Chapter 2Chapter 2MineralsMinerals

Section 2.1Section 2.1MatterMatter

• Standard 3c students know how to explain the properties of rocks based on the physical and chemical conditions in which they formed, including plate tectonic processes.

• Matter is anything that has volume and mass.

• Matter usually exists in one of three states– Solid which has definite shape and volume– Liquid has definite volume but not a definite

shape.– Gas neither has a definite volume or shape.

• Earth has nearly 4000 minerals each being unique.

• The building blocks for these minerals are elements.

Elements and the Periodic TableElements and the Periodic Table

• An element is a substance that cannot be broken down into simpler substances by chemical or physical means.

• There are more than 112 known elements, new elements are continuously being discovered.

• Of the 112 element 92 occur in nature while the remaining are made in laboratories.

• Elements are arranged on the Periodic Table. Each element is give a symbol made up of 1, 2, or 3 letters.

• Each element is known by its atomic number placed above the symbol.

• Most elements are not stable enough to exist in pure form in nature, and so most minerals are combinations of elements.

• The rows of the periodic table are called periods.

• The number of elements in a period varies.

• The columns in the periodic table are called groups. There are 18 groups on the periodic table

• Elements within a group have similar properties.

• Only 8 elements make up the Earth’s continental crust, 6 of which are classified as metals.

• Metals have specific properties that allow them to be drawn into wire and conduct heat and electricity. They also, form compounds.

AtomsAtoms

• All elements are made of atoms

• An atom is the smallest particle of matter that contains the characteristics of an element.

• The central region of an atom is called the nucleus and it contains protons and neutrons.

• Protons have a positive electrical charge

• Neutrons have no charge (neutral)

• Electrons are small particles with little mass and have a negative electrical charge. They surround the nucleus.

Protons and NeutronsProtons and Neutrons

• A proton has about the same mass as a neutron.

• The number of protons in the nucleus of an atom is called the atomic number.– Ex. All atoms with 6 protons are carbon atoms

and so the atomic # for carbon is 6.

• Atoms have the same number of protons and electrons– Ex. Carbon has 6 protons and 6 electrons

ElectronsElectrons

• An electron is the smallest of the three particles of an atom.

• An electron has a mass of about 1/1836 the mass of a proton or a neutron.

• Electrons move about the nucleus so rapidly that they create a sphere-shaped negative zone.

• Electrons are located in regions called energy levels

• Each energy level contains a certain number of electrons

• Q) How are electrons, protons, and neutrons alike and how are they different?

• A) They all are subatomic particles that make up atoms. Protons have positive electrical changes, neutrons have no charge, and electrons have negative charge. Protons and neutrons are found in an atom’s nucleus. Electron’s move about the nucleus.

IsotopesIsotopes

• Atoms of the same element always have the same number of protons, but the number of neutrons for atoms of the same element can vary.

• Atoms with the same number of protons but different numbers of neutrons are isotopes of an element.

• Isotopes of the same element are labeled using a convention call the mass number and with element’s name or symbol.

• The mass number of an atom is the total mass of the atom (protons plus neutrons) expressed in atomic mass unit.

• Carbon has 15 different isotopes.

• The nuclei of most atoms are stable, however, many elements have atoms whose nuclei are unstable.

• Such atoms disintegrate through a process called radioactive decay. This occurs because the forces that hold the nucleus together are not strong enough.

• During radioactive decay, unstable atoms radiate energy and particles. Some of this energy powers the movements on Earth’s crust and upper mantle.

• The rates at which unstable atoms decay are measurable and so radioactive atoms can determine the ages of fossils, rocks and minerals.

• Q) What are isotopes?

• A) atoms of the same element with the same # of protons, but diff # of neutrons.

Why Atoms BondWhy Atoms Bond

• Most elements exist combined with other elements to form substances with properties that are often different from the elements themselves. – Ex. sodium combines with chlorine to form the

mineral halite.

• Chemical combinations of the atoms of elements are called compounds

• A compound is a substance that consists of two or more elements that are chemically combined in specific proportions.

• Compounds form when the atoms are stable through a process called bonding.

• When atoms combine with others to form compounds, they gain, lose, or share electrons.

• Electrons move around the nucleus of an atom in a region called an electron cloud.

• Within the cloud, only a certain number of electrons can occupy each energy level. – Ex. Only 2 electrons can be in the 1st level. 8

electrons is the max. # for the 2nd level.

• When an atom’s outermost energy level does not contain the maximum number of electrons, the atom is likely to form a chemical bond with one or more other atoms.

• Chemical bonds can be thought of as the forces that hold atoms together in a compound

Types of Chemical BondsTypes of Chemical Bonds

• The main types of chemical bonds are ionic bonds, covalent bonds, or metallic bonds.

• Ionic bonds– An atom that gains electrons becomes

negatively charged because it has more electrons than protons.

– An atom that loses an electron is positively charged because it has more protons than electrons

• When an atom gains or loses one or more electrons is called an ion.

• Oppositely charged ions attract each other to form crystalline compounds

• Ionic bonds form between positive and negative ions.

