Geology Exam 2 Beyer

-What is partial melting? -What composition does most magma erupt as? -If most magma at the Earth's surface begins as mafic magma derived from melting mantle rock, how do different magma compositions exist/erupt from volcanoes? -In other words, if we start with the same mantle rock and melt it down, why in some locations do we see mafic magma, and in other locations we observe more intermediate/felsic magmas?

* -the point at which rock melts - -

-How do minerals form? Think water, magma, and biological processes. -Are shells made of Calcite considered minerals? If so, does this interfere with the 'generally inorganic' mineral definition?

* -water solutions that contain dissolved minerals -yes, it is not living material but is secreted from living organisms

What are the silicate minerals? What does every silicate mineral contain? What is the silicon-oxygen tetrahedron? What can the Si-O tetrahedron do with one another? (look at the slide with the various silicate structures)

- have silicon and oxygen - light silicates: muscovite, quartz, feldspar -dark silicates: olivine, pyroxene, amphibole, biotite -all silicon minerals have this , they link together and share oxygens

Types of lava flows a. Aa - b. Pahoehoe - c. Block - d. Pillow -

-Aa:mafic lava that cooled quickly, has a chunky appearance -Pahoehoe: mafic lava that has a smooth, often braided appearance, cooled slowly -Block: characteristic of felsic/intermediate lavas, chunky appearance -Pillows: bulbous structures from (commonly) mafic magma erupting on the seafloor

Parts of a volcano - cone, vent, crater, parasitic cone, conduit, magma chamber, pyroclastic materials, lava flows

-Cone: hill formed around the vent -vent: opening at summit -crater: broader depression around the vent -conduit: pipe from magma chamber -chamber: stores magma - pyroclastic materials: things expelled during eruption -lava flows: flowing lava after an eruption

-Igneous compositions - felsic, intermediate, mafic, ultramafic - how do they differ? -What are some rock examples for each composition? -Where would we likely find rocks of each composition?

-Felsic: light silicates, common rocks, highest silica content (ex. granite, obsidian, rhyolite, pumice) -Intermediate: less silica, found in subduction zones, (ex. andesite, diorite) -Mafic: less silica than inter., found in mafic magma and oceans (ex. basalt, gabbro) -Ultramafic: lowest silica value, found in the mantle (ex. peridotite, pyroxenite)

What do we mean when referring to "rock-forming" minerals? What do most of these minerals contain? In other words, what are the two most common elements in the Earth's crust?

-Felspar and Quartz

-Where do igneous rocks come from (what is an igneous parent rock and how will it be related to the resultant igneous rock)? -What is the difference between magma/lava? -Is lava simply liquid rock, or are there other components?

-Igneous rocks are formed by the cooling and hardening of magma. - Magma is composed of molten rock and is stored in the crust. - Lava is magma that comes through the surface of the Earth through a volcano. -

-Bowen's Reaction Series - why is Bowen's work important? -Which minerals will crystallize first from magma? -Which minerals will crystallize last? Think back to light vs. dark silicates - which of these groups was more "silica-rich"? -In other words, the amount of silica in the minerals controls crystallization order (and the melting order if we observe rock melting rather than crystallizing from magma).

-It explains the order of mineral formation and the melting points -Dark Silicates crystalize first, then light silicates

-What does mineral texture refer to? -What terms do we use to describe texture? -What are the cooling histories for the different igneous textures and in which environments would we find these textures? Note terms like intrusive and extrusive.

-It refers to the feel of the rock - Aphanitic: extrusive, fast cool -Phanteritic: intrusive, slow cool -Vesicular: extrusive, fast cool -Glassy: extrusive, fast cool -Porphyritic: extrusive and intrusive, fast cool -Pyroclastic: extrusive, fast cool

What sorts of volcanic hazards exist? (these mainly occur at Composite/Stratovolcanoes)

-Pyroclastic flows -Lahars: mud/debris flow -air quality low, cooler climate

Quiescent v. Explosive eruptions - reasonably, which composition of magma should we expect for each? What do we call the debris generated during an explosive volcanic eruption?

-Quiescent: low viscosity, calm eruptions -Explosive: high viscosity, catastrophic eruptions -pyroclastic flow

Shield volcanoes v. Cinder cones v. Composite/Stratovolcanoes a. Profiles (shapes) of the volcanoes - what do we see for each? How can we explain the profiles based on the eruptions, types of lava, etc.? b. In general, where would we likely find each volcano? c. What style of eruption is common for each volcano? d. Relative (to one another) size of the volcanoes? e. What is each volcano made from? f. What composition of magma/lava should we find at each volcano? Do all volcanoes have extensive lava flows?

