ASBOG Mineralogy and Petrology 4

Question 1

The silica tetrahedron (SiO₄⁴⁻) in olivine group minerals is arranged as:

Accepted Answer

Isolated tetrahedra with no shared oxygens

Answer

Olivine is a nesosilicate (island silicate) where each SiO₄ tetrahedron shares no oxygens with neighboring tetrahedra.

Question 2

Which sedimentary rock, upon contact metamorphism, typically recrystallizes to form marble?

Accepted Answer

Limestone or dolostone

Answer

Limestone and dolostone are carbonate rocks that recrystallize to marble under heat and pressure, coarsening the calcite or dolomite grains.

Question 3

In igneous petrology, the term 'cumulate' refers to rocks formed by:

Accepted Answer

Crystal settling or accumulation from a magma chamber

Answer

Cumulate rocks form when early-crystallizing minerals sink or float in a magma chamber and accumulate into distinct layers.

Question 4

Which mineral group includes muscovite, biotite, and phlogopite?

Accepted Answer

Micas

Answer

Muscovite, biotite, and phlogopite are all sheet silicates belonging to the mica group, characterized by perfect basal cleavage.

Question 5

A granodiorite differs from a true granite primarily in having:

Accepted Answer

More plagioclase than alkali feldspar

Answer

Granodiorite contains more plagioclase than alkali feldspar (P/(A+P) ratio 65–90%), while granite has more alkali feldspar.

ASBOG - Association of State Boards of Geology Practice Test