3.1.1. State whether the following sentences are t (true) or f (false), according to the information from the text

1. Metamorphic rocks compose about 25% of the continental crust.

2. Metamorphic rocks are a combination of sedimentary and igneous rocks altered under pressure and heat conditions.

3. There are two main metamorphic processes.

4. Mechanical deformation includes grinding and crushing of the country rock.

5. Pre-existing mineral assemblages are chemically recrystallized by changes in the temperature, pressure or chemical milieu.

6. All metamorphic rocks show a combination of both mechanical deformation and chemical reaction.

7. Metamorphic rocks show contrasts because of the differences in original rock chemistry or change.

8. Mechanical deformation forms the so-called cataclastic rocks.

9. Contact metamorphic rocks are formed by a great increase in heat without differential stress.

10. Contact metamorphic rocks are found in zones surrounding sedimentary rocks on the surface of the crust.

11. Regional metamorphic rocks are a result of both deformation and mineral reaction.

12. Foliation and lineation are characteristic features of various rock motions in the process of recrystallization.

Match the definition with the following terms.

1. regional metamorphic rocks	a. metamorphic rocks in which particles are reduced to a small size
2. cataclasis	b. developed on a regional scale in response to both deformation and mineral reaction
3. recrystallization	c. readjustment of the material
4. cataclastic rock	d. formed by a significant increase in temperature in the absence of differential stress
5. contact metamorphic rocks	f. preexisting mineral assemblages are destabilized by changes in the temperature, pressure or chemical milieu

3.2 Informative reading: Metamorphic rocks

Read the following text and fill in the chart after the text.

The third category is rock that has been changed. The minerals in an igneous rock, or the particles in a sedimentary rock, may look fairly permanent, but in certain circumstances (under extreme conditions of pressure or temperature) they can change and recrystallize into something new. The new rock product is called a metamorphic rock.

There are two types of metamorphic rock. The first is regional metamorphic rock in which the altering force is one of pressure rather than of temperature. These are found deep within the interior of mountain chains and are believed to constitute the lower parts of the crust. Different degrees of pressure produce different grades of metamorphic rock. Slight pressure will produce a low-grade metamorphic rock, in which the only difference will be that the minerals will have been realigned in a different direction. Often this produces flat crystals of mica that are orientated perpendicular to the direction of the applied pressure. The result is a rock that has planes of weakness running in one direction and which can split easily into flat slabs. Slate and phyllite are typical low-grade metamorphic rocks. On the other hand, intense pressure will completely change the mineralogical makeup of the rock and produce a high-grade metamorphic rock. The chemical components may recrystallize into a totally different set of minerals from the original rock and the new minerals may form in distinct bands, often crumpled and contorted as evidence of the great pressures involved. Gneiss is the typical high-grade metamorphic rock showing distinct banding.

A typical sequence of rocks – from unconsolidated sediment, through sedimentary rock, through different grades of metamorphic rock, depending on the depth in the crust at which different conditions are found:

SURFACE – Mud (sediment)

Mudstone (sedimentary rock)

3 miles (5 km) deep

Shale

6 miles (10 km) deep

Slate (low-grade metamorphic rock) Different kinds of micas develop

9 miles (15 km) deep

Schist (medium-grade metamorphic rock)

12 miles (20 km) deep

Gneiss (high-grade metamorphic rock)

15.5 miles (25 km)

Migmatite (ultrametamorphic rock)