EARTH/SPACE SYSTEMS

EARTH MATERIALS AND PROCESSES UNIT

MINERALS SUB-UNIT

Minerals: Physical Properties

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 an orderly pattern.

5. A mineral is inorganic (was never alive)

Of the almost 4000 known minerals, only about 30 are common.

The most common are quartz,feldspar,mica, and calcite.

These minerals make up most of the rocks found in the

Earth’s crust.

How do geologists classify minerals?

Identified about 3,800 mineralsEach has characteristic properties that can

be used to identify itWhat do you predict some of those

characteristic properties might include?

Video clip on Rocks and Minerals

Why do we “care” about minerals? How do they impact our daily lives?http://www.youtube.com/watch?v=9cHUbyaid

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COLOR

Easily observed physical propertyOften too little information to make identificationCan only be used to identify minerals that always

have own characteristic color

Examples: - Gold, Pyrite, and Chalcopyrite all have gold color,

so you need additional information to identify these minerals

- Malachite is always green

Action! Arrange your minerals by color

How did your group arrange the minerals?Was arranging them by color easy or

difficult?What considerations did you need to make?Were there any minerals that you found

difficult to place by color? Why?

Streak of a mineral is the color of its powder when rubbed on

an unglazed white tile.

The streak is often not the same color as the mineral.

A minerals color may vary, but the streak rarely will!

STREAK

To do this test, rub the mineral across a piece of unglazed porcelain tile and see what color the powder is

Examples:- Pyrite has a gold color but a greenish black

streak- Gold has a gold color and a golden yellow

streak

Action! Streak Test

Use the unglazed tile and try the streak test on your minerals.

Which mineral left a streak that was the same color as your mineral?

Which mineral left a streak that was a different color than the mineral?

Was there anything about running this test that your group had difficulty doing?

Luster refers to the way a mineral shines in reflected light.Notice the difference between

these two minerals?

The mineral on the left has a metallic luster, the one on

the right, a nonmetallic luster.

There are several terms used to describe nonmetallic luster.

Examples could be vitreous, like the quartz on the left, or pearly,

like the gypsum on the right.

Other terms that might be used include greasy, dull, and earthy.

Can you tell which of these has an earthy luster and which has a

vitreous luster?

Earthy

Vitreous

LUSTER

Examples:- Galena is an ore of lead, and has a bright,

metallic luster- Quartz has a glassy luster

Action! Identify the luster of your minerals.

Look on page 117 (red) or 123 (orange) in Inside Earth textbook.

Identify the luster for each of your minerals.- How did your group classify mineral 1?- How did your group classify mineral 2?- How did your group classify mineral 3?- How did your group classify mineral 4?- How did your group classify mineral 5?Did your group have trouble identifying the

luster for any of these minerals?

DENSITY

Each mineral has a characteristic density.Density is the mass in a given space, or mass

per unit volume.You can “heft” or feel a mineral’ weight by

picking two mineral samples up and comparing their weight.

How do you think geologists could precisely measure the mass of a mineral sample?

Measuring Density

Geologists measure density by using a balance to determine the mineral sample’s mass, and then by placing the mineral in water and determining how much water was displaced.

The volume of water displaced equals the volume of the sample.

Dividing the sample’s mass by its volume gives the density of the mineral.

Density = mass/ volume

Density Problem

If a sample of Olivine has a mass 237 grams and a volume of 72 ml (cm3), then the density will be

- 237 g/ 72 cm3 = 3.3 g/cm3

Now your turn! A sample of Calcite has a mass of 324 grams and a volume of 120 ml (cm3).

What is its density?

320 grams / 120 cm3 = 2.7 g/ cm3

HARDNESS

One of the best clues when identifying mineralsIn 1812, Friedrich Mohs developed the “Mohs

hardess scale” to describe the hardness of mineralsRanks ten minerals from softest to hardestCan be determined by a “scratch test”A mineral can scratch any mineral softer than itself,

and can be scratched by a mineral that is harder.Which of these minerals do you think is the softest? Quartz, Diamond, or Talc

Mohs Hardness Scale

Talc = 1

The softest know mineralTalc flakes when scratched by a fingernailUsed as a powder on people’s skin

Gypsum = 2

A fingernail can easily scratch it!Used in plaster, shampoo, hair products, and

foot creams

Calcite = 3

A fingernail can’t scratch it, but a penny can!One of the most common elements on EarthPrimary mineral in cave formationsAlso most sea shells are composed of calcitePulls carbon dioxide out of sea and thus

functions as a filter for EarthWill fix and dissolve when in an acidic solutionUsed in construction: limestone, marbleAlso in paint, animal feed, and as a cleaner

Fluorite = 4

A steel knife can easily scratch this mineral.Is used in aluminum, on dishes that can go in

the oven, in telescopes and lenses, and for ornamental uses

Apatite = 5

A steel knife can scratch this mineral as well, though not as easily as Fluorite.

Used commonly in fertilizers

Feldspar = 6

It can’t be scratched by a steel knife, but it can scratch window glass.

Used in ceramics and cleanersMost abundant mineral found in Earth’s crust

Quartz = 7

It can easily scratch steel and hard glass.Second most abundant mineral found in

Earth’s continental crustmaking of sandpaper, optics, glass, circuit

boards, computer components, cement , mortar, and jewelry.

Time can be measured from the vibrations of the quartz crystals so quartz crystals are often used in clocks.

Topaz = 8

It can scratch quartz.Most common use is as a gemstone in

jewelry.

Corundum = 9

Used as an abrasive

Diamond = 10

Mostly use as gemstones but also used in semiconductors, cutting, grinding, and drilling

Hardest mineral

Action! Run hardness tests on your minerals.

Use the penny and steel nail to arrange your minerals from softest to hardest.

Look on p. 122 (orange) or 118 and 119 (red) to determine where each mineral might fall on the Mohs hardness scale.

Where did you classify mineral 1?Where did you classify mineral 2Where did you classify mineral 3?Where did you classify mineral 4?Where did you classify mineral 5?

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.

Crystal Systems

- Crystals of each mineral grow atom by atom to form that mineral’s crystal structure

- Geologists classify minerals into six groups based on the number and angle of the crystal faces.

Look in Inside Earth on p. 124 (orange) or pp. 120 -121 (red).

What is the crystal system of quartz called? What is its density?

What is the crystal system of Magnetite? What is its density?

What is the crystal system of quartz called? Hexagonal

What is its density? 2.6 g/cm3

What is the crystal system of Magnetite? Cubic

What is its density? 5.2 g/cm3

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

This is determined by how the atoms in its crystal are arranged.

This arrangement causes the mineral to break apart more easily in one direction than in another.

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

Fracture

“Fracture” describes how a mineral looks when it is broken apart in an irregular way.

Geologists use many terms to describe this characteristic; including

- “shell-shaped” when it breaks and leaves a surface that looks like a seashell

- “hackly” when pure metals, such as copper and iron break, and form jagged points.

- “earthy” when soft minerals crumble like clay

Special Properties

Look at p. 126 (orange)and p. 122 (red) to find examples of each of these special properties-

Magnetism: has properties of magnets Magnetite or Lodestone

Fluorescence: glows under ultraviolet light Scheelite

Optical properties: bends light Calcite

Reactivity: reacts chemically Calcite, Aragonite

Special Properties Examples