AS Metamorphic Rocks

Question 1

Isochemical

Answer 1

means that no elements are added or removed.

Question 2

Granoblastic

Answer 2

the texture found in metamorphic rocks that contain interlocking equidimensional crystals.

Question 3

Foliation

Answer 3

the texture found in metamorphic rocks, formed by the preferred alignment of flat, platy minerals.

Question 4

Slaty cleavage

Answer 4

the texture in fine grained rocks formed by low grade regional metamorphism. Platy minerals recrystallise perpendicular to the direction of stress applied during metamorphism so that the rock splits into thin sheets.

Question 5

Cataclasis

Answer 5

the brittle fracturing and grinding down of existing rock, usually in fault zones.

Question 6

Porphyroblasts

Answer 6

large crystals that have grown during recrystallisation in a metamorphic rock and surrounded by a finer grained groundmass of other crystals.

Question 7

Schistosity

Answer 7

the texture in medium and coarse grained metamorphic rocks formed by the preferred alignment of flat/tabular minerals. The alignment is perpendicular to the direction of stress applied during metamorphism. No traces of original bedding remain.

Question 8

Gneissose banding

Answer 8

the segregation of light- and dark-coloured minerals into layers or bands at the scale of mm to cm in thickness. The light band is normally granoblastic (granular) and the dark band normally shows schistosity.

Question 9

Metamorphic grade

Answer 9

a measure of the intensity of metamorphism. Although increases in temperature only result in increasing grade in contact metamorphism, grade is also used to describe regional metamorphism where both temperature and pressure vary.

Question 10

Country rock

Answer 10

the rock into which an igneous rock has been intruded.

Question 11

Metamorphic aureole

Answer 11

a region surrounding an igneous intrusion in which the country rocks have been recrystallised and changed by heat from the intrusion.

Question 12

Spotted rock

Answer 12

formed by low grade metamorphism in the outer part of the metamorphic aureole.

Question 13

Index minerals

Answer 13

metamorphic minerals, which are stable under specific temperature and pressure conditions. They indicate the metamorphic grade.

Question 14

Regional Metamorphism

Answer 14

Large scale, convergent plate margins, low to high pressure and low to high temperature. Pressure is significant. Causes foliation

Question 15

Contact Metamorphism

Answer 15

Small scale. Occurs close to igneous intrusions. Temperature high, Pressure low. Forms baked margins and metamorphic aureoles.

Question 16

Dynamic Metamorphism

Answer 16

Occurs at fault zones due to shear stress. Rock fractures- crushed and ground as well as recrystallisation

Question 17

Slate

Answer 17

Parent rock shale. low grade regional metamorphism. Foliation. Slaty cleavage.

Question 18

Phyllite

Answer 18

Parent rock slate. low grade regional metamorphism. Wavy foliation.

Question 19

Schist

Answer 19

Parent rock phyllite. medium grade regional metamorphism. Coarse. Schistosity. Porphyroblasts (garnet).

Question 20

Gneiss

Answer 20

Parent rock schist. High grade regional metamorphism. Coarse. Gneissose banding

Question 21

Marble

Answer 21

Parent rock limestone. Contact or Regional metamorphism. Granoblastic.

Question 22

Metaquartzite

Answer 22

Parent rock sandstone. Contact or Regional metamorphism. Granoblastic.

Question 23

Spotted rock

Answer 23

Parent rock slate, contact metamorphism

Question 24

low grade metamorphic index mineral

Answer 24

chlorite

Question 25

medium grade metamorphic index mineral

Answer 25

garnet

Question 26

high grade metamorphic index mineral

Answer 26

sillimanite