26. Most volcanoes are located on or near plate boundaries.  Give an example of a volcano that is not on a plate boundary and describe a hypothesis that can explain it.
 
The Hawaiian islands are in the middle of the Pacific plate.  They formed by hot spot volcanism.  An anomalously hot region in the lower mantle generates some partial melt.  The melt rises to the surface because it is buoyant generating a series of volcanoes over time as the Pacific plate moves over the stationary hot spot.
 
27. You are given two clear crystals.  One is Calcite and one is Quartz.  Describe two separate methods that you could use to distinguish between them.
 
Test 1 — Acid test.  Calcite will fizz when treated with HCL.  Quartz does not.
Test 2 — Hardness.  Calcite is soft, Quartz is much harder.  So Quartz will scratch Calcite but not vice versa.
Test 3 — Cleavage.  Calcite cleaves parallel to its crystal faces.  Quartz does not have cleavage.  It fractures along a curved surface.
Other possible tests — Crystal Habit, Density
 
28. The Palisades Sill in New York State is an example of fractional crystallization.  Describe the distribution of minerals within the sill and how that distribution was created.
 
The Palisades sill is layered vertically.  The top and bottom are chill zones that consist of basalt.  In between the slower cooling magma produced olivine at the bottom, Na rich feldspar at the top and pyroxene and Ca rich feldspar in the middle.  This layering was generated by fractional crystallization.  As the magma initially cooled the first mineral to crystallize out was olivine.  These crystals settled to the bottom.  Next to crystallize out were pyroxene and Ca-rich feldspar.  These crystals settled on top of the olivine.  Finally, the remaining magma crystallized out as Na-rich feldspar.
 
29. Sketch/describe the internal compositional layers of the Earth.
 
From Top (Surface) to Bottom
 
Crust — 4 to 70 km thick outer layer made up of Silicates.  Mostly Silica rich, Fe, Mg poor
 
Mantle — 2900 km thick middle layer made up of Fe, Mg rich silicates
 
Core — Fe and Ni composition, about 3000 km in radius.  Inner part is solid, outer part is liquid.
 
30. What is the principle of uniformitarianism?  Give a specific example of its application.
 
Processes that we see today (e.g., river erosion, transport, and deposition) have occurred in the same fashion throughout Earth’s history although the rates may have varied.  Examples of this are the Colorado river producing the Grand Canyon over geologic time rather than the canyon being produced by some unknown, catastrophic process or the Wilson cycle creating supercontinents which then break up and reassemble.
 
31. A sandstone is composed mostly of smooth grains of quartz that are all the same size.  What process(es) formed this sedimentary rock.
 
The processes that produce clastic sedimentary rocks are: weathering, erosion, transportation, deposition, burial, compaction and cementation.  A well-sorted, well rounded, quartz sandstone also implies that these grains were transported a long distance by rivers or wind and deposited in a sand rich environment such as a desert or beach.
 
32. Using the rock cycle, trace the path from magma to igneous rock to sedimentary rock to a metamorphic rock.  Include the plate tectonic environment in which each rock forms.
  
At a continental convergent boundary, melting of the subducting oceanic lithosphere plus sediments creates a magma which rises to the surface because of buoyancy.  The magma is erupted from a volcano and forms an igneous rock.  Once at the surface the igneous rock is broken down by weathering and transported to the edge of the continent where it is deposited, buried and converted into a sedimentary rock.  As the ocean basin closes the sedimentary rock is thrust upwards during mountain building and subjected to high temperature and pressure which converts it into a metamorphic rock.
 
33. Sketch/describe how Silicon and Oxygen in silicate minerals share electrons
 
The basic building block of silicate minerals is the tetrahedra of one Silicon +4 ion and four Oxygen minus 2 ions ionic bonded together.  This leaves the tetrahedra with a net negative charge of minus 4.  This net change must be balanced either by adding more positively charged ions (e.g., Ca+2 or Fe+2) or by sharing Oxygen between tetrahedra by creating chains, sheets, or frameworks. 
 
34. What process(es) determines the size of crystals in igneous rocks?
 
The primary process that determines crystal size is cooling time.  If the magma cools below ground it cools slowly and the crystals grow large.  If the magma is erupted to the surface, it cools quickly and only small crystals form.
 
35. What evidence did Wegener use to support his theory of continental drift?  Why did his theory not gain wide acceptance?
 
Evidence — Edges of continents fit together like a jigsaw puzzle, structures/rocks also line up when continents are put back together (e.g., Appalachian Mountains and the Highlands of Scotland), some fossils are only found in limited areas of now widely separated continents, paleoclimate evidence for continental glacier on India, S. America, and Australia.
 
Wegener’s hypothesis did not gain wide acceptance because he could not explain what force or process moved the continents thousands of kilometers.