What are Minerals?
To meet the definition of "mineral" used by most geologists, a substance
must meet five requirements:
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Naturally occurring
Inorganic
Solid
Definite chemical composition
Orderly internal crystal structure
Minerals are distinguished by various chemical and physical properties.
Differences in chemical composition and crystal structure distinguish the
various species. All minerals have a unique and specific chemical
composition. This is like the DNA of the mineral - it's what makes the
mineral different from other minerals.
There are over 5,300 known mineral species; as of September 2017, over
5,290 of these had been approved by the International Mineralogical
Association (IMA).
The silicate minerals compose over 90% of the Earth's
crust. Silicon and oxygen constitute approximately 75% of the Earth's
crust; which means there are more silicate mineral
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The properties that can be used to identify minerals are:
Luster: this refers to the 'shininess' of the mineral (how light is reflected
off the surface)
Color: color can vary even within the same mineral, like corundum (it
can be white, blue or red), depending on what other elements are present.
Hardness: Ability to resist scratching not how easily it breaks. Hardness
depends on the bonds within the mineral, so the stronger the bonds, the
harder the mineral. Mineral hardness is measured on the Mohs scale of
hardness, which compares the hardness of different minerals.
Streak: a streak is the color, of the powdered form, of the mineral. (it can
be made by scratching a porcelain tile)
Cleavage and Fracture: is the way a mineral breaks apart. If it breaks
along smooth, flat surfaces or planes, it has cleavage. If it breaks with
rough or jagged edges, it has fracture.
Transparency: it can be transparent (see
through), translucent (shadowy), opaque (non-see through)
The Importance and use of Minerals
 Just about everything like computers, medicines, jewelry, copper
wiring, and electronics.
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Physical Properties – Luster
 Luster - the character of light reflected from the mineral
 A mineral’s luster may be metallic or non-metallic.
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Physical Properties – Color
 Color - the color of the mineral as it appears to the eye in reflected
light.
 Some minerals may have a range of colors. Example: quartz may be
color-less, white, pink, purple, dark brown, green, or blue.
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Physical Properties - Hardness
 Hardness - the resistance of a mineral to scratching. Hardness is
measured on a scale of 1 - 10 on the Mohs Scale of Hardness.
 Hardness of minerals can be determined by comparison to several
common objects – fingernail, copper object, nail, glass.
 Note: Pennies are no longer made of pure copper.
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Physical Properties – Crystal Form
 Crystal form - some minerals are in the form of crystals.
 Crystals "grow" through the addition of chemical ions to their
surfaces as they crystallize from magma or lava, mineral-rich waters,
or gases.
 Perfect crystals are rare in nature because they typically grow close
together in confined spaces, producing a mass of interlocking
crystals.
 A crystal growing in a larger space may develop crystal faces.
 Crystal shape is related to the structural arrangement of atoms
within the mineral.
All minerals can be divided into one of six crystal systems based on
symmetry. These systems use three or four imaginary lines, called axes, to
define the system based on the length of the axis and the angle that the
axes intersect.
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Crystal Forms
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Physical Properties – Mineral Habit
Mineral Habit – visible external shape of the mineral
Examples include acicular, bladed, prismatic, hexagonal, cubic, rosette,
botryoidal, striated, massive, radiating, twinning, & granular.
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Physical Properties – Cleavage and Fracture
Cleavage and Fracture - the way a mineral breaks when stressed
Cleavage – breakage in flat surfaces along planes of weakness
Several basic forms based on # directions
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One direction (basal)
Two directional
Three directional (not at right angles; rhombic)
Three directional (right angles or cubic)
Octohedral (4 – directions)
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Fracture - breaks in random directions (no planes of weakness)
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Mineral Classification
 Carbonates
 Native Elements
 Halides
 Oxides/Hydroxides
 Phosphates
 Sulfates
o Gypsum Varieties
 Sulfides
 Silicates
o Amphibole Group
o Feldspar – Plagioclase
o Feldspar – Potassium
o Garnet Group
o Mica Group
o Pyroxene Group
o Quartz Varieties
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Mineral Identification
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Carbonates
 Minerals made of carbon, oxygen, and a metallic element (contain
CO3);
 This group of minerals is soft and easily dissolved by even mild acids.
