Rocks and Minerals

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Rocks and Minerals
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Elements, Compounds and Mixtures

• Matter is anything that takes up space and has
  mass.
• All matter can be classified into three forms
  elements, compounds and mixtures.

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Element

• An element is a substance that cannot be
  separated into simpler substances by ordinary
  chemical means. Scientists have identified 109
  elements.
• Each element has a name and a chemical symbol
  made up of one or two letters.
• The smallest part of an element that has all the
  properties of that element is an atom.

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Molecules

• Some elements are made up of atoms that are
  chemically combined to form molecules.
• A molecule is two or more atoms held together by
  chemical forces.

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Atomic Structure

• Atoms are made up of three main particles
  protons, neutrons and electrons. The center of
  the atom is called the nucleus. Two different
  kinds of particles are found in the nucleus. One
  of these is the proton.the proton is a positively
  charged particle. The other particle that makes
  up the nucleus is the neutron. A neutron is a
  neutral particle.

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Compounds

• A compound is made of atoms of different elements
  that are bonded together. Water is a compound.
  Some compounds are made up of aluminum,
  magnesium, silicon, oxygen and hydrogen.

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Mixtures

• Some forms of matter are neither elements nor
  compounds. Instead they are two or more
  substances mixed together. Such forms of matter
  are called mixtures. A mixture is two or more
  substances physically combined. Most rocks,
  soil, sea water and air are examples of mixtures.
  Because the substances that make up a mixture
  are not chemically combined they can be separated
  by physical means.

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Chemical Formulas

• The combinations of chemical symbols that
  represent atoms are called chemical formulas.
• A chemical formula shows that elements that make
  up a compound. A chemical formula also shows the
  number of atoms of each element in a molecule or
  smallest particle of the compound.

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Subscripts

• Subscripts give the number of atoms of the
  element in the compound. Subscripts are placed
  to the lower right of the symbols.

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Minerals

• A mineral is a naturally occurring, inorganic
  solid that has a definite chemical composition
  and crystal structure. In order for a substance
  to be called a mineral, it must have all five of
  the characteristics described in this definition.

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Inorganic

• A mineral must be inorganic, or not formed from
  living thing or the remains of living things.

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Solid

• A mineral is always a solid. Like all solids, a
  mineral has a definite volume and shape.

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Chemical Composition

• A mineral has a definite chemical composition. A
  mineral may made of a single pure substance, or
  element, such as gold, copper or sulfur. Most
  minerals are made of two or more elements
  chemically combined to form a compound.

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Crystal Structure

• A minerals atoms are arranged in a definite
  pattern repeated over and over again. Atoms not
  confined, the repeating pattern of a minerals
  atoms forms a solid called a crystal. A crystal
  has flat sides that meet in sharp edges and
  corners. All minerals have a characteristic
  crystal structure.
• There are 2500 different kinds of minerals.

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Formation and Composition of Minerals

• Many minerals come from magma, the molten rock
  beneath the Earths surface. When magma cools,
  mineral crystals are formed. How and where magma
  cools determine the size of the mineral crystals.
  When magma cools slowly beneath the Earths
  crust, large crystals form. When magma cools
  rapidly beneath the Earths surface, small
  crystals for

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Crystal Formation

• Crystals may also form from compounds dissolved
  in a liquid such as water.When the liquid
  evaporates, or changes to a gas, it leaves behind
  the minerals as crystals. Halite, or rock salt,
  forms in this way.

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Most Abundant Elements

• The eight most abundant elements in the Earths
  crust are oxygen, silicon, aluminum, iron,
  calcium, sodium, potassium and magnesium. There
  are about 100 common minerals formed from the
  eight most abundant elements.Of these 100, fewer
  than 20 are widely distributed and make up almost
  all the rocks in the Earths crust.

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Identifying Minerals

• Minerals have certain physical properties that
  can be used to identify them, such as color,
  luster, hardness, streak, density, crystal shape,
  and other special properties.

