Rocks: Mineral Mixtures Irish legend claims that the mythical hero Finn MacCool built the Giant’s Causeway, shown here. But this rock formation is the.

Rocks: Mineral Mixtures

Irish legend claims that the mythical hero Finn MacCool built the Giant’s Causeway, shown here. But this rock formation is the result of the cooling of huge amounts of molten rock. As the molten rock cooled, it formed tall pillars separated by cracks called columnar joints

Section 1The Rock CycleScientists define rock as a naturally occurring solid mixture of one or more minerals and organic matter. It may be hard to believe, but rocks are always changing. The continual process by which new rock forms from old rock material is called the rock cycle

The Value of RockRock has been an important natural resource as long as humans have existed. Early humans used rocks as hammers to make other tools. They discovered that they could make arrowheads, spear points, knives, and scrapers by carefully shaping rocks such as chert and obsidian.Rock has also been used for centuries to make buildings, monuments, and roads. Buildings have been made out of granite, limestone, marble, sandstone, slate, and other rocks. Modern buildings also contain concrete and plaster, in which rock is an important ingredient

Processes That Shape the EarthWeathering, Erosion, and DepositionThe process in which water, wind, ice, and heat break down rock is called weathering. Weathering is important because it breaks down rock into fragments. These rock and mineral fragments are the sediment of which much sedimentary rock is made.

The process by which sediment is removed from its source is called erosion . Water, wind, ice, and gravity can erode and move sediments and cause them to collect.

Bryce Canyon, in Utah, is an excellent example of how the processes of weathering and erosion shape the face of our planet

The process in which sediment moved by erosion is dropped and comes to rest is called deposition . Sediment is deposited in bodies of water and other low-lying areas. In those places, sediment may be pressed and cemented together by minerals dissolved in water to form sedimentary rock.

Heat and PressureSedimentary rock made of sediment can also form when buried sediment is squeezed by the weight of overlying layers of sediment. If the temperature and pressure are high enough at the bottom of the sediment, the rock can change into metamorphic rock. In some cases, the rock gets hot enough to melt. This melting creates the magma that eventually cools to form igneous rock.

How the Cycle ContinuesBuried rock is exposed at the Earth’s surface by a combination of uplift and erosion. Uplift is movement within the Earth that causes rocks inside the Earth to be moved to the Earth’s surface. When uplifted rock reaches the Earth’s surface, weathering, erosion, and deposition begin.

Rock ClassificationCompositionThe minerals a rock contains determine the composition of that rockFor example, a rock made of mostly the mineral quartz will have a composition very similar to that of quartz. But a rock made of 50% quartz and 50% feldspar will have a very different composition than quartz does.

TextureThe size, shape, and positions of the grains that make up a rock determine a rock’s texture Sedimentary rock can have a fine-grained, medium-grained, or coarse-grained texture, depending on the size of the grains that make up the rock

The texture of igneous rock can be fine-grained or coarse-grained, depending on how much time magma has to cool. Based on the degree of temperature and pressure a rock is exposed to, metamorphic rock can also have a fine-grained or coarse-grained texture.

Murray Avenue MS255 I Murray Avenue

Huntingdon Valley, PA 19006

Dr. Sid A. MentryMr. Matt O' MorphicSteady State universityVolcanology Department

Your Name

Dear Dr. Sid A Mentry,

Sincerely,

Section 2Igneous Rockigneous comes from a Latin word that means “fire.”

Igneous rock forms when hot, liquid rock, or magma, cools and solidifies. The type of igneous rock that forms depends on the composition of the magma and the amount of time it takes the magma to cool.

Origins of Igneous RockIgneous rock begins as magma. There are three ways magma can form: when rock is heated, when pressure is released, or when rock changes composition

When magma cools enough, it solidifies to form igneous rock. Magma solidifies in much the same way that water freezes.

But there are also differences between the way magma freezes and the way water freezes. One main difference is that water freezes at 0°C. Magma freezes between 700°C and 1,250°C.

Also, liquid magma is a complex mixture containing many melted minerals. Because these minerals have different melting points, some minerals in the magma will freeze or become solid before other minerals do

Composition and Texture of Igneous Rockrocks differ from one another in what they are made of and how fast they cooled.

The light-colored rocks are less dense than the dark-colored rocks are. The light-colored rocks are rich in elements such as aluminum, potassium, silicon, and sodium. These rocks are called felsic rocks. The dark-colored rocks, called mafic rocks, are rich in calcium, iron, and magnesium, and poor in silicon

What happens to magma when it cools at different rates? The longer it takes for the magma or lava to cool, the more time mineral crystals have to grow. The more time the crystals have to grow, the larger the crystals are and the coarser the texture of the resulting igneous rock is.

In contrast, the less time magma takes to cool, the less time crystals have to grow. Therefore, the rock that is formed will be fine grained. Fine-grained igneous rock contains very small crystals, or if the cooling is very rapid, it contains no crystals.

Igneous Rock FormationsIgneous rock formations are located above and below the surface of the Earth. You may be familiar with igneous rock formations that were caused by lava cooling on the Earth’s surface, such as volcanoes. But not all magma reaches the surface. Some magma cools and solidifies deep within the Earth’s crust.

Intrusive Igneous RockWhen magma intrudes, or pushes, into surrounding rock below the Earth’s surface and cools, the rock that forms is called intrusive igneous rock

Intrusive igneous rock usually has a coarse-grained texture because it is well insulated by surrounding rock and cools very slowly. The minerals that form are large, visible crystals.

Masses of intrusive igneous rock are named for their size and shape.

Plutons are large, irregular-shaped intrusive bodies. The largest of all igneous intrusions are batholiths.

Stocks are intrusive bodies that are exposed over smaller areas than batholiths.

Sheetlike intrusions that cut across previous rock units are called dikes, whereas sills are sheetlike intrusions that are oriented parallel to previous rock units.

Extrusive Igneous RockIgneous rock that forms from magma that erupts, or extrudes, onto the Earth’s surface is called extrusive igneous rock Extrusive rock is common around volcanoes. It cools quickly on the surface and contains very small crystals or no crystals

An active lava flow is shown in this photo. When exposed to Earth’s surface conditions, lava quickly cools and solidifies to form a fine-grained igneous rock.

When lava erupts from a volcano, a lava flow forms. Sometimes lava erupts and flows from long cracks in the Earth’s crust called fissures. Lava flows from fissures on the ocean floor at places where tension is causing the ocean floor to be pulled apart. This lava cools to form new ocean floor.

When a large amount of lava flows out of fissures onto land, the lava can cover a large area and form a plain called a lava plateau. Pre-existing landforms are often buried by these lava flows.