 Some of these minerals form by acidic action of air and rain
 Most fizz in acid.
 Reaction with HCl - Calcite, dolomite, malachite.
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Native elements
 Minerals made of a single element. Ex. copper, gold, graphite, sulfur,
silver
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Halides
 Form from halogen elements (chlorine, fluorine) with metallic
elements.
 Usually very soft and easily dissolved in water. Ex. Halite (NaCl) and
fluorite.
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Oxides
 Combination of a metal & oxygen
 Common ore minerals. Ex. Hematite (Fe), corundum (Al)
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Phosphates:
 Contain PO4
 Not as common. Ex. Apatite
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Sulfates :
 Compounds of sulfur with metals and oxygen
 Contain SO4 ;
 Often form in evaporative environments. Ex. Gypsum (calcium), barite
(barium), celestite (strontium)
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Sulfates – Gypsum Varieties
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Sulfides:
 Compounds of a metal with sulfur
 Common ore minerals. Ex. Galena (Pb), Sphalerite (Zn), Pyrite (Fe),
Chalcopyrite & Bornite (Cu, Fe)
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Silicates
 Made from metals combined with silicon and oxygen;
 Largest group of minerals; they make up over 90% of the weight of the
Earth’s crust.
 Quartz family of minerals are the most recognizable of this class.
 Silicon tetrahedron structure, most common mineral family, many
subgroups; some are very complex. Ex. Quartz, feldspars, micas,
olivine, hornblende, tourmaline, garnets, augite, talc, epidote, etc.
 Slightly changing the different elements that combine with silica
greatly changes the mineral that results, or the characteristics of the
mineral.
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Silicates – Amphibole Group
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Silicates –- Feldspar - Plagioclase
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Silicates –- Feldspar – Potassium
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Silicates –- Garnet Group
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Silicates –- Mica Group
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Silicates –- Pyroxene Group
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Silicates –- Quartz Varieties
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Rocks
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A rock is an aggregate of one or more minerals.
Rocks are the building blocks of the Earth's crust.
Rocks are classified by how they are formed.
There are three basic groups,
o igneous,
o sedimentary
o metamorphic
 In each group, distinctions are made for texture or grain size and
chemical or mineral content.
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How to classify between Igneous, Sedimentary and Metamorphic
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ROCK CYCLE
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Rocks Identification
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Igneous Rocks
 Igneous rocks get their name from the latin word for fire “igneus”
 These rocks are born of fire. Molten materials or Magma is hot molten
rock and are found below the earth crust; they are normally subjected
to extreme pressure and temperatures – up to 1200° Celsius.
 Magma also contains bits of rock crystals and gas. It ranges in
consistency from wet concrete to thick oatmeal.
 Due to extreme heat levels, igneous rocks do not contain organic
matter or fossils.
 Magma is made up of a fairly uniform mixture of elements. Some of the
major elements present are silica, iron, sodium, potassium, aluminum,
magnesium, and gasses including water vapor, oxygen, carbon dioxide,
nitrogen, hydrogen and sulfur dioxide.
 Lava is hot, molten rock that has flowed out and onto the surface of
the Earth.
 The rocks may be made up entirely of one mineral or various minerals,
and the cooling process determines their sizes.
 Igneous Rocks make up more than 90% of the Earth’s crust, by volume.
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Magma and Volcanoes
Rock that crystallizes from magma is IGNEOUS ROCK.
Factors controlling the behavior of Magma
1. Amount of Water
2. Amount of Silica
3. Temperature
Viscosity increases with
1. Increase in SiO2 (silica), because of the strong covalent silicon oxygen
bonds.
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2. Decrease in temperature.
