Earth Science Rocks

What is a Rock?

A group of minerals bound together!

Classification of Rocks

Igneous Rock Formed by the cooling and hardening of magma.

Sedimentary Rock Formed by layers of sediments.

Metamorphic Rock Formed by heat and pressure on other rocks.

Rock Formation Review

Igneous Rocks Make up 95% of the rocks of the crust of Earth.

Classifications

Intrusive Igneous Rock Forms below the Earth’s surface.

Forms when magma enters a pocket or chamber underground and solidifies into crystals as it cools very slowly.

Slow cooling allows large crystals to form.

Mineral crystals within intrusive igneous rocks are large enough to see without any magnification.

Granite

Extrusive Igneous Rock Forms above the Earth’s surface.

The lava cools very quickly, in less than a day or two, there is no time for elements to bond forming minerals.

Elements are frozen in place. The minerals have enough time to form but not time to grow into large crystals.

PumiceObsidian Scoria

Igneous Rock Review

Textures Glassy Instanteous Cooling No Grains

Textures Aphanitic Quick Cooling Fine Grains

Phaneritic Slow Cooling Course Grain

Mineral Percentage

Lab: Mineral Percentages

Magma Chemistry Felsic Magma is thick and slow moving. Has large amounts of silica (SiO 2 ).

Mafic Magma is hotter, thinner and more fluid. Has lower amounts of silica (SiO 2 ).

Intermediate

Ultramafic Large amounts of iron and magnesium.

Lab: Classifying Igneous Rocks-Interactive

Lab: Classifying Igneous Rocks

Sedimentary Rock Formed by layers of sediments.

Bits of rock, and deposits them on the bottom of the river bed.

Deposited rocks build up in layers, and the weight of the top layers compresses the bottom layers.

The compression squeezes out water, leaving salt crystals that cement the rocks together.

Lab: Sand

Clastic Sedimentary Rock Are composed of pieces of rock, minerals, or fossils that have been cemented together. Sandstone is an example.

Fossils

Chemical Sedimentary Rock Chemical sedimentary rocks form by precipitation or the growth of new minerals in water.

Precipitation can create large sedimentary structures like stalactites and stalagmites, which grow in caves.

Organic Sedimentary Rock

Lab: Classifying Sedimentary Rocks

Metamorphic Rock

Metamorphic Rock Formation

Contact Metamorphism Magma comes in contact with an already existing body of rock.

The existing rocks temperature rises and also becomes infiltrated with fluid from the magma.

Under the intense heat, existing rocks begin to melt and eventually recrystallize as new species that are stable at higher temperatures.

Contact metamorphism produces non-foliated (rocks without any cleavage) rocks such as marble, quartzite, and hornfels.

High Temperature-Low Pressure Metamorphism

Metamorphic Rock Formation Dynamic Metamorphism

Dynamic Metamorphism Dynamic Metamorphism also occurs because of mountain-building.

The mineral grains in rocks subjected to extreme pressure often rearrange themselves in a parallel fashion, creating a foliated texture.

These huge forces of pressure cause the rocks to be bent, folded, crushed, flattened, and sheared.

Contact Metamorphism High Temperature-Low Pressure Metamorphism Dynamic Metamorphism High Pressure-Low Temperature Metamorphism

Metamorphic Rock Formation Regional Metamorphism

Regional Metamorphism The metamorphosed area can cover thousands of square kilometers. Rock in a mountain- building region is transformed by both heat and pressure.

Contact Metamorphism High Temperature-Low Pressure Metamorphism Dynamic Metamorphism High Pressure-Low Temperature Metamorphism Regional Metamorphism Pressure & Temperature Metamorphism

Hydrothermal Metamorphism

Slate Schist Gneiss Sometimes rocks are metamorphosed just a little bit. Other times, rocks are altered intensely.

The degree that rocks are changed by metamorphism depends on how much heat and pressure they are put under, and for how long they are subject to these conditions.

The amount of metamorphism is called the Metamorphic Grade.

Millions of years after a rock has been metamorphosed, geologists can figure out how much heat and pressure it was subject to by looking at its minerals.

Non-Foliates Non-Foliates are metamorphic rocks that have no cleavage at all, do not have wavy layers.

Nonfoliated Textures Hornfils

Foliates Foliates are composed of large amounts of micas and chlorites. These minerals have very distinct cleavage.

Foliated metamorphic rocks will split along cleavage lines that are parallel to the minerals that make up the rock.

Foliated Textures

Slaty Finely crystalline rock in which minerals, such as mica, are aligned paralle to one another, which means that the rock splints readlily along the mica cleavage planes.

Schistose Minerals are aligned in easily visible parallel bands and, because of their platy alignment, the rock splits easily.

Gneissose Characterised by a coarse foliation with individual bands several centimeters across. The foliation may wrap around larger crystals. All the minerals are coarsely granular and readily identifiable.

Phyllitic This texture is formed by the parallel arrangement of platy minerals, usually micas, that are barely macroscopic (visible to the naked eye).

Lab: Metamorphic Rock Classification

Lab: Classifying Metamorphic Rocks

Porphyroblasts Crystals grow quite large surrounding materials remain small.

Lab: Rock Hound