What is a mineral? What are the characteristics of all minerals?

1. A mineral occurs naturally.

2. A mineral is solid.

3. A mineral has a definite chemical composition.

4. A mineral’s atoms are arranged in a repeating pattern. ( What vocabulary term do you think of when you hear this?)

5. A mineral is inorganic (was never alive)

Is Coal a Mineral? ► We burn coal as a source of energy. It pollutes the air when burned. ► Is coal considered a mineral?

Is Coal a Mineral? ► Miners refer to coal as a “mineral resource” because it is removed from the ground.

Is Coal a Mineral? ► But is it really a mineral? ► (hint: look at the formation of coal and decide; keep the characteristics of a mineral in mind)

Coal ► Coal is referred to as a “mineral resource” ► Coal is not really a mineral because it formed from once-living organisms ► Coal formed from swamp plants ► It takes millions of years for coal to form; this makes it a nonrenewable resource ► Coal is a very important part of Virginia’s economy ► Coal is found predominantly in the Appalachian Plateau physiographic province

Mineral Composition & Groups

Of the almost 4000 known minerals, only about 30 are common. The most common are quartz, feldspar, mica, and calcite.

Minerals ► Quartz and feldspar are the 2 most abundant rock-forming minerals in the Earth’s crust

In fact, over 60% of the Earth’s crust is made up of the family of minerals known as feldspar!

These minerals make up most of the rocks found in the Earth’s crust.

Earth’s Crust ► Earth’s crust is made up of 90 elements. ► 98% of the crust is made up of only 8 elements

Earth’s Crust ► The eight most abundant elements in Earth’s crust are as follows: oxygen(O), silicon(Si), aluminum(Al), iron(Fe), calcium(Ca), sodium(Na), potassium(K), & magnesium(Mg) oxygen(O), silicon(Si), aluminum(Al), iron(Fe), calcium(Ca), sodium(Na), potassium(K), & magnesium(Mg)

Mineral Composition ► Minerals are made up of elements found in the Earth’s crust ► Minerals are in groups based on the elements contained in them

Mineral Groups ► Major groups of minerals are as follows: 1. Silicates 2. carbonates 3.oxides 4. sulfides 5. sulfates 6.halides 1. Silicates 2. carbonates 3.oxides 4. sulfides 5. sulfates 6.halides 7. hydroxides 8. phosphates and 7. hydroxides 8. phosphates and 9. native elements 9. native elements

Silicates ► The silicates are the largest group of rock- forming minerals ► Silicates contain both silicon & oxygen and one or more other elements ► Silicon and oxygen are the 2 most abundant elements in the Earth’s crust ► Pictured:Agate

To be able to identify these and other minerals, we need to look at the properties used to separate and distinguish these minerals.

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

Physical Properties ► Color ► Luster ► Streak ► Hardness ► Specific Gravity

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, sulfur, which is bright yellow, and malachite, which is green.

Many minerals have a similar 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!

Discuss the following! How many of the characteristics of minerals can you name? Why isn’t color a very good property to identify most minerals?

Luster refers to how light is reflected from a mineral. Notice the difference between these two minerals.

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

Terms used to describe nonmetallic luster: Dull, pearly, silky, glassy, and brilliant

Streak of a mineral is the color of its powder when rubbed on a streak plate or an unglazed porcelain tile.

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

Streak ► For example, both gold and pyrite look alike. They appear to be the same thing. ► If you do the streak test, you will discover that gold leaves a yellow streak, whereas pyrite leaves a greenish-black or brown- black streak. ► Pyrite is known as “fool’s gold” because it looks like gold, but is not

Gold & Pyrite

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!

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

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

Calcite and galena cleave in three directions. They are said to have three good cleavages.

Not all minerals show cleavage. Those that break with jagged edges are said to have fracture.

Hardness of a mineral is how easily the mineral can be scratched.

► Friedrich Mohs devised a hardness scale that we refer to as Mohs Hardness Scale. ► In this scale, 10 well-known minerals are given numbers from ► Talc is the softest mineral and a diamond is the hardest mineral

MineralSoftnessTalc1 Gypsum2 Calcite3 Flourite4 Apatite5 Feldspar6 Quartz7 Topaz8 Corundum9 Diamond10 Common Objects HardnessFingernail2.5 Penny3.5 Nail4.5 Glass5.5 Steel File 6.5 Streak Plate 7

► Common objects are used to test the hardness of minerals

Example- Calcite has a hardness of 3 and a copper penny just scratches it because it has a hardness of 3.5

Example: Apatite (left) has a hardness of 5 and can be scratched by a steel knife blade.

Example Quartz (left), with a hardness of 7, is the hardest of the common minerals. It easily scratches hard glass. Quartz is also similar in composition to glass.

Gems are known for their extreme hardness.

Crystal shape can be a useful property to identify minerals if the minerals have had the time and space to form crystals. Most mineral grains that are found in rocks, lack the room to grow.

Specific gravity tells you how many times as dense as water the mineral is. Pure gold can have a specific gravity as high as 19.3!

Calcite is calcium carbonate, CaCO 3. If a drop of weak hydrochloric acid is placed on calcite, the acid bubbles as carbon dioxide is released.

Malleable Magnetic Radioactive Flourescence Taste

Some minerals that contain iron, are magnetic and can be picked up by a magnet. Magnetite is an example of a magnetic mineral.

This is the state of glowing while under a ultraviolet light. Some minerals even glow once the light is turned off!

Some minerals, such as this uraninite, are radioactive. They give off subatomic particles that will activate a Geiger counter.

Halite (rock salt) can be identified by its taste. This practice is not recommended!

Special Properties Of Minerals

Special Properties ► Magnetite is magnetic; lodestone is a type of magnetite ► Calcite fizzes when you put hydrochloric acid on it ► When you look through calcite, you can see a double image ► Sulfur can be identified by its bright yellow color and bad smell

2 Uses of Minerals GemsOres

Gems ► Highly prized because they are rare and beautiful ► Can be cut and polished and used for jewelry ► The brighter and more colorful samples are cut and polished ► Example: amethyst- a form of quartz which has manganese in it to give it its purple color ► Gems are very hard

Ores ► A mineral that is Useful & Profitable ► Waste rock must be removed to get to the desired mineral; removing waste rock is very expensive. ► The value of a mineral can change if the supply of or demand for that mineral changes

Ores & Their Uses ► Examples: ► Bauxite- aluminum ► Hematite- iron ► Galena- lead ► Halite- rock salt ► Graphite- pencil “leads ► Magnetite- iron