Characteristics of Minerals Chapter 2 Characteristics of Minerals

What is a Mineral? In your notebook, write what you think a mineral is. Share your answer with a table partner. What are some of your ideas?

Minerals Have Four Characteristics Forms in nature Is a solid Has a definite chemical makeup Has a crystal structure

Mineral or Rock? Minerals must have all four characteristics, while rocks have only two of them. Rocks are solids and they form naturally.

Formed in Nature Every type of mineral can form in nature without help from living organisms. Some form through evaporation (halite), some form when molten rock cools (granite), some form due to temp/pressure changes (talc).

Solid They all have a definite volume and rigid shape. Liquid water is not a mineral, but ice is.

Definite Chemical Makeup They consist of a specific combination of atoms of certain elements. An element is a substance that contains only one type of atom. Most minerals are compounds: substances consisting of different elements in specific proportions. The type and bonds of the atoms makes minerals unique.

Definite Chemical Makeup

Crystal Structure Crystal: a solid in which the atoms are arranged in an orderly, repeating 3-D pattern. Sometimes, two minerals have the same chemical composition, but the way the atoms bond changes their crystal structure. Both diamond and graphite are made of carbon, but they are very different because of their internal structure.

Crystal Structure

Crystal Structure Perfect crystals are extremely rare in nature because they often do not have enough open space. Copy the names of the 6 crystal groups (shapes) on page 47 with the example given in the book.

Chapter 2 Grouping Minerals

How are They Grouped? Scientists group them based on their chemical makeup.

The Silicates The most common group of minerals. Contain oxygen and silicon joined together. Make up 90% of the rocks in Earth’s crust. Examples: quartz, feldspar, and mica.

The Carbonates The second most common group of minerals. Contain oxygen and carbon joined together. Example: calcite

The oxides Contain oxygen and a metal joined together. Example: hematite

Chapter 2 Mineral’s Appearance

Identifying Unknown Crystals There are certain characteristics that we should look at when trying to identify crystals.

Color Some crystals are found in nature to be many different colors. What causes these changes in color? Tiny amounts of an element that is not part of its normal chemical makeup. Location: contact with air or water on Earth’s surface can change crystals. Defects in the chemical structure.

Color

Streak Streak is the color of the powder left behind when the mineral is scraped against a surface. All samples of the same mineral have the same streak left behind. Better indicator than surface color.

Luster Luster is the way in which light reflects from a mineral’s surface. Two main types: metallic and nonmetallic.

Chapter 2 A Mineral’s Break

Using Break to Identify Minerals All minerals break in a specific way, and all samples of that type of mineral will break that way. The way it breaks depends on the atom arrangement.

Cleavage Cleavage: the tendency of a mineral to break along flat surfaces. The bonds between the atoms are less strong in some directions than in others.

Fracture Fracture: the tendency of a mineral to break into irregular pieces. The bonds between the atoms are equal in strength in all directions.

Chapter 2 Density and Hardness

Density Density: the amount of mass in a given volume of the substance. Determined by the kinds of atoms that are in the mineral, and how closely they are joined together.

Density Gold and pyrite look very similar, but they have very different densities. Gold has a much higher density.

Hardness Hardness: a mineral’s resistance to being scratched. Determined by its crystal structure and the strength of the bonds between its atoms. Measured on the Mohs scale.

Mohs Scale A harder mineral will scratch a softer one. Talc is the softest at 1, diamond is the hardest at 10.

Mohs Scale To test unknown minerals, see whether it is scratched or can scratch other minerals. If you can scratch an unknown mineral with quartz but not with feldspar, then it is somewhere between a 6 and 7 and on the hardness scale.

Chapter 2 Special Properties

Reactivity Minerals in the carbonate group react when mixed with an acid.

Fluorescence These minerals glow when they are exposed to ultraviolet light.

Magnetism Radioactivity These minerals are attracted to magnets They contain unstable elements that change into other elements over time. Radioactivity

Chapter 2 Mineral Formation

Water Evaporates Many substances dissolve in water. When the water evaporates, the mineral deposits are left behind. Halite and gypsum.

Hot Water Cools Hot water can dissolve minerals from rocks. The minerals can move through the rocks, but when they cool, they return to solids. Sometimes when they cool, they form new minerals because the atoms are arranged differently.

Molten Rock Cools Magma: molten rock inside Earth; lava: molten rock that reaches Earth’s surface. When the magma/lava cools, minerals are formed.

Heat and Pressure Heat and pressure can cause bonds between atoms to break. When they join back together, they may form different minerals.

Organisms Produce Minerals Ocean animals produce calcite and other carbonate minerals. Humans produce apatite.

Chapter 2 Mineral Uses

Uses in Industry Metal for cars/planes Glass Toothpaste Photographic film Paint

Uses in the Arts Birthstones/gems/jewelry

Mining Before we can use minerals, they must be taken from the ground. Rocks that contain enough of a mineral to be mined for a profit are called ores.

Surface Mining Mining minerals at or near the surface. Dense minerals build up in riverbeds and can be recovered by panning.

Surface Mining Strip mining: miners strip away plants, soil, and unwanted rocks from the surface. Open-pit mining: removing the surface layer of soil. Explosives are used to break up the underlying rock.

Deep Mining Miners dig, blast, drill, and cut ore out of deeper layers of Earth’s surface, hills, and mountains.