Minerals of the Earth’s Crust

Georgia Performance Standards S6E5. Students will investigate the scientific view of how the earth’s surface is formed. b. Investigate the contribution of minerals to rock composition.

What is a mineral? Is naturally occurring Is a solid Is inorganic (mostly) Has a fixed chemical formula Has an orderly crystalline structure

Naturally Occurring To be considered a mineral it must have been formed by natural geologic processes. Laboratory created gems (synthetic diamonds, rubies, etc.) don’t count.

A Solid By definition, minerals are solid within the normal temperature ranges of the earth’s surface.

Inorganic Generally, a mineral is a naturally occurring solid with a crystalline structure. However, Halite (table salt) is a mineral. Sugar is a crystalline, but it comes from plants. Therefore, it is organic. Coal comes from plants but is considered a mineral.

Elements and Atoms Elements are pure substances that cannot be broken down into simpler substances by ordinary chemical means. There are 92 naturally occurring elements. Each element is made of only one kind of atom. An atom is the smallest part of an element that has all properties of that element. For example: Gold (Au)

Compounds A compound is a substance made of two or more elements that have been chemically joined, or bonded. For example: Halite (table salt) is NaCl or Sodium Chloride Quartz is SiO2 or Silicon Oxide

Orderly Crystalline Structure Solid geometric forms of minerals produced by a repeating pattern of atoms or molecules that is present throughout the mineral are called crystals. The mineral gold is composed of gold atoms arranged in a crystalline structure. The arrangement of gold atoms form the shape of a gold crystal.

Two Groups of Minerals Silicates (make up more than 90% of the Earth’s crust) Native Elements Sulfides Oxides Carbonates Sulfates Halides Nonsilicate Minerals Minerals can be divided into Silicates and non silicates.

Silicates Minerals that contain a combination of silicon and oxygen. Silicon and oxygen are the two most common elements in the Earth’s crust. Silicon and oxygen usually combine with other elements such as aluminum, iron, magnesium, and potassium. Quartz, a type of silicate, is the basic building blocks of many rocks.

Native Elements Native Elements is the category of the pure. Most minerals are made up of combinations of chemical elements. In this group a single element like copper are found in a naturally pure form. Silicon is a metallic element used to make computer chips and other electronic equipment. Although it is the second most abundant element in the world it was not discovered until 1824.

Sulfides Sulfides are made up of sulfur compounds with another mineral, usually a metal. Many of the world’s primary metal ores belong to this group. Sulfide minerals are used to make batteries, medicines, and electronic parts.

Oxides Oxides are mineral compounds combining a metal with oxygen or a metal combining with oxygen and hydrogen. This is a large group of minerals that occur in most geological environments and rock types. Oxide minerals are used to make abrasives, aircraft parts, and paint.

Carbonates Minerals that contain combinations of carbon and oxygen in the chemical structure. We use carbonate minerals in cement, building stones, and fireworks.

Sulfates Minerals that contain sulfur and oxygen, SO4. Sulfates are used in cosmetics, toothpaste, cement, and paint.

Halides Compounds that form when fluorine, chlorine, iodine, or bromine combine with sodium, potassium, or calcium. Halide minerals are used in the chemical industry and in detergents.

Ticket Out the Door In your own words write a definition for each of the following terms: element compound mineral Link provides a good review of the types of minerals Silicate and non silicate minerals

Identifying Minerals Color Luster Streak Cleavage or Fracture Hardness Density Special Properties

Identifying Minerals Rarely is a mineral identified by a single property. These properties need to be considered together to correctly identify a mineral.

Color Color is the most easily observed mineral property and the least useful! Some exceptions to the color rule would be cinnabar, which is always red, and malachite, which is green.

Color Many minerals have a similar color.

Color Many minerals can turn colors due to impurities, or they can change colors in various circumstances. For example: pure quartz is colorless or white, impurities can make the mineral rose, purple or pink!

Luster Luster refers to the way a mineral shines in reflected light. Notice the difference between these two minerals?

Luster The mineral on the left has a metallic luster, the one of the right, a nonmetallic luster.

Types of Luster Metallic: bright, reflective Submetallic: dull, reflective Vitreous: glassy, brilliant Silky: fibrous Resinous: plastic Waxy: greasy, oily Pearly: creamy Earthy: rough, dull

Streak Streak of a mineral is the color of its powder when rubbed on an unglazed white tile.

Streak The streak is often not the same color as the mineral. A minerals color may vary, but the streak rarely will!

Cleavage The cleavage of a mineral is its tendency to split easily or to separate along flat surfaces. Cleavage can even be observed on tiny mineral grains making it a very useful property!

Cleavage Mica is probably the best example as it splits into thin sheets. It is said to have one perfect cleavage.

Cleavage Feldspar splits readily in two directions, always at or near right angles.

Cleavage Not all minerals show cleavage. Those that don’t break along cleavage surfaces are said to have fracture.

Hardness The hardness of a mineral is its resistance to being scratched. Diamond is the hardest of all minerals, and talc is the softest.

To determine hardness, scientists use Mohs hardness scale. Friedrich Moh (1773-1839): German geologist and mineralogist

Mohs Hardness Scale Measures hardness on a scale from 1 (lowest) to 10 (highest). To determine the hardness of a mineral you must try to scratch the mineral against a glass plate.

Mohs Hardness Scale Talc: baby powder (soft pencil will scratch) Gypsum: sheetrock (finger nail “”) Calcite: cements (penny) Fluorite: toothpaste (iron or brass nail) Apatite: fertilizer (steel knife blade) Feldspar: floor tiles (will scratch a window glass) Quartz: watches, abrasives (scratches hard glass or steel) Topaz: gemstone (emerald) (scratches quartz) Corundum: gemstone (ruby & sapphire) (scratch topaz) Diamond: saw blades (easily scratches the rest of the minerals)

Density Each mineral has a specific density. Density is the mass of a given space or in scientific terms the mass per unit of volume. For Example: If you have two minerals of the same size one might be heavier than the other. The galena will be three times heavier than the same size of quartz.

Density Geologists measure density by the following: First they use a balance to determine the mass of a sample. Second, they place the mineral in water to see how much water it displaces. The volume of displace water = the volume of the sample Third they use the following formula: Density = Mass/Volume

Review

Some Llamas Climb Down Funny Hills Review Some Llamas Climb Down Funny Hills Streak Powdered Color Luster How shiny Cleavage Breaks in sheets or blocks Density How much mass in a given volume Fracture Just crumbles & breaks Hardness Can be scratched by

Special Properties Fluorescence Chemical Reaction Optical Properties Magnetism Taste Radioactivity

Fluorescence Calcite and fluorite glow under ultra violet light.

Chemical Reaction Calcite will become bubbly or “fizz,” when a drop of weak acid is placed on it.