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Color

• The color of a mineral is an easily observed
  physical property. Color can be used to identify
  only those few minerals that always have their
  own characteristic color, such as malachite which
  is always green. The mineral azurite is always
  blue.
• Many minerals come in a variety of colors. Some
  are colorless.Colors can also change.

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Luster

• The luster of a mineral describes the way a
  mineral reflects light from its surface. Certain
  minerals have a metallic luster, such as silver,
  copper and gold. Minerals that do not reflect
  light have a nonmetallic luster, and are
  described by terms like glassy, pearly, dull and
  silky.

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Hardness

• The ability of a mineral to resist being
  scratched is known as its hardness. Hardness is
  one of the most useful properties for identifying
  minerals. Friedrich Mohs, a German mineralogist,
  worked out a scale of hardness for minerals
  ranging from 1 to 10. The number one is assigned
  to the softest mineral, talc and 10 is assigned
  to the mineral, diamond.

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Streak

• The color of the powder scraped off a mineral
  when it is rubbed against a hard , rough surface
  is called its streak. The streak may be
  different from the color of the mineral. Streak
  can be observed by rubbing the mineral sample
  across a piece of unglazed porcelain, which is
  called the streak plate. A streak plate has a
  hardness slightly less than 7.

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Density

• Density is the amount of matter in a given space.
  The density of a mineral is always the same, not
  matter what the size of the mineral sample.

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Crystal Shape

• Minerals have a characteristic crystal shape that
  results from the way the atoms or molecules come
  together as the mineral is forming. There are
  six basic shapes of crystal structures cubic,
  hexagonal, orthorhombic, monoclinic, tetragonal
  and triclinic.

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Cleavage and Fracture

• The terms cleavage and fracture are used to
  describe the way a mineral breaks. Cleavage is
  the tendency of a mineral to split along smooth,
  definite surfaces. Some minerals, like halite,
  break into small cubes. Micas cleave along one
  surface, making layers of thin sheets. Most
  minerals do not break along smooth lines.

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Special Properties

• Some minerals can be identified by special
  properties. Magnetite is naturally magnetic.
  Fluorite glows under ultraviolet light. Halite
  tastes salty. Sulfur smells like rotten eggs.
  Calcite fizzes when hydrochloric acid is added to
  . Uraninite is radioactive.

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Ores

• The term ores is used to describe minerals or
  combinations of minerals from which metals and
  nonmetals can be removed in usable amounts.

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Metals

• Metals are elements that have shiny surfaces and
  are able to conduct electricity and heat. Metals
  can be pressed or hammered into thin sheets and
  other shapes without breaking. Metals cans also
  be pulled into thin strands. Iron, lead,
  aluminum, copper, silver and gold are examples of
  metals.

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Smelting

• Most metals are found combined with other
  substances in ores. After the ores are removed
  from the Earth by mining, the metals must be
  removed from the ores. During a process, called
  smelting, an ore is heated in such a way that the
  metal can be separated from it. Metals are
  useful. Copper is used in pipes and electrical
  wire.

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Nonmetals

• Nonmetals are elements that have dull surfaces
  and are poor conductors of electricity and heat.
  Nonmetals are not easily shaped. Some are
  removed from the Earth in usable form. Others
  must be processed. Sulfur,a nonmetal, is used to
  make matches, fertilizers and medicines.

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Gemstones

• Gemstones are minerals that are hard, beautiful
  and durable and can be cut and polished for
  jewelry and decoration. Once a gemstone is cut
  and polished, it is called a gem. The rarest and
  most valuable gemstone- diamonds, rubies,
  sapphires and emeralds, are known as precious
  stones. All other gemstones, amethysts, zircons,
  garnets, are known as semiprecious stones.

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Rocks

• A rock is a hard substance composed of one or
  more minerals. A rock can also be made of or
  contain naturally occurring substances that do
  not perfectly fit the definition of a mineral.
  Rocks can be composed of volcanic glass or of
  opal. Both of these substances lack a
  crystalline structure.

