Transcript Rocks and Rock Cycle

Chapter 4
 Magma – hot, molten rock from the Earth’s interior is
the parent material for all rocks.
 Three Major Types of Rock
 Igneous Rock
 Sedimentary Rock
 Metamorphic Rock
 Any of the 3 major types of rock can be changed into
another type. Various geological forces and processes
cause the rock to change from one major type to another
and back again.
 Formed when magma cools and crystallizes.
 Most abundant rock on Earth
 Intrusive (Plutonic) – Igneous rocks that are formed
below the Earth’s surface
 Slow rate of cooling, which results in the formation of
large crystals (coarse-grained)
 Extrusive (Volcanic) – Igneous rocks that are formed at
the Earth’s surface.
 Rapid cooling – results in formations of small crystals
(fine-grained)
 Igneous rocks are classified by texture and mineral
composition.
 Texture – size, shape, and arrangement of interlocking
crystals
 Fine-grained
 Coarse-grained
 Porphyritic
 Glassy
 Extrusive Igneous Rock
 crystals to small to be seen by the unaided eye.
 Vesicles are common in fine-grained igneous rocks.
 Vesicles are voids that are left by gas bubbles that are
formed as the lava is solidified.
 Intrusive Igneous Rocks
 Formed below the Earth’s surface
 Slow cooling allowing for large crystals to form
 Crystals
 roughly equal in size
 Can be seen by the unaided eye
 When magma that already contains some large crystals
suddenly erupts at the surface, the remaining molten
portion of the lava would cool quickly.
 Resulting Rock
 Large crystals imbedded in a matrix of smaller crystals
 Formed during volcanic eruptions, molten rock is
ejected into the atmosphere, where it is cooled very
quickly.
 Igneous rocks are mainly composed of silicate
minerals.
 Dark Silicates – are rich in iron and/or magnesium and
are relatively low in silica.
 Olivine, pyroxene, amphibole, and biotite mica are
common dark silicates.
 Light Silicates – contain greater amounts of potassium,
sodium, and calcium
 Quartz, muscovite mica, and feldspars (most abundant
mineral group)
 Sedimentary rocks are formed by the process of
erosion.
 The weathering debris are constantly being swept away
from bedrock and carried away by water, ice, and wind
(aka. Erosion).
 The debris is eventually deposited into lakes, river
valleys, seas, and countless other places.
 As the sediments accumulate, the material near the
bottom are compacted by the weight of the overlying
layer. Over long periods of time, these sediments are
cemented together by mineral matter deposited from
water in the spaces between particles.
 Lithification – refers the processes by which sediments
are transformed into solid sedimentary rocks.
 Compaction – most common
 Cementation - minerals are carried in solution by water
seeping through the pore spaces between particles.
Over time, the cement precipitated onto the sediment
grains, filling the open spaces, joining the particles
together.
 Calcite, silica, and iron oxide are the most common cements
 Sedimentary rocks provide geologists with evidence of
Earth’s long history.
 Past environments
 Conglomerate – indicates high-energy environment, such as
rushing stream, where only a coarse material can settle out.
 Black Shale or Coal – associated with low-energy, organicrich environment such as a swamp or lagoon.
 Ripple marks – may indicate a beach or stream channel
environment
 Mud cracks – form when wet mud or clay dries and shrinks,
possibly signifying a tidal flat or desert basin.
 Fossils – traces of remains of prehistoric life, perhaps the
most important inclusions found in sedimentary rocks.
 Fossils are important tools used in interpreting the geologic past.
 Detrital Sedimentary Rocks – formed from weathering
rocks, such as igneous rocks.
 Mainly formed by clay minerals and quartz
 Geologists us particle size to classify detrital
sedimentary rocks.
 Chemical Sedimentary Rocks – formed when dissolved
substances are precipitated back as solids.
 Formed by material that is carried in solution to lakes
and seas.
 Limestone is the most abundant chemical sedimentary
rock (composed of calcite (CaCO3)).
 This process is the transformation of one rock type
into another caused by changes in temperature and
pressure (stress).
 Contact Metamorphism – alteration of a rock,
mainly by heat, that occurs near a heat source such as a
magma chamber
 Regional Metamorphism - metamorphism across a
broad area caused by the elevated temperatures and
pressure of plate collision or deep burial
 Foliated – caused by differential stress, the crystals will
recrystallize with preferred orientation, perpendicular
the direction of the compressional force.
 show bands due to pressure
 Nonfoliated – metamorphic rocks composed of only
one mineral with no banding