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Minerals, Rocks, and
The Rock Cycle
22.2, 22.3
Minerals and Rocks
• A rock is a solid combination of minerals or
mineral materials
• A mineral is:
– Inorganic (not from living things)
– Solid
– Has a crystalline structure
– Characteristic chemical composition
– Building blocks of rocks
Classification
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Minerals are classified by:
Crystal structure; their geometric shape
Color
Streak; color of its powder
Luster; ability to reflect light
Density; mass/volume
Hardness; ability to avoid scratching
Fracture; how it breaks
Cleavage; type of fracture
Others include ability to dissolve in acid, electrical
properties, light refraction
Mohs Hardness Scale
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Talc
Gypsum
Calcite
Fluorite
Apatite
Orthoclase
Quartz
Topaz
Corundum
Diamond
Igneous Rocks
• Form from magma
• Magma that flows from volcanoes is called
lava
• Form when rock cools and solidifies
• Intrusive rocks cool inside the Earth, cool
slowly making large crystals
• Extrusive rocks cool outside the Earth,
cool rapidly
Intrusive Rocks
Gabbro, Granite
Extrusive Rocks
Obsidian, Basalt
Sedimentary Rock
• Weathering breaks down the Earth into
smaller pieces called sediment
• Sediment comes from living organisms or
rock
• Sedimentary rocks form over time when
sediment is squeezed and cemented
together
• Pressure causes the sediments to
compress
Clastic Rock
• Sedimentary rock that forms when other
rocks break and fracture
• Classified by size of particle which range
from pebble size to boulders
• Conglomerate rocks contain gravel and
pebbles and pieces are rounded
• Breccia is composed of sharp rock
fragments
Conglomerate, left
Breccia, right
Chemical Rock
• Form when rock precipitates out of a
solution
• Rain falls and dissolves rock, the minerals
are carried in streams, eventually the
streams can evaporate leaving new rock
behind, or the sediments settle forming
limestone
• Typically found in dry lake beds or caves
Limestone in Lehmann Caves,
Great Basin National Park, Eastern Nevada
Organic Rock
• Form when organisms die
• Shells and skeletons compress under
pressure and cement to form rock
Chalk Bluff
Along Truckee River
Reno, Nevada
Limestone, formed on ocean floor, left
• Limestone in White
Cliffs of Dover,
England, right
Metamorphic Rock
• Greek for “change form”
• Transformed by heat, pressure, chemical
reactions, and time
• Metamorphism can change the mineral content
as new rocks become embedded in the new
rock
• Change the texture and lead to layers
• Foliated rocks look like strips because the layers
are parallel
• http://www.learner.org/interactives/rockcycle/cha
nge2.html
Gneiss
Schist
Rock Type Quiz
• http://www.learner.org/interactives/rockcycl
e/types.html
The Rock Cycle
• http://www.learner.org/interactives/rockcycle/
diagram.html
Essential Questions
• What are the ten most common properties
that minerals are classified by?
• What are three groups into which rocks
are classified?
• What are the two ways igneous rocks can
form?
• What are the three groups of sedimentary
rocks called?
• How are metamorphic rocks formed?
References
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Gabbro image www.k12.nf.ca
Granite image marlimillerphoto.com
Obsidian, limestone images www.geology.com
Basalt image www.geologyclass.org
Conglomerate www.soil-net.com
Breccia flexiblelearning.auckland.a...
Lehmann Caves blog.roadtrippers.com
White Cliffs www.telegraph.co.uk
Metamorphic rock www.earth.ox.ac.uk