• The properties of a compound are different from the properties of the elements in the compound.– Ex. Sodium is soft silvery metal that react with

water and will burn your skin. Chlorine is a poisonous gas, but as a compound they make table salt.

• Q) What happens when two or more atoms react?

• Compounds that contain ionic bonds are called ionic compounds.

• Ionic compounds are rigid solids with high melting and boiling points.

• In the solid state they are poor electrical conductors, but when melted many are good electrical conductors

• Q) How do ionic bonds form, and what are some properties of ionic compounds.

Covalent BondsCovalent Bonds

• Covalent bonds form when atoms share electrons.

• Compounds with these bonds are called covalent compounds.– Ex. Silicon dioxide. One silicon atom and two

oxygen atoms share electrons in their outermost energy level. Silicon dioxide is known as the mineral quartz.

• Covalent compounds have low melting and boiling points and are poor electrical conductor both in the solid and melted state.

• The smallest part of the covalent compound is a molecule, which is a neutral group of atoms joined by one or more covalent bonds. – Ex. Water consists of molecules. These

molecules are made up of 2 hydrogen atoms covalently-bonded to 1 oxygen atom.

Metallic BondsMetallic Bonds

• Metals are malleable, which means that they can be easily shaped. They are also excellent conductors of electricity.

• Metallic bonds form when electrons are shared by metal ions.

• The sharing of an electron pool gives metals their characteristic properties.

Section 2.1 AssessmentSection 2.1 Assessment

• 1. What is an element?

• 2. What kinds of particles make up atoms?

• 3. What are isotopes?

• 4. What are compounds and why do they form?

• 5. Contrast ionic, covalent, and metallic bonds.

Section 2.2 Section 2.2 MineralsMinerals

• Practically every manufactured product that you might use in a typical day contains materials obtained from minerals. – Ex. The desks and chairs, pencils, makeup,

windows

• Can you think of any others?

MineralsMinerals

• A mineral in Earth science is different from the minerals in foods.

• A mineral is a naturally occurring, inorganic solid with an orderly crystalline structure and a definite chemical composition.

• For an Earth material to be considered a mineral, it must have the following characteristics:– 1. Naturally occurring- forms from a

natural geologic process.

– 2. Solid substance- Solid within the normal temp. ranges on the surface of Earth

– 3. Orderly crystalline structure- atoms or ions are arranged in an orderly and repetitive manner.

– 4. Definite chemical composition- either a compound or a single element like gold and silver.

– 5. Generally considered inorganic- Most minerals are inorganic crystalline solids found in nature. Ex. Table salt.

How Minerals FormHow Minerals Form

• Minerals form nearly everywhere on Earth under different conditions. – Ex. Silicates form deep in the crust or mantle,

carbonates form in warm, shallow ocean waters,

• There are four major processes by which minerals form: crystallization from magma, precipitation, changes in pressure and temperature, and formation from hydrothermal solutions.

• Crystallization from Magma– Magma is molten rock that forms deep within

Earth. As magma cools elements combine to form minerals. The first minerals to crystallize are those rich in iron, calcium, and magnesium. As minerals continue to form the composition of the magma changes.

• Precipitation– The Earth’s lakes, rivers, ponds, oceans, and

beneath it’s surface contain many dissolved substances. Temperature changes and evaporation cause minerals to precipitate out.

• Ex. Limestone caves, halite and calcite.

• Pressure and Temperature– Some minerals form when subjected to

changes in pressure and temperature. An increase in pressure can cause a mineral to recrystallize while still solid; the atoms rearrange to form more compact minerals.

• Hydrothermal Solutions– A very hot mixture of water and dissolved

substances (100C and 300C). When the mixture comes in contact with minerals a chemical reaction takes place. When the solution cools element combine to form minerals like quartz and pyrite.

Mineral GroupsMineral Groups

• Over 3800 minerals have been named, with several new ones being identified each year.

• Common minerals, together with the thousands of others that form on Earth, can be classified into groups based on their composition.

• Common mineral groups: silicates, carbonates, oxides, sulfates, sulfides, halides and native elements.

• Silicates– Silicon and oxygen are the two most abundant

elements on Earth– Silicon and oxygen combine to form a

structured called the silicon-oxygen tetrahedron

– The tetrahedron, which consists of one silicon atom and four oxygen atoms, provides the framework of every silicate mineral.

– The silicon-oxygen bonds are very strong.– Augite forms single chains, hornblende forms

double chains, micas form sheets, quartz forms three-dimensional network structures.

• Q) What is the silicon-oxygen tetrahedron?

• A) It consists of one silicon atom and four oxygen atoms and provides the framework of every silicate mineral.

Silicate cont’d………………….Silicate cont’d………………….– The formation of silicates can occur at great

depths, where temperature and pressure are high. The place of formation and chemical composition of the magma determines which silicate mineral will form

• Ex. Olivine crystallizes at 1200C and Quartz crystallizes at 700C.

– Some minerals form on Earth’s surface when exposed to weathering

• Ex Clay minerals form this way.

