GS 106 - Introduction to Physical Geology

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16) Choose four properties that all minerals have and describe what they are and how they are identified in a mineral.

Answer: There are actually 7 to choose from really:

1) Crystal habit: This is the shape a crystal grows at the atomic level if it is able to freely grow. Most mineral samples don’t have a crystal habit, bit if it did you would just look at the shape of the crystal.

2) Cleavage: This is the tendency of a mineral to break along a plane of weakness in the crystalline lattice. You can identify this in the mineral by looking at whether the mineral breaks in a repetitive fashion or you can look for a surface on a mineral that has a flash or sheen to the surface as well. If a mineral does not have cleavage, it is said to have fracture, and the mineral will shatter chaotically, like glass.

3) Hardness: This is how hard the mineral is structurally based on its bonding in its crystalline lattice and is measures with Moh’s hardness scale. We can find the hardness of a mineral by comparing it to the hardness of an everyday implement like glass or a penny.

4) Specific Gravity: This is basically the density of a mineral relative to an equal amount of water. The easiest way to find the specific gravity is comparing the weight of two minerals to find which one is heaviest.

5) Color: Color is usually determined by the elements present in the composition of a mineral. It can be identified though observation; however, impurities in a mineral can change its color and so its best to use color in conjunction with other minerals.

6) Streak: This is the color of the mineral in its powdered form, which can be different than its visible color because more light is accessing greater surface area of the mineral. Streak is identified by rubbing a mineral sample on a porcelain plate to see the true color.

7) Luster: This is the way mineral samples transmit light. You can identify this through observation and describing the overall look of the mineral with words like metallic, glassy, earthy, etc.

17) Describe the two types of igneous rocks and give an example for each.

Answer: The first type of igneous rock is intrusive igneous rock, which are rocks that cool slowly under ground and have coarse-grained texture. An example of an intrusive igneous rock is Granite (also Diorite, Gabbro, Peridotite, and Dunite). The second type of igneous rock is extrusive igneous rock, which are rocks that cool quickly on the surface of the Earth. An example of an extrusive rock is Rhyolite (also Andesite, Basalt, Pumice, Scoria, and Obsidian)

18) Describe both regional and contact metamorphism and give a general example (not an exact place on Earth) where these types of metamorphism are happening.

Answer: Regional metamorphism is the type of metamorphism that is associated with crustal movements of tectonic plates and is associated with higher heats and pressures. This could happen where tectonic plates are colliding like subduction zones or along continental convergence. Contact metamorphism is associated with high temperatures and low pressures, usually around lava flows, magma chambers or other igneous intrusions.

19) Name and describe the three types of volcanoes. Lastly name a volcano in Oregon and tell me the type of volcano.

Answer: The first type of volcano is a shield volcano, which is a broad, domed volcano with gently sloping sides, characteristic of the eruption of fluid, basaltic lava. The second type of volcano is a composite, or stratovolcano, which s a conical volcano built up by many layers (strata) of hardened lava, tephra, pumice, and volcanic ash. The third type of volcano is a cinder cone, which is a vent by fragments of lava thrown out during eruptions, usually scoria. Hood, Crater Lake, Jefferson, The South Sister and Middle Sister are all composite cones. Newberry and the North Sister are shield volcanoes. Lava Butte and Pilot Butte are cinder cones.

20) Describe both clastic and chemical sedimentary rocks and give an example of both.

Answer: Clastic rocks are rocks composed predominantly of broken pieces or clasts of older weathered and eroded rocks. An example of a clastic rock is shale (or sandstone, breccia, conglomerate, arkose, and claystone). A chemical sedimentary rock is a rock that has mineral crystals made from elements that are dissolved in water (or a solution) that then evaporates. An example of a chemical sedimentary rock  is limestone, gypsum rock, rock salt, and dolomite).

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16) What are the 5 characteristics necessary for a material to be considered a mineral? For the following 3 substances tell me why it isn’t a mineral: glass, wood, and plastic.

Answer: A mineral is solid, naturally occurring, inorganic, has a distinct composition, and contains a crystalline lattice. Glass doesn’t have a crystalline lattice. Wood is organic. Plastic is man-made.

17) Describe the two textures of metamorphic rocks and give an example for each.

Answer: The first texture of metamorphic rocks is foliated and these rocks have a layered texture that looks like a deck of cards. An example of a foliated metamorphic rock is Slate (also Amphibolite, Phyllite, Schist, and Gneiss). The second texture of a metamorphic rock is nonfoliated and these rocks have a more massive look with no layering to them. An example of a nonfoliated metamorphic rock is Marble (also Quartzite, Serpentinite, and Hornfels).

18) Describe the two types of weathering and give an example of both types of weathering.

Answer: The two types of weathering are mechanical and chemical. Mechanical weathering doesn’t change the composition of the rock, it only breaks the rock being weathered into smaller pieces. An example of mechanical weathering is freeze-thaw (or frost-wedging, unloading, pressure-release fracturing, abrasion, thermal expansion or contraction, organic activity, or biogenic). Chemical weathering occurs when a rock is broken down and becomes a different composition than what it started as. An example of chemical weathering is dissolution (or hydrolysis, salt cracking, and oxidation).

19) Describe the 3 ways magma is formed and name a place where magma actively forming in the United States.

Answer: Magma is created in subduction zones by the subducting plate bringing water into the mantle and lowering the minerals melting points that are present. Magma can also be created when tectonic plates are pulled apart and pressure is released on the mantle causing the rock to melt. The last way to make magma is by adding additional heat to the mantle overcoming the pressure of overlying rock, creating magma, and this occurs at hot spots. A place in the United States where magma is actively being produced is underneath the Cascade Volcanic Arc (also in Hawaii, in Yellowstone, and along the Aleutian Volcanic Arc).

20) Describe the two general types of geologic dating and give an example of each.

Answer: The first type of geologic dating is absolute dating, which is defined as the process of determining an approximate computed age in geology through radiometric dating. An example of absolute dating is carbon-14 dating (also potassium 40, Uranium 238, 235, and 232, and Rubidium 87). The other type of geologic dating is relative dating, which is defined as determining the relative order of past events, without necessarily determining their absolute age based on several principles. Examples of relative dating are the principles of original horizontality (also superposition, crosscutting, faunal succession, lateral continuity, inclusion, and also the use of unconformities, sometimes the use of these are called correlation).