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Types of Rocks

• Geologists place rocks into three groups
  according to how they form igneous, sedimentary
  and metamorphic.

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Igneous Rocks

• Igneous rocks were originally hot, fluid magma
  within the Earth. Igneous get their name from
  the Latin word, ignis, which means fire.

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Sedimentary Rock

• Most sedimentary rocks are formed from particles
  that have been carried along and deposited by
  wind and water. These particles, or sediments,
  include bits of rock in the form of med, sand or
  pebbles. Sediments also include shells, bones,
  leaves, stems and other remains of living things.
  Over time they are pressed together to form
  rocks.

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Metamorphic Rocks

• Metamorphic rocks are formed when chemical
  reactions, tremendous heat and great pressure
  change existing rocks into new kinds of rocks.
  These new rocks have chemical and physical
  properties usually quite different from the
  original rocks.

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Rock Cycle

• The continuous changing of rocks from one kind to
  another over long periods of time is called the
  rock cycle. The rock cycle has no definite
  sequence. It can follow many different pathways.

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Granite and the Rock Cycle

• Because granite is made of hard materials it is
  resistant to natures forces. It can be slowly
  worn down until bits of granite flake off and
  fall in streams and are eventually reduced to
  sand. The sand from granite, along with other
  sediments is carried to the sea and is deposited
  on the floor. The weight of layers piling on
  puts pressure on lower layers and with calcite
  the granite becomes part of a sedimentary rock.
  After many years, under great pressure and
  temperature the sedimentary rock will change to
  a metamorphic rock, quartzite

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Fluid and Fire Igneous Rocks

• Igneous rocks are classified according to their
  composition and texture.
• Composition refers to the minerals of which rocks
  are formed.
• Texture means the shape, size, arrangement and
  distribution of the minerals that make up rocks.
• Both are evident in a rocks appearance.

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Igneous Rock Textures

• Igneous rocks have four basic types of textures
  glassy, fine-grained, coarse-grained and
  porphyritic.

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Glassy Igneous

• Glassy igneous rocks are shiny and look like
  glass. The minerals that make up a glassy
  igneous rock are not organized into crystals.
  Obsidian has a glassy texture.

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Fine-Grained Igneous

• Fine-grained rocks, unlike glassy rocks, are
  made of interlocking mineral crystals. These
  crystals are too small to be seen without the
  help of a microscope. The dark gray rock known
  as basalt has a fine-grained texture.

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Coarse-Grained Rock

• Coarse-grained rocks, such as granite, consist of
  interlocking mineral crystals, which are all
  roughly the same size and visible to the unaided
  eye.

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Porphyritic Igneous Rocks

• Porphyritic rocks consist of large crystals
  scattered on a background of much smaller
  crystals. Sometimes these small background
  crystals are too tiny to be seen with a
  microscope. Porphyritic rocks have a texture
  that resembles rocky road ice cream.

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Igneous Variety

• Where and how magma cools determines the size of
  mineral crystals. The longer it takes magma to
  cool, the larger are the crystals that form.
  Glassy and fine-grained rocks form from lava that
  erupts from volcanoes and hardens on the Earths
  surface. Coarse-grained rocks form from molten
  rock that cools and hardens within the Earth.

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Extrusive Rocks

• Rocks formed from lava are called extrusive
  rocks. Because lava is brought to the surface by
  volcanoes, extrusive rocks are also known as
  volcanic rocks. Basalt and obsidian are two kinds
  of extrusive rocks that are quite solid. Pumice,
  another extrusive rock, is filled with bubbles.

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Intrusive Rocks

• Igneous rocks formed deep within the Earth are
  called intrusive. They form when magma forces
  its way upward into preexisting rocks and then
  hardens. Intrusive rocks include granite and
  pegmatite. Intrusive rocks are also known as
  plutonic rocks. A mass of intrusive rocks are
  known as a pluton. Plutons may produce landforms
  by pushing up layers of rock above them, such as
  domes.

