Earth Materials Minerals and Rocks

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Chapter 2
Earth MaterialsMinerals and Rocks
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Matter and Its Composition

• Matter
• anything that has mass and occupies space
• exists as solids, liquids, gases, and plasma
• consists of elements and atoms
• Element
• a chemical substance
• composed of tiny particles called atoms

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Atoms

• Atoms are the smallest units of matter
• that retain the characteristics of the element
• Atoms have
• a compact nucleus containing
• protons particles with a positive electrical
  charge
• neutrons electrically neutral particles
• particles outside the nucleus
• electrons negatively charged particles

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Atoms

• Atomic number
• the number of protons
• Atomic mass number
• number of protons number of neutrons
• The number of neutrons in nucleus of an element
  may vary

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Isotopes

• Isotopes
• the different forms of an elements atoms
• with varying numbers of neutrons
• Different isotopes of the same element
• have different atomic mass numbers
• Isotopes are important in radiometric dating

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Electrons and Shells

• Electrons lie outside the nucleus in one or more
  shells
• The outermost shells are involved
• in chemical bonding
• and contain up to 8 electrons
• Noble gas configuration of 8 electrons
• or 2 for helium
• have complete outer shells
• and are stable
• Other atoms attain
• a noble gas configuration
• in the process of bonding

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Bonding and Compounds

• Bonding
• the process whereby atoms join to other atoms
• Compound
• a substance resulting from the bonding
• of two or more elements
• Oxygen gas (O2) is an element
• Ice (H2O) is a compound
• made up of hydrogen and oxygen atoms
• Most minerals are compounds

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Ionic Bonding

• One way for atoms to attain the noble gas
  configuration
• is by transferring electrons, producing ions
• Ion
• an atom that has gained or lost one or more
  electrons
• and thus has a negative or positive charge
• Ionic bonding
• attraction between two ions of opposite charge

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Covalent Bonding

• Another way for atoms
• to attain the noble gas configuration
• is by sharing electrons

• Covalent bonding
• results from sharing electrons

shared electrons
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Minerals

• Geological definition of a mineral
• naturally occurring
• crystalline solid
• crystalline means that minerals
• have atoms arranged in specific 3-dimensional
  frameworks

• minerals have a narrowly defined chemical
  composition
• and characteristic physical properties

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MineralsThe Building Blocks of Rocks

• A minerals composition is shown by a chemical
  formula
• a shorthand way of indicating how many atoms of
  different kinds it contains

• Quartz molecules consist of 1 silicon atom and 2
  oxygen atoms

Quartz SiO2 Ratio 1 2

• Orthoclase molecules consists of 1 potassium, 1
  aluminum, 3 silicon, and 8 oxygen atoms

KAlSi3O8 1 1 3 8
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Native Elements

• A few minerals consist of only one element.
• They are not compounds.
• They are known as native elements.
• Examples

• Gold Au

• Diamond C

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Crystalline Solids

• By definition, minerals are crystalline solids
• with atoms arranged in a specific 3D framework
• If given enough room to grow freely,
• minerals form perfect crystals with
• planar surfaces, called crystal faces
• sharp corners
• straight edges

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Mineral Properties

• Mineral properties are controlled by
• Chemical composition
• Crystalline structure
• Mineral properties are particularly useful
• for mineral identification and include

• cleavage
• fracture
• hardness
• specific gravity

• color
• streak
• luster
• crystal form

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Silicates

• Silicates are minerals containing silica
• Si and O
• These minerals make up perhaps 95 of Earths
  crust
• and account for about 1/3 of all known minerals
• The basic building block of silicates
• is the silica tetrahedron
• which consists of one silicon atom
• surrounded by four oxygen atoms

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Types of Silicates

• Silica tetrahedra can be
• isolated units bonded to other elements
• arranged in chains (single or double)
• arranged in sheets
• arranged in complex 3D networks

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Types of Silicates

• Ferromagnesian silicates
• contain iron (Fe), magnesium (Mg), or both
• Nonferromagnesian silicates
• do not contain iron or magnesium

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Ferromagnesian Silicates

• Common ferromagnesian silicates include

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Nonferromagnesian Silicates
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Other Mineral Groups

• Carbonates
• minerals with carbonate ion (CO3)-2
• calcite (CaCO3),
• constituent of limestone
• dolomite CaMg(CO3)2,
• constituent of dolostone
• Other mineral groups are important,
• but more as resources
• than as constituents of rocks

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Rock-Forming Minerals

• Most rocks are solid aggregates
• of one or more minerals
• Hundreds of minerals occur in rocks,
• but only a few are common
• and called rock-forming minerals
• Most rock-forming minerals are silicates,
• but carbonates are also important
• Accessory minerals are present in small amounts
• and are ignored in classifying rocks