Minerals

6.E.2.3 Explain how the formation of soil is related to the parent rock type and the environment in which it develops.

Properties of Minerals

• What is a mineral?– Naturally occurring– Inorganic– Solid– Crystal structure– Definite chemical composition

Where are minerals found?

Naturally Occurring

• A naturally occurring substance is one that occurs in the natural world

• Materials made by people are NOT minerals

• Would a cubic zirconia be considered a mineral?

Inorganic

• Minerals cannot form from materials that were once part of living things

• For example: Coal– What is coal formed from?– Is it considered a mineral?– Would a bone be considered a mineral?

Solid

• Minerals are solids• What are the particles of a solid like compared to

those of a liquid or gas?

• A solid has a definite volume and shape

Crystal Structure

• Minerals have a crystal structure• Crystals have flat sides, called faces, that

meet at sharp edges and corners• The particles of minerals line up in a

pattern that repeats over and over again• How does this repeating pattern affect the shape of

the mineral?

Crystal Structure

Crystal Structure

Definite Chemical Composition

• A mineral always contains certain elements in definite proportions

• Almost all minerals are compounds• What is a compound?

• Some minerals occur in their pure form– Copper, silver, gold

• These minerals would also be considered what?

Chemical Composition

Identifying Minerals

• Geologists have identified about 3,800 minerals

• Each mineral has characteristic properties that can be observed simply by looking at the sample

• Other properties must be tested

Identifying Minerals

• Color• An easily observed characteristic• Color alone is often too little information to identify

a mineral

Identifying Minerals

• Streak• The color of a mineral’s powder• Streak and color are often different• Streak test= rubbing a mineral on an unglazed

ceramic tile

Identifying Minerals

• Luster• Term used to describe how light is reflected from a

mineral’s surface– Metallic, glass, waxy, greasy, pearly, submetallic or dull,

silky, and earthy

Metallic Glassy Earthy

Identifying Minerals

• Density• Each mineral has a characteristic density• Density is the mass in a given space

– Mass per unit volume

Identifying Minerals

• Hardness• Determined using Moh’s Hardness Scale

• Determined by scratch test

Identifying Minerals

• Crystal Systems• Crystals of each mineral grows atom by atom to

form that mineral’s particular crystal structure• Geologists classify these structures into six groups• Sometimes the crystal structure is obvious from

the mineral’s appearance• Sometimes the crystal structure is only visible

under a microscope• A few minerals are still considered minerals even

though their particles are not arranged in a crystal structure

Identifying Minerals

• Cleavage• A mineral that splits easily along a flat surface is

said to have cleavage

Identifying Minerals

• Fracture• Most minerals do not split evenly• Minerals that break apart in an irregular way are

described in terms of fracture– Types of Fracture:

• Curved, shell-like surface, hackly fracture – rough, irregular surfaces

Identifying Minerals

• Special Properties• Fluorescence, reactivity, magnetism, optical, and

electrical

How Minerals Form

• What is a geode?– A geode is a rounded, hollow rock that is

often lined with mineral crystals.

How Minerals Form

• How does a geode form?– Crystals form inside a geode when water

containing dissolved minerals seeps into a crack or hollow in a rock. Slowly, crystallization occurs.

How Minerals Form

• What is crystallization?– Crystallization is the process by which

atoms are arranged to form a material with a crystal structure.

How Minerals Form

• Two ways minerals can form:– Crystallization of magma and lava– Crystallization of materials dissolved in

water

How Minerals Form

• Minerals from magma and lava– Minerals form as hot magma cools inside

the crust, or as lava hardens on the surface. When these liquids cool to a solid state, they form crystals.

How Minerals Form

• Size – the size of the crystals depends on several factors:– the rate at which the magma cools– the amount of gas the magma contains– and the chemical composition of the

magma.

How Minerals Form

• Size of Crystals:– Rate of cooling:

• magma that cools below the surface cools slowly over many thousands of years

• Slow cooling leads to the formation of large crystals.

How Minerals Form

• Size of Crystals:– Rate of cooling:

• Magma closer to the surface cools much faster– rapid cooling does not provide enough time for

crystals to grow large– If magma erupts to the surface and becomes lava it

will cool quickly and form small crystals.

How Minerals Form

• Size of Crystals:– Undisturbed: if the crystals remain

undisturbed while cooling they grow by adding atoms according to a regular pattern.

How Minerals Form

• Minerals from Solutions:– Sometimes the elements and compounds

that form minerals can be dissolved in water to form a solution.• Solution: a mixture in which one substance is

dissolved in another.• Solute:

How Minerals Form

• Minerals from Solutions:– When elements and compounds that are

dissolved in water leave a solution, crystallization occurs.

How Minerals Form

• Minerals formed by Evaporation:– as water evaporates from a solution,

crystals form (halite, gypsum, calcite)

How Minerals Form

• Minerals from Hot Water Solutions:– When magma heats water deep under

ground, sometimes elements and compounds that form a mineral are dissolved in it. As the water cools, the elements and compounds leave the solution and crystallize as minerals.

How Minerals Form

• Vein:– pure metals that crystallize from hot water

solutions underground often form veins, or narrow channels or slabs of a mineral that is often different from the surrounding rock. The solutions of hot water and metals often flow through cracks within rocks, allowing the metal to crystallize into a vein.

Questions:

Because minerals do not come from once—

living material, they are said to be

A. crystalline.

B. solid.

C. colorful.

D. inorganic.

In a mineral, the particles line up in a repeating pattern to form a(n)

A. element.

B. crystal.

C. mixture.

D. compound.

Which characteristic is used to determine the color of a mineral’s powder?

A. luster

B. fracture

C. cleavage

D. streak

Which is true of all minerals?

A. They are inorganic solids.

B. They have a hardness of 4 or greater.

C. They have a glassy luster.

D. They can scratch a penny.

The End