Section 5.1 Flashcards
What are igneous rocks?
Rocks formed from the crystallization of magma.
What is lava?
Magma that flows out onto Earth’s surface.
What is extrusive igneous?
FIne-grained igneous rocks that cool quickly on Earth’s surface.
What are instructive igneous?
Coarse-grained igneous rocks that cool slowly beneath Earth’s surface.
What is the difference between magma and lava?
Lava is magma that cools quickly on Earth’s surface and forms fine-grained igneous rocks such as rhyolite. Magma cools slowly beneath Earth’s surface and forms coarse-grained igneous rocks such as granite.
What is the most common intrusive igneous rock?
Granite
What are the elements that are found in magma?
Oxygen, silicon, aluminum, iron, magnesium, calcium, potassium, and sodium.
What are the factors that affect magma formation?
Temperature: increases with depth in Earth’s crust, known as geothermal gradient.
Pressure: increases with depth, from weight of overlying rock.
Water content: rocks and minerals often contain small amounts of water, as water content increases the melting point decreases.
Mineral content: different minerals have different melting points.
Compare and contrast partial melting and fractional crystallization.
Partial melting- the process whereby some minerals melt at low temperatures while other minerals remain solid. This is why magma is often a slushy mix of crystals and molten rock. As each group of minerals melts, different elements are added to the magma changing its composition.
Fractional crystallization- when magma cools it crystallizes in the reverse order of partial melting. The process wherein different minerals form at different temperatures. Similar to partial melting in that the composition of magma may change. However, during fractional crystallization the changes occur because each group of minerals crystallizes, it removes elements from the remaining magma instead of adding new elements.
What does the Bowen’s reaction series illustrate?
The relationship between cooling magma and mineral formation because as magma cools, kminerals form in predictable patterns. Bowen discovered two main branches of crystallization. The first pattern is characterized by a continuous gradual change of mineral compositions in the feldspar group. The second is characterized by an abrupt change of mineral type in the iron-magnesium group.
Describe the change of composition in the feldspars group.
Undergo a continuous change of composition. As magma cools, the first feldspars to form are rich in calcium. As cooling continues, these feldspars react with magma and their calcium rich compositions change to sodium rich compositions. Sometimes when magma cools rapidly, the calcium rich areas are unable to react completely resulting in zoned crystals with sodium outer layers and calcium cores.
Describe the change of composition in the iron-rich minerals.
Undergo abrupt changes during fractional crystallization. Example, when magma rich in iron and magnesium cools to around 1800 degrees C, olivine begins to crystallize. Olivine continues to form until the temperature drops to 1557 degrees C. A new mineral, pyroxene then begins to form as the previously formed olivine reacts with magma.
What is crystal separation?
Geologists hypothesized that under certain conditions, newly formed crystals are separated from magma and the chemical reactions between the magma and minerals stop. Can occur when crystals settle to the bottom of the magma body and when liquid magma is squeezed from the crystal mush to form two distinct igneous bodies with different compositions.
What is layered intrusion?
In some magma bodies the minerals form into distinct bands. The result is layered intrusion. The settling of crystals, flowing currents in the magma, and temperature gradients within the magma chamber may all play a role. Layered igneous intrusions can be valuable sources of rare metals.