3. Decrease in water. (water has a lubricating effect, breaking bonds,
making melting easier)
HOWEVER, added water causes explosive eruptions due to the
rapid expansion of water into steam (Subduction Zones).
Rock melts when the temperature within the earth (geotherm) exceeds the
melting point (solidus) of the rock.
This happens for different reasons at 1) subduction zone volcanoes 2) midocean ridge volcanoes and 3) hotspot volcanoes.
As continents collide, crust is pushed down, and melting begins.
The first minerals to melt are “granitic.” They rise up, but often cool, before
reaching the top of the mountain. These granitic batholiths become exposed
at surface when mountains erode.
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BOWENS REACTION SERIES
Minerals crystallize at different temperatures. Some are more stable than
others. As magma begins to cool, some minerals crystallize first changing
the composition of the magma.
The last minerals to crystallize are Quartz, sodium and potassium rich
feldspars and amphibole -> granite
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Classification of Igneous Rocks – By Texture and Composition
o Texture – Influenced by rate of cooling (fast or slow). Texture of
a rock is a description of the grain size.
o Composition – of a rock is dependent on the mineral
composition.
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There are two forms of silica
o Felsic – Feldspar and Silica – Form in granites and are lighter in
weight and color because they have less iron and magnesium.
o Mafic – Magnesium and Iron – Usually form in magmas moving
up to fill the gap left when tectonic plates are moving away from
each other on the sea floor. Basalt and Gabbro are this type.
Olivine and Pyroxene are ultramafic as they are relatively dark
and dense.
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Composition of Rocks (Felsic Mafic, Intermediate
and Ultramafic)
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Igneous rocks are of two types, Intrusive and Extrusive.
o Intrusive (Plutonic rocks) – formed by slow cooling of the
rocks beneath the earth’s surface. Texture is coarse grained.
o Extrusive (Volcanic rocks) – formed when rocks are quickly
cooled at Earth’s surface. Texture is fine grained.
 Volcanoes and Lavas
o Volcanoes are hills or mountains that form around the vent and
consist of cooled magma, rock fragments, and dust from
eruptions.
o Pieces of rocks that are blown out of volcanoes are called
pyroclasts or pyroclastic debris
o Pyroclastic flows are dense cloud like mixtures
o Crater is a circular depression at the top of the volcano
o 3 types of volcanoes
 Composite
 Built up over million years, they consist of alternating
layers of pyroclastic debris and lava
 Located along the circum-pacific belt also known as
Ring of Fire and Mediterranean belt
 Shield
 Shield based volcanoes are broad cone shaped hills or
mountains made from cooled lavas
 A spatter cone is a smaller feature that usually
develops on a cooling lava flow from a shield volcano
 Cinder cone
 Is composed of pyroclastic material ejected from a vent
o Volcanic domes
 If magma is thick and viscous and does not flow easily, it
may form a volcanic dome
 Volcanic domes are steep sided and form near the vents,
creating a plug that trap gases and building internal
pressures which can lead to violent explosions
 Viscosity is the resistance to flow; lava with high viscosity
flows slower, lava with low viscosity spreads quickly
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Igneous Rock Identification
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Igneous Environments of Formation (Show textures)
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Extrusive Igneous Rocks (also known as Volcanic Rocks)
 Extrusive rocks are formed from lava, which cool quickly on the Earth's
surface.
 Two main kinds of volcanic eruptions Mafic Lava and
Felsic/Andesitic Lava
 Mafic Lava – Effusive/Gushing lava eruptions
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Intrusive Igneous Rocks (Also known as Plutonic Rocks)
 Intrusive igneous rocks are formed when the magma cools off slowly
under the earth’s crust and harden into rocks. E.g. Gabbro and
Granite
 Rapid or fast cooling results in smaller crystals while slow cooling
results in large crystals.
 Intrusive rocks are very hard in nature and are often coarse-grained.
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Sedimentary Rocks
 Sedimentary Rocks cover about 75% of the world’s land area
 They are formed when loose sediment (gravel, sand, silt or clay)
becomes compacted and or cemented to form rock
 Every rock grain initially separated from other rocks. After many years
the materials finally settle down through the process of
Sedimentation. As the materials move they are smoothened and
rounded by abrasion.
