Aim: How can we describe a mineral?

Turn and Talk Take one minute with your partner next to you and discuss what you think a mineral is.

Minerals

So what is a mineral? A mineral must meet the following five characteristics. All rocks are made of minerals What are the 5 characteristics of all minerals?

Mineral Characteristics

1. A mineral occurs naturally.

2. A mineral is solid.

3. A mineral has a definite chemical composition.

3. A mineral has a definite chemical composition. Find the ESRT page that deals with minerals. What is the composition of halite? Quartz

TTYP What are the two most common elements in all minerals?

Average Crustal Composition What two elements are the most abundant by mass in the crust? Oxygen Silicon

4. A mineral’s atoms are arranged in an orderly pattern.

5. A mineral is inorganic (was never alive)

Mineral or Not? Gold Water Pearls

Mineral or Not? Coal Diamond Silver

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

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

Minerals are arranged into groups… According to their chemical and physical properties.

Mineral Groups Silicates Other groups include: The most common (silicon & oxygen) Other groups include: Carbonates Sulfides Oxides Halides Hydroxides Sulfates The molecular structure is called a silica tetrahedron

The importance of Minerals Without a proper intake of zinc the immune system can become vulnerable and normal human growth can be delayed. Zinc also plays a key role in our ability to heal wounds

Turn and Talk With your partner look at p. 16 of your reference table and find some common uses for minerals.

Identification of Minerals

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!: You cannot identify a mineral only using one property. These properties need to be considered together to correctly identify a mineral.

1. Color What color the mineral is. Color is the most easily observed mineral property and the least useful!

Many minerals have a similar color.

Colors Many minerals can turn colors due to impurities, or they can change colors in various circumstances.

Color For example, pure quartz is colorless or white, impurities can make the mineral rose, purple or pink!

Some exceptions to the color rule would be cinnabar, which is always red, and malachite, which is green.

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

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

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

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

Metallic or Non-metallic? Galena

Metallic or Non-metallic? Quartz

Metallic or Non-metallic? Pyrite aka fool’s gold

4. Hardness The hardness of a mineral is its resistance to being scratched. Diamond is the hardest of all minerals, and talc is the softest. The harder one will always scratch the softer one

Common hardness tests Unpolished finger nail = 2.5 Steel = 4.5 Glass = 5.5

4. Hardness Friedrich Mohs devised a hardness scale. In this scale, ten well known minerals are given numbers from one to ten. Lets take a look at the ten minerals used and some of the simple tests.

Hardness Talc (left) is the softest and has a hardness of 1. A soft pencil lead will scratch talc. Gypsum is a bit harder and has a hardness of 2. A fingernail scratches gypsum.

Hardness Calcite (left) has a hardness of 3 and a copper penny just scratches it. Fluorite has a hardness of 4 and it can be scratched by an iron or brass nail.

Feldspar has a hardness of 6 and it will scratch a window glass. Apatite (left) has a hardness of 5 and can be scratched by a steel knife blade. Feldspar has a hardness of 6 and it will scratch a window glass.

Topaz has a hardness of 8 and will scratch quartz. Quartz (left), with a hardness of 7, is the hardest of the common minerals. It easily scratches hard glass and steel. Topaz has a hardness of 8 and will scratch quartz.

Corundum (left) has a hardness of 9. Corundum will scratch topaz. Diamond with its hardness of 10 can easily scratch the rest of the minerals.

Hardness finder! Find a mineral that is softer than calcite. Find a mineral that would scratch quartz. Find a mineral that fluorite would scratch.

On your own Create two questions using the hardness scale.

5. 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!

5. 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.

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

Cleavage or Fracture? Cleavage Halite

Cleavage or Fracture? Fracture Quartz

Cleavage or Fracture? Cleavage Biotite Mica

Cleavage or Fracture? Fracture Olivine

6. Reaction to Acid Calcite is calcium carbonate, CaCO3. If a drop of weak hydrochloric acid is placed on calcite, the acid bubbles as carbon dioxide is released.

7. Other special properties Magnetic Malleable Radioactive Flourescence Taste

Turn and talk: Looking at the samples below and what you’ve learned about minerals today what properties do you think you would use to identify them?