ASBOG Mineralogy and Petrology 2

Question 1

Which crystal system is characterized by three unequal axes, all intersecting at oblique angles?

Accepted Answer

Triclinic

Answer

The triclinic system has three unequal axes (a≠b≠c) with all three axial angles differing from 90°.

Question 2

A rock containing plagioclase, hornblende, and biotite with a porphyritic texture most likely formed as a:

Accepted Answer

Hypabyssal intrusive igneous rock

Answer

Porphyritic texture with those minerals indicates a hypabyssal (shallow intrusive) or volcanic rock where phenocrysts grew slowly before rapid cooling.

Question 3

The mineral sphalerite is the primary ore of which metal?

Accepted Answer

Zinc

Answer

Sphalerite (ZnS) is the principal ore mineral of zinc and commonly occurs with galena in hydrothermal deposits.

Question 4

Which metamorphic index mineral first appears at the lowest grade in Barrow's zones of regional metamorphism?

Accepted Answer

Chlorite

Answer

Chlorite defines the lowest-grade Barrovian zone, appearing before biotite, garnet, staurolite, kyanite, and sillimanite with increasing P-T conditions.

Question 5

Orbicular texture in igneous rocks refers to:

Accepted Answer

Spherical masses of concentric mineralogic shells

Answer

Orbicular texture consists of spheroidal structures with concentric layers of alternating mineral compositions, found in some granites and diorites.

ASBOG - Association of State Boards of Geology Practice Test

ASBOG - Association of State Boards of Geology Practice Test

ASBOG Mineralogy and Petrology 2