GEOL 1303
Name: Huong Nguyen
Homework 2 – Matter, Minerals, and Igneous Rocks
1) What occurs in an atom to produce a positive ion? A negative ion? (2 pts)
An atom would lose its electrons to produce a positive ion.
An atom would add electrons to produce a negative ion.
2) Given its place on the periodic table, what type of ion would Radium (Ra) be? What type of
ion would Bromine (Br) be? (2 pts)
Radium (Ra) = positive ion
Bromine (Br) = negative ion
3) Apart from their difference in color, what is one main distinction between light and dark
silicate minerals? (2 pts)
The light silicate minerals have more potassium and sodium.
The dark silicate minerals have more iron, magnesium, and calcium.
4) What aspect of the arrangement of different chemical bonds in Pyroxene result in the mineral
having two cleavage planes? (2 pts)
Pyroxene has tetrahedral bonds which are strong and single chains stack each other.
5) Using figure 4.5 in your textbook (also in the lecture slides), provide the name for the
following igneous rocks: (1 pt each)
a. A phaneritic rock made mainly of olivine and pyroxene, with lesser amounts of
calcium-rich plagioclase feldspar.
Peridotite
b. An phaneritic rock containing about 50% plagioclase feldspar, about 35% amphibole,
10% pyroxene, and minor amounts of other felsic silicates.
Diorite
c. An phaneritic rock containing about 30% calcium-rich plagioclase feldspar, about
55% pyroxene, and 15% olivine
Gabbro
d. A aphanitic rock containing about 20% quartz, 40% potassium feldspar, 20%
sodium-rich plagioclase feldspar, a few percent muscovite, and the remainder dark
colored silicate.
Rhyolite
6) Name and briefly describe two mechanisms by which mantle rock can melt without an
increase in temperature (4 pts).
Decompression: As rock moves from an area of high pressure to an area of low pressure,
there will be a pressure drop that causes the rock to reach and pass the melting curve.
Wet Melting: Wet melting occurs when water and other volatile components are introduced
to solid rock, producing a low melting point. This mechanism is similar to adding salt to the
ice. This way would decrease the freezing temperature of ice and change it into liquid.
7) At what specific types of plate boundaries do these two melting mechanisms dominantly
occur at respectively? (2 pts)
Divergent boundaries and convergent boundaries.