Chapter 5 Section 1 What is a mineral?

Objectives 1.Define mineral. 2. Compare the two main groups of minerals. 3. Identify the six types of silicate crystalline structure. 4. Describe three common nonsilicate crystalline structures.

How do you determine if a substance is a mineral?

Classifying Minerals

Four basic questions:

Is the substance inorganic? Magnetite is inorganic and contains iron and oxygen. Coal is organic and is made from plants.

Is it naturally occurring? The mineral quartz occurs naturally in the earth. Steel and brass are man-made.

Is it a solid in crystalline form? Diamond has a solid crystalline structure. Petroleum and natural gas are naturally occurring but are not solids.

Does it have a definite chemical composition? The mineral fluorite is made of calcium and fluorine (CaF 2 ) Concrete is made up of several substances.

Minerals: must be inorganic must be naturally occurring must be a solid with an internal crystalline structure must have a definite chemical makeup.

There are over 3,000 known minerals Many may be easily identified, although lab tests are needed to be conclusive.

Elements in the Earth’s Crust

Even though there are 92 elements that are naturally found, only eight of them are common in the rocks that make up the Earth’s outer layer, the crust. Together, these 8 elements make up more than 98% of the crust.elementscrust The 8 most common elements in Earth’s crust (by mass): 46.6% Oxygen (O) 27.7% Silica (Si) 8.1% Aluminum (Al) 5.0% Iron (Fe) 3.6% Calcium (Ca) 2.8% Sodium (Na) 2.6% Potassium (K) 2.1% Magnesium (Mg) The picture on the left shows where these elements are located within the periodic table. Together, the elements oxygen and silicon make up most of the Earth’s crust including silicate minerals such as quartz and feldspar.periodic tablesilicate mineralsquartzfeldspar

Identifying Minerals Section 5.2

Objectives Describe seven physical properties that help distinguish one mineral from another. List 5 special properties that may help identify certain minerals

Physical properties of minerals are a result of the chemical composition and crystalline structure

Talc is highly variable, yet Sulfur is almost always yellowish. Talc  Sulfur Color Color : Can be very characteristic for a few minerals, but is not important for others Talc

Luster: the way light is reflected either Metallic or Non-metallic

Non-metallics are further described as: dull (earthy) waxy pearly (translucent) glassy (transparent)

Hematite has a very red streak Streak: the color of the powdered mineral

Cleavage and Fracture how a mineral splits or how a mineral breaks

Moh’s Hardness Scale

We use a scale from 1 to 10 called MOH’S SCALE OF HARDNESS. Talc is a 1 and diamond is a 10. Most minerals fall between 3-6. The field scale can be very helpful:

Field Scale of Hardness Finger Nail 2.5  Penny 3.5  Nail or Knife 5.0 to 5.5  Glass 5.5 to 6.0

Specific Gravity (heft): Density = Mass/Volume SG = Density of Sub./Density of H 2 O Dry weight of Mineral SG = Dry weight - weight in water

Example low and high Specific Gravity Graphite (low)  Galena (high)

Unique Characteristics of a few minerals

Magnetism: Some minerals are attracted to a magnet. Magnetite

Fluorescence: Minerals which will glow under an ultraviolet (black) light. Minerals that continue to glow after the ultraviolet light is cut off are called phosphorescent. Opal

Chatoyancy and Asterism Chatoyancy: Silky appearance due to large numbers of parallel mineral fibers. Asterism: Six-sided star shape when the mineral reflects light.

Radioactivity: Some radioactive minerals will emit charged particles that are detected by a geiger counter. Uranitite

Malleability: Some minerals are bendable  Some minerals are brittle GarnetCopper

Feel: Some minerals feel greasy or soapy (unctuous) Graphite

Solubility: Some minerals are soluble (will dissolve) in water Halite

Double Refraction: Optical properties reveal a double image Iceland Spar (Calcite)

Taste: Some minerals taste salty. Halite

React with acids: Carbonates react with hydrochloric acid and give off CO 2 gas Calcite

Rocks: are solid materials that are made up of one or more minerals. Lets click here to find out more

Rock-forming minerals Of the 3,000 minerals, fewer than 20 form most of the earth’s crust.

Of these 20, only 10 are common, and these make up 90% of the earth’s crust

All minerals can be classified into two main groups based on their chemical composition. SilicatesNonsilicates

Silicate minerals contain atoms of silicon (Si) and oxygen (O) SiO 2

Silicate minerals make up 96% of the earth’s crust. Quartz Feldspar (orthoclase) Feldspar (plagioclase)

Silicates which are rich in iron and magnesium include: Hornblende Olivine Muscovite Biotite

Nonsilicate Minerals Make up only 4% of the earth’s crust Six Major Groups

Carbonates Compounds that contain a carbonate group (CO 3 )

Halides Compounds that consist of chlorine or fluorine combined with sodium, potassium or calcium

Native Elements Elements uncombined with other elements

Oxides Compounds that contain oxygen and an element other than silicon Hematite Fe 2 O 3

Sulfates Compounds that contain a sulfate group (SO 4 )

Sulfides Compounds that consist of one or more elements combined with sulfur

Crystalline Structure a natural solid with a definite shape The conditions under which minerals are produced do not usually allow large single crystals to grow.

Crystalline Structure of Silicate Minerals Silicon-oxygen tetrahedron Silicon atom bonded to four atoms of oxygen in a pyramid arrangement

Variations

Ionic Silicates Silicon-oxygen tetrahedra linked only by atoms of elements other than silicon and oxygen

Single and Double Chained Silicates

Single Chain Silicates In single-chain silicates each tetrahedron is bonded to two others by shared oxygen atoms Minerals made up of single chains are called pyroxenes

Double Chain Silicates In double-chain silicates, two single chains of tetrahedra bond to each other. Minerals made up of double chains are called amphiboles

Tetrahedral Sheets Each tetrahedron shares three oxygen atoms with other tetrahedra. The fourth oxygen atom bonds with an atom of K or Al, which joins one sheet to another.

Examples of Tetrahedral Sheets Muscovite Biotite

Network Silicates Each tetrahedron is bonded to four neighboring tetrahedra Network silicates tend to form very hard crystals.

Examples of Network Silicates Quartz Feldspar

Assignments Section 5.1 Outline Key Terms Direct Reading