Rocks and minerals

• Chemical Analysis– 8 elements make up 98.6% of the crust – These 8 elements make up the solid materials of the Earth’s crust and are known as rocks and minerals.. – A mineral is solid

•Rocks and Minerals

• No other planet in the solar system has the unique

combination of fluids of Earth Earth has a surface that is mostly covered with liquid water, water vapor

in the atmosphere, and both frozen and liquid water

on the land.

• Solid Earth Materials

• Earth’s Molten Stage

– During the early formation of the Earth it was molten– During this stage the heavier elements such as iron and nickel, sank to the deeper interior of the Earth

– This left a thin layer of lighter materials on the surface that is mow called the crust

– The majority of the Earth’s mass lies below the crust

• Chemical Analysis

– 8 elements make up 98.6% of the crust

– These 8 elements make up the solid materials of the

Earth’s crust and are known as rocks and minerals

– A mineral is solid inorganic material of the Earth that

has both a known chemical composition and a crystalline structure that is unique to that mineral

– A rock is a solid aggregate of one or more minerals that have been cohesively brought together by a rock-forming process

• (A)The percentage by weight of the elements that make up Earth's crust (B) The

percentage by weight

of the elements that

make up the whole

Earth.

• Minerals

• Introduction

– Minerals

• A mineral is solid inorganic material of the Earth that has both

a known chemical composition and a crystalline structure that

is unique to that mineral

– Rocks

• A rock is a solid aggregate of one or more minerals that have been cohesively brought together by a rock-forming process.

• A crystal is composed of a structural unit that is repeated in three dimensions This is the basic structural unit of a

crystal of sodium chloride, the mineral halite

• The structural unit for a crystal of table salt, sodium

chloride, is cubic, as you can see in the individual grains

• These quartz crystals are hexagonal prisms.

• Crystalline substances are

classified into six major systems: isometric, hexagonal, tetragonal, orthorhombic, monoclinic, and

triclinic The six systems are

based on the arrangement of

crystal axes, which reflect how

the atoms or molecules are

arranged inside For example,

crystals in the orthorhombic

system have three axes of

different lengths intersecting at

90O angles while crystals in the

hexagonal system have three

horizontal axes intersecting at 60O and one vertical axis Some

common examples in each system are illustrated here

• (A)The geometric shape

of a tetrahedron with

four equal sides (B) A silicon and four oxygen atoms are arranged in the shape of a tetrahedron

with the silicon in the

center This is the basic building block of all

silicate minerals.

• (A)Isolated silicon-oxygen tetrahedra do not share oxygens This structure occurs in the mineral olivine (B) Single

chains of tetrahedra are formed by each silicon ion having two oxygens all to itself and sharing two with other silicons

at the same time This structure occurs in augite (C) Double chains of tetrahedra are formed by silicon ions sharing

either two or three oxygens This structure occurs in

hornblende (D) The sheet structure in which each silicon shares three oxygens occurs in the micas, resulting in layers that pull off easily because of cleavage between the sheets

• Silicates and Nonsilicates

– silicates that do not contain either iron or magnesium.

– Lower density and lighter color than the ferromagnesian silicates.

• Compare the dark colors of the ferromagnesian silicates augite (right), hornblende (left), and biotite to the light-colored nonferromagnesian silicates.

• Compare the light colors of the nonferromagnesian silicates mica (front center), white and pink orthoclase (top and

center), and quartz, to the dark-colored ferromagnesian

silicates

– Nonsilicates – make up 8% of Earth’s crust

• Physical Properties of Minerals

• This is the color of the mineral when it is finely powdered.

• Rubbed across a piece of tile, leaving a fine powder of the mineral on the tile.

– Hardness

• Resistance of the material to being scratched.

• Measured using the Mohs hardness scale, which compares the hardness of the mineral to 10 reference minerals.

• (A)Gypsum, with a hardness of 2, is easily scratched

by a fingernail (B) Quartz, with a hardness of 7, is

so hard that even a metal file will not scratch it.

– Crystal form

• Related to the internal geometric arrangement of the atoms that make up the crystal structure.

– Cleavage

• the tendency of mineral to break along smooth planes.

• Depends upon zones of weakness in the crystal structure.

– Fracture

• The broken surface is irregular and not in a flat plane.