 They leave pore spaces as they settle down which makes them achieve
their distorted shape.
 Cementation is gluing of rock pieces together by salt compounds or
organic matter.
 The process of converting sediment to sedimentary rock is called
lithification
 Sediment is deposited in horizontal layers called beds or strata
Weathering to Sedimentary Rocks
How common are Sedimentary Rocks
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Distinguishing characteristics of Sedimentary Rocks
Layers of sediments
Grains cemented together
Fossils
Textures of Sedimentary Rocks
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Sedimentary Rocks Identification
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Clastic – Compacted and cemented rock fragments; sediments derived
from continents Examples – Shale, sandstone, conglomerate and
breccia
Organic (Bioclastic) – Examples – Limestone (oolitic, fossil), Coal
(bituminous and anthracite)
Chemical/Biochemical – Examples – Gypsum, rock salt,
dolostone, travertine limestone
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Clastic – Compacted and cemented rock fragments.
 Sediments derived from continents. They are Inorganic
 Composed of clay minerals, quartz, feldspar, other mineral & rock
fragments
 Formed by compaction & cementation of grains
 Rock fragments
 Continental Environments include rivers, alluvial fans, desert sand
dunes, deltas, beaches, lakes
 Rock type depends on grain size
 Fossils may be present, particularly in shale and sandstone
E.g. Shale, sandstone, conglomerate and breccia
Breccia – Angular
fragments mixed pebble
size and smaller
Sandstone – sand sized; mostly quartz
Conglomerate – rounded
fragments; mixed pebble
size and smaller
Shale – clay sized particles
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Organic Sedimentary Rocks
 Formed from remains of plants or animals
 Often monominerallic
 If limestone, fizz in acid
 Many types of limestones due to various environments
 May or may not have visible fossils
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Organic – Coal
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Composed of carbon
Coal forms by compression and carbonization of plant material
Bituminous Coal is most common
Most coal formed 300 million year ago in swamp environments where
vegetation was abundant
 Anthracite Coal is the most pure form of coal (92-98% carbon) and
burns the most efficiently. It formed during mountain building
episodes when bituminous coal was under heat and pressure. It is often
considered a metamorphic rock, but is still found in sedimentary
sequences of sandstone and shale.
Bituminous Coal
Anthracite Coal
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Organic – Limestone
 Composed of calcium carbonate (calcite or aragonite)
 Most formed in marine environment from skeletal remains (shells,
algae, forams)
 Size of grains & types of fossils indicates environment
Types of Limestone
Coquina – composed of shell fragments 2mm or larger; forms in high
energy, shallow marine environment (beach)
Fossil Limestone – any limestone containing fossils; may be fine grained
or coarse grained; usually shallow marine
Oolitic Limestone – formed from small spherical grains (oolites) with
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concentric layers; formed in very shallow marine, high energy intertidal
environment or sometimes on lakebed by wave action. Right: enlarged view
of modern oolites from the Bahamas
Chalk and Diatomite
 Chalk and Diatomite are organic sedimentary rocks composed of the
shells of microscopic one celled photosynthetic protists
 Both rocks are light colored and powdery
 Chalk is a type of limestone, formed from forams and coccoliths
 Chalk is composed of calcite and will bubble with acid
 Diatomite is composed of the remains of diatoms
 Diatom skeletons are composed of opal (silica); diatomite is less dense
than chalk and will not bubble with acid
 Chalk formed in moderately deep marine environments
 Diatomite formed in lake or marine environments
Chalk is composed of coccoliths
Chalk is
composed of
coccoliths
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Diatomite is
composed of
Diatoms
Travertine
 Limestone formed from precipitation of calcite or aragonite in springs
or caverns
 Often appears as layers of crystals
 It is a chemical/crystalline form of limestone
 Often used as building material
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Chemical Sedimentary Rocks
 Crystalline rocks composed of one mineral
 Rock salt (Halite) and Gypsum form by the evaporation of water
(usually seawater) and the precipitation of dissolved minerals.
