18-Geol-A1 Mineralogy and Petrology · May 2017
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
EGBC National Exam — Geological Engineering, 04-Geol-A1 Mineralogy and Petrology, 2017-May. Closed book; no calculator permitted. Part 1 requires all five 10-mark short-answer questions (50 marks); Part 2 lists eight questions with instructions to answer "5 of the 7" (a source discrepancy noted on the exam page itself).
Reference texts: Klein & Dutrow, Manual of Mineral Science, 23rd ed. (silicate structural classification, mineral chemistry/formulas); Winter, Principles of Igneous and Metamorphic Petrology, 2nd ed. (magmatic differentiation and mixing, metamorphic agents/facies, volcanic processes, phase equilibria and AFM projections, magma viscosity, layered intrusions, tectonic melting mechanisms).
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
Regional metamorphism is metamorphism affecting large volumes of crust (tens to hundreds of km²), driven by the combined action of elevated heat, elevated confining pressure and significant differential stress, typically in orogenic (mountain-building) belts at convergent plate boundaries. Unlike contact metamorphism, differential stress from active tectonic deformation is always present, which is what produces its defining textural signature.
Foliation intensifies with increasing grade: slate (slaty cleavage, sub-microscopic) → phyllite (phyllitic sheen from sub-mm mica) → schist (schistosity, macroscopic visible mica/amphibole alignment) → gneiss (gneissic banding, compositional segregation into felsic and mafic layers). Lineation, crenulation cleavage and porphyroblasts (e.g. garnet) are also common.
For a pelitic protolith, a classic Barrovian index-mineral sequence records progressively increasing grade along successive isograds:
| Zone | Index mineral |
|---|---|
| Lowest grade | Chlorite |
| Biotite | |
| Garnet | |
| Staurolite | |
| Kyanite | |
| Highest grade | Sillimanite |
This mineral/textural progression is the standard field and petrographic signature used to map metamorphic grade across an orogenic belt.
