CH. 5 MINERALS

Loulousis

Objectives 5.1

Define the term mineral

Identify the 2 ways that minerals form

Compare the two main groups of minerals

Mineral Song

http://www.youtube.com/watch?v=-F0IA21bgmM

An Introduction

Mineralogy- study of minerals, subdivision of geology

96% of Earth’s crust is composed of minerals

Atoms make up minerals, minerals make up rocks

How Minerals Form

Crystallization: process of mineral formation, atoms are arranged to form material with crystal structure

1. Solidification of a melt

Magma or lava cools and hardens

How most rocks form

2. Precipitation from solution

Liquids cool to solid state

Precipitation from solution

Example: Salt water

Contains electrically charged atoms (ions)

When salt water evaporates the water becomes saltier, because the ions left behind which are attracted to each other and begin to link together and form mineral crystals

Any natural water will precipitate some minerals through evaporation

Mineral Characteristics Mineral: a natural, inorganic solid that has a

characteristic chemical composition, an orderly internal structure, and a characteristic set of physical properties.

To be a mineral, a substance must have four characteristics:

it must be inorganic—it cannot be made of or by living things;

it must occur naturally—it cannot be man-made; it must be a crystalline solid; it must have a consistent chemical composition.

1. Inorganic

Inorganic- when substance is not made of living things or the remains of living things

Minerals are not organic compounds unlike amino acids, peptides or enzymes are

Oddly, many organic processes result in the formation of minerals ex) teeth and bones

2. Naturally Occurring

Found and created in nature

Products of industrial or commercial processes are not true minerals

3. Solid crystalline structures

Crystalline means that atoms within the solid are arranged in a geometric pattern

The pattern is unique to each mineral

If pattern is altered, it creates a new mineral

Ice is a mineral, while liquid water and steam is not

4. Chemical composition

All minerals have a chemical composition

Means there is a chemical formula for each mineral ex) NaCl

There are some impurities in minerals which means an element may slip into a crystalline structure that should not be there

Four Characteristics of Minerals

Mineral yes or no ? http://www.oum.ox.ac.uk/thezone/minerals/define/quiz/

Kinds of Minerals

More than 3,000 kinds of minerals, but only about 20 are common

Common minerals are rock-forming minerals

10 common minerals make up 90% of the mass of Earth’s crust

Quarts, orthoclase, plagioclase, muscocvite, biotite, calcite, dolomite, halite, gypsum, and ferromagnesian

1. Silicate Minerals

Mineral that contains a combination of silicon and oxygen

Can have one or more metals in addition to silicate and oxygen

Feldspars are the most common

Silicate minerals make up 96% of the Earth’s crust

2. Nonsilicate Minerals

Mineral that does not contain compounds of silicon and oxygen

About 4% of Earth’s crust

6 major : carbonates, halides, native elements, oxides, sulfates, sulfides

Exit Slip

1. What are the two ways minerals form?

2. What are the 4 characteristics of a mineral?

3. What are silicate minerals?

4. What are non-silicate minerals?

Objectives

Identify and describe the 6 types of silicate crystalline structures

Describe three common nonsilicate crystalline structures

Crystalline Structure

Each type of mineral is characterized by a specific geometric arrangement of atoms

Crystal: a solid whose atoms, ions, or molecules are arranged in a regular repeating pattern.

Scientists determine the structure of crystal by using X rays

There are 6 basic crystal shapes

Crystalline Structure of Silicate Minerals Silicate minerals all have the same basic

building blocks of silicon-oxygen tetrahedra that forms its crystalline structure

silicon-oxygen tetrahedron : basic unit of the structure of silicate minerals; a silicon ion chemically bonded to and surrounded by four oxygen ions

* you should be familiar with images of all the silicate mineral structures! Pg. 107

1. Isolated Tetrahedral

Do not link with other silicon or oxygen atoms

Only atoms other than silicon and oxygen atoms link with the silicon-oxygen tetrahedra

Example: olivine, oxygen from tetrahedra links with Mg or Fe atoms

2. Ring silicates

Form rings by sharing oxygen atoms

Can form three, four, or six sided rings that align to make channels for ions or molecules

Ionic bonds hold the rings together

Example: Beryl and Tourmaline

3. Single-Chain Silicates

Form a chain by sharing oxygen atoms

Each tetrahedron is bonded to two others by shared oxygen atoms

Called pyroxenes

4. Double-Chain Silicates

Form when two single-chains of tetrahedra bond to each other

Called amphiboles

5. Sheet Silicates

Form when each tetrahedron shares three of its oxygen atoms with other tetrahedra

