CHAPTER 9: MINERALS OF THE EARTH’S CRUST

What is a mineral?A mineral:•is inorganic•is naturally occurring•is a crystalline solid•has a definite chemical c

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Inorganic?• Inorganic means that it is not made

by a living organism.

• Coal is made from the remains of plants.

• Coal is NOT a mineral because it is NOT inorganic.

to “What is a Mineral?”

Naturally Occurring?• Steel and brass are compounds

made by humans.

• Steel and brass are not found in nature

• Steel and brass are NOT naturally occurring and so they are NOT minerals.

to “What is a Mineral?”

A Crystalline Solid?• A solid is the physical form of matter with

a definite shape and volume.

• Crystalline means the atoms are arranged in a regular and repeating pattern:

Definite Chemical Composition?

• Calcite consists of calcium, carbon, and oxygen in definite amounts. Calcite is a mineral

• Concrete consists of cement, gravel, sand, and water. The amounts of each can vary depending on what you are using the concrete for. Concrete is not a mineral

to “What is a Mineral?”

The Two Main Mineral Groups1. Silicates:Minerals that contain silica (silicon [Si]

and oxygen [O] combined), and usually some other element(s). Silicate minerals make up 96% of the earth’s crust. Most common are Feldspars.

2. Nonsilicates:Minerals that do not contain silica.

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Most Common Elementsmagnesium (Mg)

potassium (K)

iron (Fe)

sodium (Na)

calcium (Ca)

oxygen (O)silicon (Si)aluminum (Al)

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Six Nonsilicate Groups1. Carbonates • Contain CO3 (carbonate group)• Examples calcite, dolomite

2. Halides• Contain a halide element (Group VIIA on the Periodic Table)• Examples halite, fluorite

3. Native Elements• Elements uncombined with other elements• Examples sulfur

4. Oxides• Contain oxygen and an element other than silicon• Examples hematite

5. Sulfates• Contain SO4 (sulfate group)• Example gypsum

6. Sulfides• Contain sulfur and another element• Examples galena, pyrite to

9.1

Characteristics of MineralsColorLusterStreak

Cleavage/FractureHardness

Crystal ShapeDensity

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Color?Easiest property to see, but seldom usefulMany minerals are the same color

Some minerals come in several colors

calcite

quartz

talc

feldspar

calcite quartz

Color?For a few minerals, color is a very good property for

identification! Here are some examples:

• pyrite

• sulfur

• galena

to “Characteristics”

Luster?• Definition: light

reflected from the surface of a mineral

• Two main types:1. metallic—looks like

polished metal

2. nonmetallic—does not look like polished metal!

to “Characteristics”

Streak?• Definition: color of a mineral

in powdered form

• Rub the mineral on a piece of unglazed ceramic tile (called a streak plate)

• Most metallic minerals have dark streak

• Most nonmetallic minerals have white or light-colored streak

to “Characteristics”

Cleavage?• Definition:

splitting of a mineral along smooth, flat surfaces

• Cleavage surfaces form where atomic bonds are weak

to “Characteristics”

Fracture?• Definition: breakage along irregular

surfaces (absence of cleavage)

quartzto “Characteristics”

Hardness?• Definition: ability of a mineral to

resist scratching

Softest

Hardest

What is the hardness of a mineral that can scratch feldspar but not quartz?

6.5

to “Characteristics”

Crystal Shape?• Definition: the form taken by a mineral as a

result of its internal arrangement of atoms

• Flat surfaces on crystals are called “crystal faces.”

• Most crystals don’t show crystal faces because they don’t have enough room to form.

to “Characteristics”

amphibole crystals

crystal faces on all sides no crystal faces

Density?• Definition: the amount of matter in a given

volume of a substance (formula is: density = mass/volume, or D = m/v)

• When you have two objects the same size, the one that “feels heavier” has higher density, the one that “feels lighter” has lower density.

• Go to Gizmo

to “Characteristics”

Special Properties of Minerals

• Magnetism

• Fluorescence and phosphorescence

• Double refraction

• Radioactivity

• Reaction to hydrochloric acid

to 9.2

Magnetism?• Most common magnetic mineral is:

magnetite

to Special Props

• Sometimes magnetic: pyrite (fool’s gold)

Fluorescence/Phosphorescence?• Fluorescence

glows under ultraviolet light

• Phosphorescenceglows after ultraviolet light is turned off

to Special Props

Double Refraction?

• Transparent minerals that can split a light ray into two parts (ex: calcite)

to Special Props

Radioactivity• The breakdown of a nucleus because it

is unstable• Caused by arrangement and number of

protons and neutrons in the nucleus

to Special Props

uraninite

uranium oxide

processed uranium ore

Mineral Resources• Steel is made from iron and iron rich minerals

(cars, building material) • Quartz (sand) used for making glass• Alloys of magnesium and aluminum• Titanium and molybdenum (aircraft and bicycles)• Gemstones (diamonds for jewelry and cutting and

grinding tools)• Graphite (pencils, paint,lubricants and batteries) • Galena (lead) used in car batteries; in solder

Mineral Identification • Mineral Identification Activity