Geology for Engineers
Assessment 1 Answers
Year 2026
0027 68 628 1800
,
,
,
,
,
,
, QUESTION 1
1.1
The discontinuous branch of Bowen’s reaction series shows minerals crystallising from
high temperatures (~1300 °C) to low temperatures (~750 °C), where olivine forms first
at the highest melting point, followed sequentially by pyroxene, amphibole, and biotite
as each mineral reacts with the cooling melt to form a new structure. This progression
corresponds to magma types: basaltic (mafic, ~45–52% silica) at high temperatures,
andesitic (intermediate, ~52–63% silica) at mid-range, and rhyolitic (felsic, ~63–75%
silica) at low temperatures. The associated intrusive (coarse-grained) rocks are
gabbro (mafic), diorite (intermediate), and granite (felsic), while their extrusive (fine-
grained) equivalents are basalt, andesite, and rhyolite respectively. Across the series,
there is a clear colour progression from dark (green/black, mafic) to light (grey/pink,
felsic) as temperature decreases and silica content increases.
Assessment 1 Answers
Year 2026
0027 68 628 1800
,
,
,
,
,
,
, QUESTION 1
1.1
The discontinuous branch of Bowen’s reaction series shows minerals crystallising from
high temperatures (~1300 °C) to low temperatures (~750 °C), where olivine forms first
at the highest melting point, followed sequentially by pyroxene, amphibole, and biotite
as each mineral reacts with the cooling melt to form a new structure. This progression
corresponds to magma types: basaltic (mafic, ~45–52% silica) at high temperatures,
andesitic (intermediate, ~52–63% silica) at mid-range, and rhyolitic (felsic, ~63–75%
silica) at low temperatures. The associated intrusive (coarse-grained) rocks are
gabbro (mafic), diorite (intermediate), and granite (felsic), while their extrusive (fine-
grained) equivalents are basalt, andesite, and rhyolite respectively. Across the series,
there is a clear colour progression from dark (green/black, mafic) to light (grey/pink,
felsic) as temperature decreases and silica content increases.