-Shield Volcano: large, broad and wide in Hawaii, quiescent eruptions, fluid mafic lava -Cinder Cones: Mexico, rocky debris, steeper than shields, lose debris, hotspots, lava flow is rare from main vent -Stratovolcano/Composite Volcano: enormous eruptions, basic volanco, mt st helens, felsic to intermediate

How do the various magmatic differentiation processes (assimilation, magma mixing, crystal settling) affect a magma's composition over time? Hint: use Bowen's Reaction Series here

-assimilation: incorporated and melting of rocks into magma of rocks into magma changes the composition -magma mixing: 2 independent compositions may rise and form together in a plume of magma -crystal settling: when minerals form they settle out and rest and the composition changes slowly

Mineral diagnostic properties: a. Color - why is color unreliable on its own? Why might any one mineral come in multiple color varieties? b. Streak c. Hardness - Moh's Scale - how do we use it? Minerals with higher hardness values tend to be made of tightly-packed atoms that are strongly bonded. d. Cleavage vs. Fracture - can a mineral exhibit both cleavage and fracture? What does cleavage represent? e. Crystal Shape/(sometimes referred to as 'Crystal Habit') - in nature, why is it rare to find minerals exhibiting their true crystal forms/habits? f. Luster

-controlled by composition, color is unreliable because minerals come in a variety of colors -color of the powder -resistance to scratching, scaled used to determine relative hardness -cleavage: how the mineral prefers to break -fracture: random break -most of these crystals are in tight spaces -shininess of minerals in light

-What causes a volcano to erupt? What are the driving forces? Think dissolved gas within the magma - what does it want to do? (gasses are often referred to as "volatiles" - commonly water, carbon dioxide, various sulfur-based gasses, etc.). What about the density of magma compared to the surrounding solid rock within the Earth - how does this affect the movement of magma?

-increased pressure -*

What is an igneous intrusion? What are some examples of intrusions?

-intrusions formed by crystalized magma -dikes: light, magma cuts across the rock layers and cools -sills: dark, move in between rock layers and cools -batholiths: erosion occurs, deeply buried rocks are exposed at the surface -laccoliths: large intrusions that cool close the the surface and earth buckles around it

Which silicate minerals tend to be more silica-rich? What are the two most common minerals of the Earth's continental crust? What's the most common mineral in any type of crust?

-light silicates -feldspar and quartz -*

What does mineral crystallization mean? How do intrusive/extrusive environments affect crystallization and mineral texture?

-molten rock cooled down and crystalized -Intrusive Rocks are coarse grain and have large mineral crystals -Extrusive have small mineral crystals

What is a caldera and how does it form? These generally exist for the big volcanoes (shield and stratovolcanoes). What might happen to the caldera, and the crustal rock below, if another eruption is imminent?

-partially empty magma chamber, with rocks sitting on top, volcano collapses on itself -the caldera surfaces and resurges back up

What is viscosity? How does the viscosity of a mafic magma compare to that of felsic magma? Why are they different (what controls viscosity)? **this expands on question 1

-resistance to flow -felsic lava is more viscous because of silica

Prediction of volcanic eruptions is tough - and usually not as accurate as we would like. Regardless, what conditions could you monitor at a volcano that may suggest a volcanic eruption is imminent? What is the "resting" state v. "active" state of a volcano?

-seismic activity -resting: can erupt but are currently not -active: currently erupting

What are mineral polymorphs? Example from the notes

-share compositions but have different characteristics like crystalline structures (graphite and diamonds)

-What is a unit cell? -What happens to our mineral's properties if we observe the mineral on a scale smaller than one unit cell worth of atoms?

-smallest number of atoms that represent a crystal -*

-Is the Earth's mantle solid or liquid? -What is the geothermal gradient? -If the Earth's mantle is largely solid, how does melting occur within this layer? i.e. decompression melting, subduction zones

-solid rock -the melting curve of rocks -decompression melting occurs when pressure if dropped and they can melt easier along with the water component of subduction zones

Light vs. dark silicates - why are these groups different? What do the dark silicates contain that the light silicates lack? Which minerals have higher densities? In which rocks do we find more light silicates? Dark silicates?

-they have different silicon levels -light silicates lack iron and magnesium -dark silicates have higher density

Despite their minor abundance in the Earth's crust, what important purpose do many of the non-silicate minerals serve?

-they serve as oceanic crust

Which mineral class is commonly observed in igneous rocks?

Felsic, Intermediate, Mafic, Ultramafic

____ controls viscosity

composition

As temperature goes up, viscosity goes _____

down

the more water vapor in the magma, the ____ viscosity

less

What are the 5 criteria a substance must meet to be considered a mineral? Be able to explain what each means.

substance must be solid, generally inorganic, naturally occurring, crystalline structure, defined chemical composition (chemical formula)

What are minerals made of?

unit cells: smallest number of atoms that represent a mineral

As silica content goes up, viscosity goes ____

up