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Slowly Built Layers Sedimentary Rocks

• The most widely used classification system for
  sedimentary rocks places them into three main
  categories according to the origin of the
  materials from which they are made. These three
  categories are clastic rocks, organic rocks and
  chemical rocks.

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Clastic Rocks

• Sedimentary rocks that are made of the fragments
  of previously existing rocks are known as clastic
  rocks. Clastic rocks are further classified
  according to the size and shape of the fragments
  in them.

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Conglomerates

• Some clastic rocks are made of rounded pebbles
  cemented together by clay, mud or sand. If over
  a third of the rock is made of pebbles, the rock
  is called a conglomerate. The pebbles in
  conglomerates are smooth and rounded because they
  have been worn down by the action of water. They
  are also called puddingstones.

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Sandstones

• Clastic rocks made of small, and-sized grains are
  called sandstones. At least half the particles
  in a clastic rock must be sand sized in order for
  it to be considered a sandstone. Sandstones are
  very common rocks. They are formed from the sand
  on beaches, in riverbeds and in sand dunes. In a
  sandstone, the grains are cemented together by
  minerals that harden.

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Shale

• Many geologists use term shale to describe all
  the clastic rocks that are made of particles
  smaller than sand. Shale forms from small
  particles of mud and clay that settle to the
  bottom of quiet bodies of water such as swamps.
  Most shale can be split into flat pieces.

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Organic Rocks

• Organic rocks come from organisms.Limestone are
  often but not always organic rocks. Deposits of
  limestone may be formed from the shells of
  creatures when they die. Creatures may also
  cement their shells together and over time form
  reefs. Coal is also made from the remains of
  living things. It is made from plants that lived
  millions of years ago.

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Chemical Rocks

• Some sedimentary rocks are formed when a sea or
  lake dries up, leaving large amounts of minerals
  that were dissolved in water. Examples of
  chemical rocks formed this way include rock salt
  and gypsum. Some limestone rocks are formed by
  inorganic processes in caves. As water
  evaporates, a thin deposit of limestone is left
  behind.

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Changes in Form Metamorphic Rocks

• When already existing rocks are buried deep
  within the Earth, tremendous heat, great pressure
  and chemical reactions may cause them to change
  into different rocks with different textures and
  structures. The changing of one type rock into
  another as a result of heat, pressure and /or
  chemical reactions is called metamorphism.

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Metamorphic Rocks

• Metamorphic rocks may be formed from igneous,
  sedimentary or metamorphic rocks. Heat and
  pressure are great enough to make tock undergo
  change. Temperatures of 100 degrees to 800
  degrees cause some minerals to break down,
  allowing their atoms to form other more
  heat-tolerant minerals.Texture, mineral and
  chemical composition may change.

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Metamorphic Rocks

• The amount of heat, pressure and chemical
  reactions varies during metamorphism. Thus the
  degree of metamorphism also varies. The
  characteristics of the original rock also affect
  the degree of metamorphism. Many metamorphic
  rocks can be produced from more than one kind of
  rock.

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Metamorphic Classification

• Like igneous and sedimentary rocks, metamorphic
  rocks can be classified according to texture.
  The classification for metamorphic rocks are
  based on the arrangement of the grains that make
  up the rocks.

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Foliated Rocks

• In the first group, the mineral crystals are
  arranged in parallel layers, or bands. The word
  foliated comes from the Latin word for leaf. It
  describes the layers in such metamorphic rocks,
  which are thin and flat. Most metamorphic rocks
  are foliated, like schist, slate and gneiss.

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Unfoliated Rocks

• In the second, smaller group of metamorphic
  rocks, the rocks are not banded and do not break
  into layers. These rocks are said to be
  unfoliated. Marble and quartzite are examples of
  unfoliated rocks.