Rocks and Minerals

Which mineral can scratch plagioclase feldspar?

• amphibole

• calcite

• dolomite

• quartz

Answer explanation

On p. 16 of ESRT, quartz is the only mineral that is harder than plagioclase feldspar listed.

Plagioclase feldspar has a hardness of 6, and quartz has a hardness of 7, so quartz must be able to scratch plagioclase feldspar.

How do sedimentary rocks form?

• heat and/or pressure

• compaction and/or cementation

• melting and solidification

• metamorphism

Answer explanation

On page 6 of ESRT, the only processes that lead to the formation of a sedimentary rock are compaction and/or cementation.

compaction = squeezing sediments together

cementation = gluing them together

Which minerals bubble when a drop of acid is placed on them?

• calcite and dolomite

• muscovite mica and sulfur

• fluorite and olivine

• halite and talc

Answer explanation

For calcite and dolomite, "bubbles with acid" is a distinguishing characteristic listed on ESRT p. 16.

The igneous rock rhyolite consists of potassium feldspar, plagioclase feldspar, biotite, amphibole, and which other mineral?

• garnet

• quartz

• pyroxene

• olivine

Answer explanation

If you draw a line down from the center of the box for rhyolite, the line will cross all minerals listed as well as quartz.

Which metamorphic rock has experienced the most intense heat and pressure?

• schist

• slate

• gneiss

• phyllite

Answer explanation

On ESRT p. 7, the downward arrow indicates INCREASING heat and pressure. Gneiss is listed at the bottom, indicating that it formed from the most intense heat and pressure.

Slate --> Phyllite --> Schist --> Gneiss

(listed in order of increasing heat/pressure)

Quartz sandstone that encounters contact metamorphism would become:

• schist

• quartzite

• phyllite

• slate

Intrusive rocks:

• cool slowly and have large crystals

• cool quickly and have large crystals

• cool slowly and have small crystals

• cool quickly and have small crystals

Answer explanation

Intrusive rocks solidify underground where the temperatures are warmer than the surface.

Because of this, intrusive rocks are able to cool slowly.

The longer the cooling time, the bigger the crystal size.

Which best describes how an igneous rock forms?

• weathering and erosion

• compaction and/or cementation

• melting and solidification

• heat and/or pressure

Which igneous rock is cooled quickly on the surface?

• gabbro

• pumice

• granite

• pegmatite

Answer explanation

Pumice is the only extrusive rock listed.

Extrusive = formed above the surface of the Earth

Because pumice formed above the surface, it cooled very quickly and does not have crystals (non-crystalline).

Which best describes an intrusive igneous rock?

• cools slowly, fine-grained

• cools quickly, fine-grained

• cools quickly, coarse-grained

• cools slowly, coarse-grained