Mineralogy and Petrology Flashcards

Which property best distinguishes dolomite from calcite in the field?

Answer: Dolomite fizzes weakly only in powdered form with cold HCl

Dolomite reacts sluggishly with cold dilute HCl only when powdered, whereas calcite fizzes vigorously with cold acid even in massive form.

In the IUGS classification of plutonic rocks, a rock with 60% plagioclase, 30% pyroxene, and 10% olivine would be classified as:

Answer: Norite or gabbro

A rock with that mafic mineral content (pyroxene + olivine) and calcic plagioclase plots in the gabbro/norite field of the QAPF diagram.

The characteristic luster of metallic sulfides like pyrite and chalcopyrite is called:

Answer: Metallic luster

Metallic luster describes the shiny, opaque reflective quality of sulfide minerals that resembles polished metal.

Eclogite is a high-pressure metamorphic rock primarily composed of:

Answer: Omphacite pyroxene and pyrope-rich garnet

Eclogite is defined by the assemblage of omphacite (Na-Al pyroxene) and pyrope-rich garnet, forming under very high pressures in subduction zones.

Which igneous rock texture describes a fine-grained groundmass with no visible crystals?

Answer: Aphanitic

Aphanitic texture occurs when magma cools rapidly, producing crystals too small to see with the naked eye.

The term 'foliation' in metamorphic rocks refers to:

Answer: Planar fabric defined by aligned platy minerals or compositional layering

Foliation is the planar structural fabric in metamorphic rocks created by preferred orientation of platy minerals like mica or by compositional banding.

Pseudomorphism occurs when:

Answer: One mineral replaces another while retaining the original crystal shape

A pseudomorph retains the external form of an original mineral while the internal composition has been replaced by a different mineral.