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MineralsRocks
igneoussedimentarymetamorphic
Minerals and rocksChapter 2
Minerals form rocksThree rock types have different properties because they form in
unique waysRock cycle interrelates all rocks
Environmental Geology [email protected]
MINERALS Naturally occurring Inorganic Solid element or compound Definite chemical composition Regular internal crystal structure Identified by recognizing different physical properties
Figure 2.4B Figure 2.4C
Identifying Minerals The two fundamental
characteristics of a mineral are its chemical composition and its crystal structure
Analyze the mineral composition• Technology based
Measure crystal structure and symmetry• Technology based
Observe and measure physical and special properties• Easy for humans to see and
recognize
Color Hardness Cleavage Luster Density Form
Table 2.1
Rocks – formed from Minerals A solid aggregate of one or more minerals, or mineral
materials Consists of many mineral grains or crystals forming a solid
mass Each rock contains a record of its own history Three broad categories
• Igneous: cooled from melted magma• Sedimentary: deposited from physical or chemical parts• Metamorphic: altered from previous rocks
Three rock types each show a particular texture from the process of formation• Igneous: Crystalline and interlocking• Sedimentary: granular and layered• Metamorphic: warped, banded or squeezed
Igneous Rocksformed by the solidification and crystallization of a cooling
magma Rocks formed from hot, molten rock material [magma] Usually composed of silicate minerals + some
dissolved gases + water Plutonic rocks form if magma cools inside earth’s crust
(does not flow onto surface); coarse crystals will grow Volcanic rocks form if magma flows onto surface as
lava; glass often forms Coarse, visible crystals indicate time spent cooling =
depth underground
St Cloud GraniteSt Cloud, MN
1.7 + billion years old
Igneous RocksFelsic
low ironlight toned
Intermediate
Mafic
high irondark toned
Volcanic:Surface, fine grained
Rhyolite Andesite Basalt
Plutonic:Deep,coarse grained
Granite Diorite Gabbro
Sedimentary Rocks• Sediments are accumulations of mineral
or rock particles produced by weathering of pre-existing rocks and minerals
• Sediments are eroded, transported, and deposited and buried in many sedimentary environments
• Gravity and transport play a role in the formation of all sedimentary rocks
• Layering is a very common feature of sedimentary rocks and is used to identify the origins of sedimentary rocks
• Sedimentary rocks are formed at or near the earth’s surface and at temperatures close to ordinary surface temperatures. St Peter Sandstone
St Paul, MN455 million years old
Metamorphic Rocks “Changed form” rock Rock formed from pre-existing rock or
minerals Heat, pressure, and chemically active
fluids cause changes in rock Heat increases as a rock is buried or is
close to magma – not quite melting but can have big effect such as recrystallization
Pressure increases with burial or collision between moving continents and can cause deformation, recrystallization
Fluids become heated and circulate with burial or with location near a magma chamber
Morton GneissCentral MN
2.5 + billion years old
Common Metamorphic Rocks Any kind of preexisting rock (another rock) can be
metamorphosed Foliation: when a rock is subjected to directed
stress, its minerals form elongated/platy crystals and line up parallel to each other
Metamorphic rocks without foliation do not show directed stress• Marble is metamorphosed limestone• Quartzite is metamorphosed quartz-rich
sandstone Metamorphic rocks with foliation show directed
stress or pressure• Slate – low grade foliated metamorphic rock• Schist and Gneiss (nice) – high grade
metamorphic rocks
The Rock Cycle Shows the
interrelationships among the three rock types
Rocks of any type can be transformed into rocks of another type or into another distinct rock of the same general type through the geologic processes
Rocks are continually being changed by geological processes