• Carbonates–The second most common mineral

group.– Carbonates are minerals that

contain the elements carbon, oxygen, and one or more other metallic elements.• Ex. Calcite is the most common.• Dolomite contains magnesium.• Limestone and marble are rocks used in building and construction

• Oxides– Oxides are minerals that contain oxygen and

one or more other elements, which are usually metals.

– Rutile forms as magma cools deep beneath Earth’s surface. Rutile is titanium oxide

– Corudum form when existing minerals are subjected to changes in temperature and pressure. This is also know as aluminum oxide.

– Hematite forms when exposed to liquid water or to moisture in the air. Known as iron oxide

• Sulfates and Sulfides– Sulfates and sulfides are minerals that

contain the element sulfur.

– Sulfates Anhydrite and gypsum form when mineral-rich water evaporate.

– Sulfides galena, sphalerite, and pyrite form from thermal, or hot-water solutions.

• Halides–Halides are minerals that contain a

halogen ion plus one or more other elements.

–Halogens are elements from Group 7A on the periodic table. Includes: fluorine and chlorine

–The mineral halite (table salt) is a common halide.

–Fluorite forms when salt evaporates water and is used in making steel.

• Native Elements– Native elements are a group of minerals

that exist in relatively pure form.• Gold, silver, copper, sulfur, and carbon

– Native forms of carbon are diamonds and graphite.

Section 2.2 AssessmentSection 2.2 Assessment

• 1. What are 5 characteristics of a mineral?

• 2. Describe 4 processes that result in the formation of minerals.

• 3. How can minerals be classified?

• 4. Name the major groups of minerals, and give at least 2 examples of minerals in each groups.

Section 2.3Section 2.3Properties of MineralsProperties of Minerals

• Minerals occur in different colors and shapes the vary in the way they reflect light and in the way they break. Some are harder than others and some smell like rotten eggs. All these properties can be used to identify them.

ColorColor

• Color is often not the best way to identify many minerals

• Small amounts of different elements can give the same mineral different colors.

StreakStreak

• Streak is the color of mineral in its powdered form.

• Streak is obtained by rubbing a mineral across a streak plate, a piece of unglazed porcelain. Even though the color may vary from sample to sample the streak will always be the same.

• Show the difference between metallic and nonmetallic luster.

LusterLuster• Luster is used to describe how light is

reflected from the surface of a mineral.• Minerals that have the appearance of

metal regardless of color are said to have luster.

• Described as vitreous, glassy, pearly, silky, and earthy, adamantine, or brilliant luster.

• Some mineral appear somewhat metallic and are said to have sub-metallic luster

Crystal FormCrystal Form

• Crystal form is the visible expression of a mineral’s internal arrangement of atoms.

• Every mineral has a distinct crystal form.• When a mineral forms slowly and without

space restrictions, it will develop into a crystal with well-formed faces, sides, top and bottom.

• When minerals compete for space the result is an intergrown mass of small crystals.

HardnessHardness

• Hardness is one of the most useful properties to identify minerals.

• Hardness is a measure of the resistance of a mineral to being scratched.

• Geologist use a standard hardness scale called the Mohs scale.

• The Mohs scale consists of 10 minerals arranged from 10 (hardest) to 1 (softest)

• Any mineral of unknown hardness can be rubbed against these to determine its hardness.

• Your fingernail has a hardness of 2.5 and will scratch gypsum, but not calcite.

• Quartz is the hardest of the most common minerals with a hardness of 7.

• Diamonds are the hardest mineral on Earth and can scratch anything.

• Q) Describe 3 or 4 of the most useful properties for identifying unknown minerals.

CleavageCleavage

• Cleavage is the tendency of a mineral to cleave, or break, along flat, even surfaces.

• Micas show the simplest type of cleavage because they have weak bonds within their atomic structure in on direction, they cleave to form thin, flat sheets.

• Some minerals have cleavage in more than one direction.

FractureFracture

• Minerals that do not show cleavage when broken are said to fracture.

• Fracture is the uneven breakage of a mineral.

• Minerals that break into smooth, curved surfaces have a conchoidal fracture like quartz.

• Asbestos breaks into splinter or fibers.• Many minerals have an irregular fracture.

DensityDensity

• Density is a property of all matter that is the ration of an object’s mass to its volume. Density=Mass/Volume

• Common minerals have a density between 2 and 5 g/cm3.

• Density can be used to determine the purity or identity of some minerals

Distinctive Properties of MineralsDistinctive Properties of Minerals

• Some minerals can be recognized by other distinctive properties.

• Talc feels soapy, graphite feels greasy.

• Metallic minerals are easily shaped.

• Magnetite will attract paper clips.

• A mineral’s properties depend on the elements that compose the mineral and its structure.

Section 2.3 AssessmentSection 2.3 Assessment

• 1. Describe 5 common properties of minerals that can be used to identify them.

• 2. How is the Mohs scale used?• 3. What are some unique properties that

can be used to identify minerals?• 4. How are cleavage and fracture

different?• 5. What 2 conditions produce crystals with

well-defined faces?