– Luster

• Surface sheen

• Metallic – like metal

• Pearly – like pearl

• Vitreous – like glass

• Earthy

– Density – ratio of the mass of a mineral to its volume

• Specific gravity – ratio of mineral density to the density of water

• Depends on:

– Kind of atoms which make up the mineral– How the atoms are arranged in the crystal lattice

• Mineral-forming Processes

• Minerals Formed at High Temperatures

– Bowen’s Reaction Series

• Arranged with minerals at the top that crystallize at higher temperature and minerals at the bottom that crystallize out at lower temperature

• Bowen's reaction series Minerals at the top of the series

(olivine, augite, and calcium-rich plagioclase) crystallize at higher temperatures, leaving the magma enriched in silica Later, the residual magma cools and lighter-colored, less

dense minerals (orthoclase feldspar, quartz, and white mica) crystallize Thus, granitelike rocks can form from a magma that would have produced basaltic rocks had it cooled

quickly

• Minerals Formed at Normal Temperatures

– These form at normal temperatures and pressures and in contact with atmospheric gases such as oxygen, carbon dioxide, and water

– There are most of the non-silicates; carbonates, sulfates, oxides, halides, and sulfides

• Altered Minerals

– These minerals undergo changes in chemistry or crystal structure as a result of pressure, temperature, or chemical solutions

– Similar to minerals that form under high temperatures

with similar physical properties

• Ore Minerals

– Some minerals are left over after the crystallizing of

magma

– These elements are flushed away in hot water solutions

as the magma crystallizes

– Usually crystallize in rock fractures to form thin, flat bodies of mineral material called veins

– If these minerals have some economic value they are called ore minerals

• Rocks

• Introduction

– Elements are chemically combined to form minerals– Minerals are physically combined to form rocks

• Igneous Rocks

– Form from molten rock material

– Intrusive igneous rock

• Formed when magma cools deep within the Earth’s surface

• Cools very slowly as it is in contact with molten rock.

• Produces course-grained igneous rock.

– Extrusive igneous rock

• Magma that cools above the Earth’s surface.

• Produces fine-grained igneous rocks.

• This rapid cooling does not allow time for crystals to form.

• Igneous rock classification scheme based on mineral

composition and texture There are other blends of minerals with various textures, many of which have specific names

• Granite is a coarse-grained igneous rock composed mostly

of light-colored, light-density, nonferromagnesian minerals The earth's continental areas are dominated by granite and

by rocks with the same mineral composition of granite

• This is a piece of obsidian, which has the same chemical

composition as the granite Obsidian has a different texture because it does not have crystals and is a volcanic glass The curved fracture surface is common in noncrystalline

substances such as glass

• Sedimentary Rocks

– Form from material from previously existing rock

• Material is provided by weathering of previously existing rock

– Sediments

• Weathered rock materials

• Dissolved rock materials

– Clastic sediments

• Another name for weathered rock materials

• This is a sample of breccia, a coarse-grained

sedimentary rock with coarse, angular fragments Compare the grain sizes to the centimeter scale.

• This is a sample of sandstone, a sedimentary rock that

formed from sand grains in a matrix of very fine-grained silt, clay, or other materials The grains in this sample are mostly the feldspar and quartz minerals, which probably accumulated near the granite from which they were eroded

• This is a sample of limestone, a sedimentary rock made of calcium carbonate that formed under water directly or

indirectly from the actions of plants and animals This grained limestone formed indirectly from the remains of tiny marine organisms

fine-– Chemical sediments

• Another name for dissolved rock material

• The dissolved materials are ions from mineral and rocks that have been completely broken down

• Removed from solution by:

– Chemical precipitation from the solution– Crystallization from evaporating water

– Biological sediments

– Compaction

• As sediments are laid down grain by grain, the mass becomes greater.

• The increasing mass of the sediment layer above creates

pressure on the layers below.

• Eventually this pressure becomes great enough to compact the existing layers into a cohesive rock layer.

• (A)In compaction, the sediment grains are packed more tightly together, often by

overlying sediments,

as represented by the bricks (B) In

• Metamorphic Rocks

– Rocks changed by heat, pressure, or hot solutions due to:

• Movement of the Earth’s crust

• Heat generated by intrusion of hot magma

• Pressure can change rock by flattening, deforming, or realigning mineral grains.

• Increasing metamorphic change occurs with

increasing temperatures and pressures If the melting point is reached, the change is no longer

metamorphic, and igneous rocks are formed.

• This is a sample of marble, a coarse-grained metamorphic rock with interlocking calcite crystals The calcite crystals were recrystallized from limestone during metamorphism.

• This banded

metamorphic rock is very old; at an age of 3.8 billion years, it is probably among the oldest rocks on the surface of the earth.

• The Rock Cycle

• Earth is a dynamic planet with the surface and

interior in a constant state of flux.

– Internal changes alter the surface by moving the Earth’s plates, building mountains

– Seas advance and retreat over the continents brining in new materials and taking other materials away

– Rocks are continually being changed by Earth’s forces

• The Rock Cycle describes the continually changing structure of rocks.

– Igneous, sedimentary, or metamorphic rock are just

temporary stages in the continuing changes that all rocks undergo

• A schematic diagram of the rock cycle concept, which states that geologic processes act

continuously to produce new rocks from old ones.