassy, dull, earthy, waxy and pearly. Identifying Minerals Crystal Structure • Each mineral grows atom to atom to form that mineral’s particular structure. – Classified into six groups (crystal systems) based on the number and angle of the crystal faces. Identifying Minerals Crystal Structure • Particles of a mineral line up in a repeating pattern. Forms a solid called a crystal. – Has flat sides called faces, that meet at sharp edges and corners. 5. Cleavage • Cleavage- is a mineral that easily splits along flat surfaces. Identifying Minerals 6 Fracture • Fracture- describes how a mineral looks when it breaks apart in an irregular way. Identifying Minerals Special Properties • Fluorescence- glows under UV (ultraviolet light) • Magnetic- acts like a magnet • Radioactive- give off radiation- Uraninite • Reacts to Acid- reacts by fizzing. • Electrical Properties- electric current can be produced (Quartz) – Used in watches Identifying Minerals Hardness • The resistance to being scratched. One of the best clues. • Mohs hardness scale. – A scale from 1 to 10. Identifying Minerals Mohs Hardness Scale see p150 to label s boxes with minerals 1. 2. Softest known mineral. It flakes when scratched by a fingernail. 4. A steel nail can easily scratch it. 7. Can scratch steel and hard glass easily. 3. A fingernail can easily scratch it. 5. Other Hardness’s A fingernail cannot scratch it, but a copper penny can. 6. A steel nail can scratch it. 8. Cannot be scratched by a steel nail, but it can scratch window glass. 9. Can scratch quartz. 10. Can scratch topaz. Hardest known mineral, Diamond can scratch all other surfaces. Identifying Minerals Density • It is the mass in a given volume. • It always remains the same for any given mineral. Identifying Minerals Density • A balance would be used to measure the mass of a sample. • The sample can be placed in a graduated cylinder to determine the volume. Identifying Minerals Density • Water Displacement (how much water is moved, is equal to the volume of the sample) is used to determine the volume of the sample Identifying Minerals