The LithosphereUnit 9, Lesson 9.2

By Margielene D. Judan

Lesson Outline• The Lithosphere• Rocks• Igneous, Sedimentary and Metamorphic Rocks• Minerals• Properties of Minerals• The Soil

The Lithosphere• Solid portion of the earth• Lithosphere = crust + upper

mantle• Composed of rocks and minerals

Petrology• The science that deals with the study of the formation, composition, and classification of rocks.

Rocks• A solid aggregate (group) of:

1. Single mineral 2. Group of minerals

Classification of Rocks• Rocks differ in color• Color is determined by the type of mineral that composes the rock.

Classification of Rocks• Rocks differ in texture,

determined by the time it takes for them to crystallize.• Aphanitic – smooth

and very fine crystals• Phaneritic – rough

and large crystals• Porphyritic – large

and small crystals combined

Classification of Rocks• Igneous• Sedimentary•Metamorphic

Igneous Rocks• Formation: cooling

and solidification of magma or lava• Classified into 2 types:• Intrusive – cools very

slowly beneath the surface and is created by magma.• Extrusive – cools very

fast on the surface and is created by lava.

Lava vs. Magma•Magma – composed of molten rock and is stored in the Earth's crust• Lava – magma that reaches the surface of our planet through a volcano vent

Igneous RocksExamples: •Granite – main component of continental crust• Scoria – volcanic rock w/ many holes (forms whe gases escape and the magma solidifies)•Obsidian – appears as chunk of synthetic glass• Basalt – denser than granite; forms in ocean floor

Scoria

Sedimentary Rocks• Formation: small particles (sediments) that have been compacted and cemented together • Lithification – process of forming a sedimentary rock• Cementing materials – lime, iron oxide, silica• Result of weathering and erosion• Sediments – small particles of weathered rocks

Sedimentary Rocks• Sediments and their Sedimentary Rock Equivalent

Sediments Sedimentary RockSand Sandstone

Gravel ConglomerateClay, mud Shale

Shells and skeletons LimestonePeat (plant remains) Lignite (soft coal)

Metamorphic Rocks• Formation: extreme heat at pressure in the earth’s interior•Underwent chemical change•More crystalline, harder and denser• Igneous rock + heat + pressure = metamorphic rock• Sedimentary rock + heat + pressure = metamorphic rock

Metamorphic Rocks• Sedimentary Rock and Their Metamorphic Equivalent

Sedimentary Rock Metamorphic RockConglomerate/Breccia Gneiss

Conglomerate GneissShale Slate

Limestone MarbleLignite Hard coal (Anthracite)

Petrogenic or rock cycle• By James Hutton• Rocks can change from one type to another

Minerals• They compose rocks•Naturally formed elements and inorganic compounds whose atoms and molecules are bound together in a definite orderly arrangement to form crystals•Minerals can be composed of:1. Single elements – gold, carbon, silver, copper2. Compounds – oxides, sulfides, carbonates,

silicates, phosphates

Mineralogy• Study of minerals

Properties of Minerals• Color• Streak• Luster• Crystal form• Cleavage• Fracture• Specific Gravity (SG)•Hardness

Special Properties of Minerals•Magnetism• Electrical properties•Malleability•Ductility• Radioactivity

Color•Most obvious property• Ex. sulfur (yellow), malachite (green)•Unreliable because:1. Most minerals are colorless 2. Most minerals have the same color3. Impurities can alter color4. Chemical weathering can tarnish

the color

Color3. Impurities can alter

color

Ex. corundum is colorless.With traces of chromium, it becomes red (Ruby)With traces of titanium and iron, it becomes blue (Sapphire)

Streak• Color of mineral

in “powdered form” or when rubbed in an unglazed ceramic tile• More reliable

because same minerals have the same streak, even they differ in color.

Luster• Property to reflect or refract light• Metallic metals – shine when exposed

to light• Nonmetallic – do not shine

Crystal form• Atomic structure of the mineral• Atoms are arranged in definite geometric patterns•Amorphous minerals – atoms do not form a distinct pattern

Crystal form• Basic Types:1. Cubic 2. Tetragonal 3. Orthorhombic4. Monoclinic5. Triclinic6. Hexagonal(Descriptions in the next slide)

Cleavage and Fracture• Reveal the surface

of the mineral• Cleavage – natural

tendency to break along definite seams of weak bonding; even, planar and smooth breaking• Fracture – uneven,

nonplanar and irregular breaking

basal

prismatic

rhombohedral

prismatic

octahedral – cleavage in 4 directions

Types of Cleavage

Types of Cleavage

Basal (1 cleavage)

Prismatic (2 cleavages)

Types of Cleavage

Rhombohedral (3 cleavages, not 900)

Cubic(3 cleavages, 900)

Types of Cleavage

Octahedral(4 cleavages)

Dodecahedral(6 cleavages)

CleavageCleavage Type Examples

Basal Mica, GraphitePrismatic Feldspar

Rhombohedral CalciteCubic Halite, Table Salt

Octahedral FluoriteDodecahedral Pyrite

Types of Fracture

Fibrous – splintery/threadlike

Conchoidal – smooth, clam-like curves Hackly – sharp, irregular, jagged

Fracture

Fracture Type ExamplesConchoidal Obsidian, Quartz

Fibrous Asbestos, Satin Spar GypsumHackly Garnet

Cleavage

Cleavage

Fracture Cleavage (poor)

Specific Gravity• Tells how many times denser a given mineral is than an equal volume of water.

Gold has a specific gravity of 20.0. Therefore, 1 mL of gold is “20 times” heavier than 1 mL of water.

Diamond has a specific gravity of 3.5. Therefore, 1 mL of diamond is “3.5 times” heavier than 1 mL of water.

Hardness• Resistance to scratch•Mohs’ scale – test for hardness by Frederick Mohs

Mohs’ Scale of Hardness (Memorize)

Hardness

Mineral

1 Talc2 Gypsum3 Calcite4 Fluorite5 Apatite6 Orthoclase/

Feldspar7 Quartz8 Topaz9 Corundum10 Diamond

• 1 being the softest and 10 the hardest•Diamond (10) can scratch all the other minerals.• If a mineral can scratch fluorite (4) but not apatite (5), it has a hardness of 4.5. The same applies to other cases.

Magnetism• Ability to attract other minerals• Ex. magnetite

Electrical properties• Some minerals can become electrically charged when rubbed

Malleability• Ability of the mineral to be hammered into any desired shapes•Gold – most malleable metal

Ductility• Ability of the mineral to be drawn into very fine wires

Radioactivity• Ability of the some minerals to emit radiation• Ex. radium, thorium, uranium, cobalt

The Soil• The result of the process of

the gradual breakdown of rocks (due to erosion and weathering)• Vital to life on the planet• Four constituents: 1. Mineral matter – sand silt

and clay2. Organic matter – from

decomposed plants and animals

3. Air4. water

Sources• Science Links 7