The fourth oxygen atom bonds with an atom of Al or Mg which connects the sheets together

Examples: muscovite and biotite

6. Framework silicates

Form when each tetrahedron is bonded to four other tetrahedra

Frameworks that contain only silicon-oxygen tetrahedra form the mineral quartz

Feldspars contain tetrahedra with Al or other metals in place of the silicon

Crystalline Structure of Nonsilicate Minerals Common crystal structures include cubes,

hexagonal prisms, and irregular masses Can form tetahedral similar to silicates but the

ions at the center are not silicon The structure of a nonsilicate crystal

determines the mineral’s characteristics.

In crystal structure called closest packing, each metal atom is surrounded by 8 to 12 other metal atoms that are as close to each other as the charges of the atomic nuclei allow.

Stop and Think

1. What compound of elements will you never find in a nonsilicate mineral?

2. What is the building block of the silicate crystalline structure?

Objectives

Describe the seven physical properties that help distinguish one mineral from another

List the 5 special properties that may help identify certain minerals

Identify minerals using their seven physical properties

5.2 Identifying Minerals

To identify minerals scientists called mineralogists examine and analyze the properties of minerals

Each mineral has specific properties that are a result of its chemical composition and crystalline structure

1. Color

color is a property that is easily observed, but by itself is unreliable for the identification of minerals.

The color of a mineral sample can be

affected by the inclusion of impurities or by weathering processes.

2. Streak

Streak: color of a mineral in powdered form

Observed by rubbing some of the mineral on an unglazed ceramic tile called a streak plate

Streak color can differ from the color of the solid mineral

Streak is more reliable than color for the identification of minerals

3. Luster

Luster: the way in which a mineral reflects light A mineral is said to have a metallic luster if the

mineral reflects light as a polished metal does.

All other minerals have nonmetallic luster.

There are several types of nonmetallic luster, including glassy, waxy, pearly, brilliant, and earthy.

Mini video

4. Hardness

Hardness: the measure of the ability of a mineral to resist scratching

Hardness does not mean “resistance to cleavage or fracture.”

The hardness of a mineral can be determined by comparing the mineral to minerals of Mohs hardness scale.

Mohs hardness scale: the standard scale against which the hardness of minerals is rated

The strength of the bonds between the atoms that make up a mineral’s internal structure determines the hardness of a mineral.

Mohs Hardness Scale

5. Cleavage and Fracture

Cleavage: in geology, the tendency of a mineral to split along specific planes of weakness to form smooth, flat surfaces

Fracture: the manner in which a mineral breaks along either curved or irregular surfaces

Uneven or irregular fractures have rough surfaces.

Splintery or fibrous fractures look like a piece of broken wood.

Curved surfaces are conchoidal fractures . Mini video

6. Crystal shape

6 basic chapes: isometric or cubic, tetragonal, monoclinic, orthorhombic, hexagonal, triclinic

A certain mineral always has the same general shape because the atoms that form the mineral’s crystals always combine in the same geometric pattern

Review table 2 on pg. 112

7. Density

Density: the ratio of the mass of a substance to the volume of a substance; commonly expressed as grams per cubic centimeter for solids

The density of a mineral depends on the kinds of atoms in the mineral and on how closely the atoms are packed.

density = mass volume

8.Special Property: Fluorescence and Phosphorescence

Fluorescence: The ability to glow under ultraviolet light

Fluorescent minerals absorb ultraviolet light and then produce visible light of various colors.

Phosphorescence: The property of some

minerals to glow after the ultraviolet light is turned off

9.Special Property: Chatoyancy and Asterism In reflected light, some minerals display a

silky appearance that is called chatoyancy, or the cat’s-eye effect.

A similar effect called asterism is the phenomenon in which a six-sided star appears when a mineral reflects light.

Double refraction: The property of some minerals to produce a double image of any object viewed through the mineral Example: calcite

Magnetism

Minerals that are attracted to magnets display the property of magnetism.

These minerals may be magnetic

themselves.

In general, nonsilicate minerals that contain iron are more likely to be magnetic than silicate minerals are.

Radioactivity

Radioactivity results as unstable nuclei

decay over time into stable nuclei by releasing particles and energy.

A Geiger counter is used to detect the released particles and, thus, to identify minerals that are radioactive.

Stop and Think

What determines the hardness of a mineral?

What is the difference between chatoyancy and asterism?

What is the two main types of luster?