 Chemical sedimentary rocks that form by the evaporation of water are
called evaporites.
Rock Salt (Halite)
Rock Gypsum(Alabaster)
Chert and Dolostone
 Chert is a fine-grained silica rich microcrystalline sedimentary rock. It
is composed of quartz (SiO2). It often occurs as nodules in limestone or
chalk where it is believed to be a replacement mineral. It occurs in
layers as a primary deposit in some areas. The banded iron formations
of Precambrian age are composed of alternating layers of red chert
(jasper) with hematite.
 Chert comes in many colors, and the dark grey to black form is often
called flint.
 Dolostone is composed of the mineral dolomite and is often described
as a “non-descript” rock; looks like driveway gravel.
 Most dolostone formed when magnesium replaced calcium in
limestone or lime mud before lithification.
 Often has vugs with dolomite crystals
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Flint nodule in Chalk
Banded iron with red chert (jasper) and iron oxide
Dolostone – Looks fine grained and non-descript. Vug in dolostone with dolomite crystals
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Sedimentary Environments
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Environments in which Sedimentary Rocks are formed
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Sedimentary Texture Classification
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Metamorphic Rocks
 Metamorphic rocks form when pre- existing rocks (igneous,
sedimentary, or metamorphic) are exposed to high temperatures and
pressures under the Earth's surface.
 The word metamorphic means "changed form.”
 Metamorphic rocks can form from sedimentary, igneous, or
metamorphic rocks
 Metamorphism causes changes in the texture and mineralogy of other
rocks.
 Metamorphism results from:
o High temperatures,
o High pressures
o Chemical reactions
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How to Distinguish Metamorphic Rocks
The main thing about metamorphic rocks is that they are shaped by great heat and pressure.
The following traits are all related to that.
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Because their mineral grains grew together tightly during metamorphism, they're
generally strong rocks.
They're made of different minerals than other kinds of rocks and have a wide range of
color and luster.
They often show signs of stretching or squeezing, giving them a striped appearance.
There are two types of Metamorphism - Regional Metamorphism and Contact
Metamorphism
Regional Metamorphism – occurs when large areas of rocks are exposed to intense
pressure.
This occurs most often during
mountain building events, so
metamorphic rocks are found near
mountain ranges
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Four agents of Regional Metamorphism
Heat and Pressure - At high temperatures and pressures, the minerals in most rocks
break down and change into a different set of minerals that are stable in the new
conditions.
 Fluids – Most rocks contain some water, but Sedimentary rocks holds the most
o Metasomatism – Process which changes rock’s chemistry as well as its mineral
assemblage. Sedimentary rocks hold the most water, when they change back to
feldspar and mica, water is liberated by clay minerals. This water can become so
charged with dissolved materials that the resulting fluid is, in essence, a liquid
mineral may be acidic or alkaline, full of silica (forming chalcedony) or full of
sulfides or carbonates or metal compounds, in endless varieties. Fluids tend to
wander away from their birthplaces, interacting with rocks elsewhere.
 Strain – Change in shape of rocks due to force of stress
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Foliation and Non-Foliation
Foliation is a property of metamorphic rocks that have parallel wavy layers. Sometimes the
parallel layers form alternating bands of light and dark colors, this is called banding.
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Foliation is a property
of Metamorphic rocks
that have parallel wavy
lines
Banding is a property of Metamorphic
rocks that have wavy layers that
alternate between light and dark colors
Contact Metamorphism – occurs when hot magma forces its way up into the crust. When this
happens the heat cooks the rocks nearby causing metamorphism
Eventually the magma will cool
and become a layer of igneous
rock that cuts into the rocks
around it. This is called an
igneous intrusion. Contact
metamorphism rarely reaches
more than 100m from the
igneous intrusion.
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Metamorphic Rocks Identification
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Metamorphic Rock Classification
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