aim: how can we describe a mineral?

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.

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?

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?

Water

Gold

Pearls

Mineral or Not?

Diamond Coal

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.

The most common are

quartz

feldspar

micacalcite

Minerals are arranged into groups…

• According to their chemical and physical properties.

Mineral Groups

•Silicates•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 MineralsWithout 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.

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!

ColorMany minerals have a similar

color.

ColorsMany 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?

• Metallic• Galena

Metallic or Non-metallic?

• Non-metallic• Quartz

Metallic or Non-metallic?

• 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.

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.

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.

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.

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.

5. Cleavage

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

Malleable

Magnetic

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?