2014 09 08 rocks and minerals fall2014

Rocks and Minerals: Definitions– A mineral is solid inorganic material of the Earth that has both a known chemical composition and a crystalline structure that is unique to that minera

Rocks and

Minerals

8 September 2014

Rocks and Minerals: Definitions

– A mineral is solid inorganic material of the Earth that

has both a known chemical composition and a

crystalline structure that is unique to that mineral

– A rock is a solid aggregate of one or more minerals

that have been cohesively brought together by a forming process.

rock-Earth Interior: Physical

Mineral Composition

Minerals are grouped or classified based on their composition There are 6 groups

1 Carbonates - contain

carbon, oxygen, and one

ore more metallic element

atom and 4 oxygen atoms

- formed from cooling

3 Oxides

- Minerals that

contain oxygen and one or more other element(s)

5 Halides

-minerals containing

halogen ions plus

one or more other

elements

Halite

– Elements are chemically combined to form minerals– Minerals are physically combined to form rocks

Igneous Rocks

• Magma- molten material underground

• Lava- magma that reaches the surface

• Igneous rocks are formed from magma that has cooled and hardened either beneath the surface or from a volcanic eruption

2 Ways to Form Igneous Rock

Rocks- form when

lava hardens on the surface of the Earth

• Extruded onto the surface

granite

rhyolite

• Magma contains some gases, including

water vapor- this make it less dense, so it rises

• As magma rises, it cools and forms crystals

• The longer the cooling time the larger the crystals

• Granitic Composition- contain

mainly quartz and feldspar,

some with biotite mica and

amphibole Make up major

rocks of continental crust

• Basaltic Composition- contain

mainly dark colored minerals

and feldspar, along with Mg

and Fe Darker and denser than granitic composition

Igneous rock classification scheme based on mineral

composition and texture There are other blends of minerals with various textures, many of which have specific names

Granite is a coarse-grained igneous rock composed mostly

of light-colored, light-density, nonferromagnesian minerals The earth's continental areas are dominated by granite and

by rocks with the same mineral composition of granite

This is a piece of obsidian, which has the same chemical composition as the granite Obsidian has a different texture because it does not have crystals and is a volcanic glass The curved fracture surface is common in noncrystalline substances such as glass.

Sedimentary Rocks- formed from compacted and cemented sediments

• Weathering physically and chemically

breaks rocks into small pieces called

sediments

• Sediments are moved

by wind, water, ice,

and gravity

• Eventually, they are

dropped and form layers

that are cemented together

Weathering, Erosion, and

Compaction and Cementation

• Compaction is the

process that squeezes

the water out of the

sediments It is caused

by the weight of the

sediments

• Cementation takes

place when dissolved

minerals are deposited

in the tiny spaces

among the sediments

• Cementing holds the sediments together.

Classification of Sedimentary

Rocks- based on formation

• Clastic Sedimentary

Rocks are formed

from weathered bits of

rocks and minerals

Coquina limestone

• Sedimentary rocks hold many clues to the Earth’s history

• Layers of sediments are records of geologic events on Earth

• Fossils are unique to sedimentary rocks

This is a sample of breccia, a coarse-grained

sedimentary rock with coarse, angular fragments Compare the grain sizes to the centimeter scale

This is a sample of sandstone, a sedimentary rock that

formed from sand grains in a matrix of very fine-grained silt, clay, or other materials The grains in this sample are mostly the feldspar and quartz minerals, which probably accumulated near the granite from which they were eroded

This is a sample of limestone, a sedimentary rock made of calcium carbonate that formed under water directly or

indirectly from the actions of plants and animals This grained limestone formed indirectly from the remains of tiny marine organisms

fine-Metamorphic Rocks- form when existing rocks undergo change through

heat and pressure

• These occur deep below

the Earth’s surface and

extend into the mantle

close= more compact

rock= greater density

Increasing metamorphic change occurs with

increasing temperatures and pressures If the

melting point is reached, the change is no longer metamorphic, and igneous rocks are formed.

This is a sample of marble, a coarse-grained metamorphic rock with interlocking calcite crystals The calcite crystals were recrystallized from limestone during metamorphism.

– Seas advance and retreat over the continents

brining in new materials and taking other materials away.

– Rocks are continually being changed by Earth’s forces

A schematic diagram of the rock cycle concept, which states that geologic processes act

continuously to produce new rocks from old ones.

The Rock Cycle

float to top (differentiation)

• Radioactive heating declines; crust solidifies

• Tectonics, impacts, volcanism, erosion

modify surfaces (next lectures)