Homework#3:Weathering
Name:
This homework helps you understand chemical weathering of rocks (which you must remember are made up of one or
more minerals). You do NOT need to write a balanced chemical reaction, but you DO need to identify each reactant and
product and note whether it’s dissolved (aq) or solid (s). You can use FeO/OH to represent the group of oxide and
hydroxide minerals containing Fe. I’ve done the first one for you so you know what you are expected to do.
Rock #1: Gabbro, a mafic igneous rock
This particular gabbro contains two minerals: Plagioclase feldspar (Na,Ca)2[Al2Si2]O8 and Pyroxene Ca(Fe,Mg)Si2O6
Write down all the chemical weathering reactions that occur in this rock. If a mineral is inert (i.e., doesn’t react), then
just write that.
Reaction of plagioclase feldspar:
(Na,Ca)2[Al2Si2]O8 + H2O + CO2 → Na+(aq) + Ca2+(aq) + H4siO4(aq) + Clay(s)
Reaction of pyroxene:
Ca(Fe,Mg)Si2O6 + H2O + CO2 → Ca2+(aq) + Mg2+(aq) + H4SiO4(aq) + FeO/OH(s)
Solid clasts of what mineral(s) are produced/remain when granite weathers?
FeO/OH + Clay
Rock #1: Dolostone (10 pts)
Write down all the chemical weathering reactions that occur in this rock. If a mineral is inert (i.e., doesn’t react), then
just write that.
Rock #2: Quartz sandstone (5 pts)
Write down all the chemical weathering reactions that occur in this rock. If a mineral is inert (i.e., doesn’t react), then
just write that.
Rock #3: Andesite, an intermediate volcanic igneous rock (15 pts)
This particular andesite contains three minerals with the following formulas: Plagioclase feldspar (Na,Ca)2[Al2Si2]O8,
Amphibole Ca(Mg,Fe,Al)5[AlSi7] O22(OH)2, and Magnetite (Fe3O4).
Write down all the chemical weathering reactions that occur in this rock. If a mineral is inert (i.e., doesn’t react), then
just write that.
Solid clasts of what mineral(s) are produced/remain when andesite weathers? (5 pts)
Rock #3: Carbonatite, a rare igneous rock (20 pts)
This particular carbonatite contains four minerals: Dolomite, Magnetite Fe3O4, Fluorite CaF2, and Muscovite
KAl2[AlSi3]O10(OH)2
Write down all the chemical weathering reactions that occur in this rock. If a mineral is inert (i.e., doesn’t react), then
just write that.
Solid clasts of what mineral(s) are produced/remain when carbonatite weathers? (5 pts)