Metamorphic Rocks Lab

Question 1

What is the difference between a foliated and a non-foliated rock?

Answer 1

Foliated rocks are the ones where you can visibly see the layers inside the rock. Non-foliated means you cannot.

Question 2

Two types of foliation

Answer 2

Large-scale or regional foliation

Question 3

How do you determine the metamorphic grade of a rock?

Answer 3

Increase in crystal size and change in mineralogy (Chlorite -> Biotite/Muscovite -> Garnet -> Kyanite)

Question 4

What are porphyroblasts?

Answer 4

When metamorphic minerals such as garnet and kyanite occur as large crystals within a finer-grained matrix, they are called porphyroblasts

Question 5

Metamorphic rock textures

Answer 5

Crystalline, or remnant-clastic (always specify the grain size if the rock is remnant-clastic)

Question 6

Foliated metamorphic rock types that come from mudstones or shales

Answer 6

Slate, Phyllite, Schist

Question 7

Foliated metamorphic rock that comes from mudstone or felsic igneous rock

Answer 7

Gneiss

Question 8

Slate

Answer 8

Has clean, flat breakage along closely spaced planes. Slates can be confused with shales, but slates are shinier, generally having an egg-shell type sheen.

Question 9

Phyllite

Answer 9

Has very closely parallel planes and a glossy appearance due to the parallel alignment of microscopic mica crystals. Has a satin-type sheen.

Question 10

Schist

Answer 10

Has an approximately parallel arrangement of mica crystals that are large enough to see with the naked eye. To name a schist you must include two of its most abundant minerals in its name

Question 11

Gneiss

Answer 11

Has discrete layers of mineral content giving the rock a banded appearance (gneissic texture). Typically, the dark bands are composed of hornblende and/or biotite, whereas light bands are composed of quartz and feldspar

Question 12

Non-foliated metamorphic rock types

Answer 12

Quartzite, metaconglomerate, marble, amphibolite

Question 13

Quartzite

Answer 13

Comes from a quartz sandstone. Quartz grains will be tightly packed and polygonal.

Question 14

Metaconglomerate

Answer 14

Comes from a conglomerate. Large clasts may still be recognizable, but they will be packed tightly in a very well-cemented matrix. Clasts may also be stretched, flattened, or otherwise deformed.

Question 15

Marble

Answer 15

Come from carbonate rocks (limestone or dolostone). Carbonate minerals that make up the original rock will grow into larger, polygonal carbonate minerals. Fossils and ooids may become unrecognizable due to the extent of deformation during metamorphism

Question 16

Amphibolite

Answer 16

Comes from a mafic igneous rock. The resulting metamorphic rock will be dark-colored due to the abundance of hornblende and plagioclase. These rocks may also contain garnet.