Francis, 2013
Introductory Petrology EPSC 212: 2013 Mid-Term
1. The following diagram is an imaginary liquidus projection with the compositions of
the stable mineral phases indicated by black dots with normal bold letters and the
corresponding liquidus fields for each mineral phase indicated by the italicized bold
letters. Determine the nature (eutectic versus peritectic) of the 4 ternary invariant
points (1, 2, 3, & 4) and indicate the down temperature directions on each of the
univariant curves on the diagram using a " > ". Indicate which of the latter are
reaction curves, by labeling them with a " >> " rather than the " > " for cotectics.
Identify the invariant points (1 through 4) corresponding to the first liquids formed
during partial melting of each of the 5 circled solid compositions within the
diagram: U, W, X, Y, & Z. Show all work directly on the diagram.
Francis, 2013
Introductory Petrology EPSC 212: 2013 Mid-Term – cont.
2. The liquidus projection below is a repeat of the one on the previous page. In this
case, assume that the 5 circled compositions are liquids (U, W, X, Y, & Z) within
the diagram. For each liquid composition, trace the liquid line of descent with
decreasing temperature if it were to undergo perfect fractional crystallization. Draw
the liquid lines of descent directly on the diagram, and briefly describe them in the
exam booklet, indicating in each case the invariant point at which the last liquid
crystallizes.
Francis, 2013
3. Give the exact chemical formula for each of the following minerals:
diopside
forsterite
albite
orthoclase
muscovite
tremolite
enstatite
anorthite
nepheline
ilmenite
4. Describe and contrast the factors controlling the solubility of SiO2 and CaCO3. Go on to
describe the differences in the degree of saturation of ocean water with respect to
dissolved SiO2 and CaCO3. Discuss the reasons for these differences and their
implications for the origin of chert and limestone, with specific reference to precipitation
mechanisms and mineralogical changes during diagenesis.