Igneous Rocks

Question 1

What are the two categories an Igneous Rock can fall under?

Answer 1

Intrusive and Extrusive

Question 2

What are extrusive rocks?

Answer 2

• formed above ground
• lava
• pyroclastic material (Explody volcano bits)
• fine grained
• Cools quickly

Question 3

What are intrusive rocks?

Answer 3

• formed underground

- large crystals (phenocrysts)

Question 4

What is a Mafic rock?

Answer 4

• made up of minerals (dark)
• iron and mg
• basalt (extrusive)
• gabbro (intrusive)

Question 5

What is a Felsic rock?

Answer 5

• made up of aluminum silicates (light)
• lighter colours
• rhyolite (extrusive)
• granite (intrusive)

Question 6

What is a dike?

Answer 6

When magma moves up through a rock vertically/at an angle and cross cuts. Doesn’t make it to the surface

Question 7

What is a Sill?

Answer 7

magma intrudes and moves along the surface of a rock. (Flat)

Question 8

What is a stock?

Answer 8

makes it all the way up to the volcano and gets extruded.

Question 9

What is a pyroclastic?

Answer 9

explosive material from a volcano

Question 10

What is country rock?

Answer 10

Sedimentary rock that has been intruded.

Question 11

What is a vein

Answer 11

Contains gold, platinum, ect.

Question 12

What is lava called before it makes it to the surface?

Answer 12

Magma

Question 13

What is a Flood Basalt?

Answer 13

Result of a giant volcanic eruption. It is made of basalt and is a huge contributor to mass extinction

Question 14

Mafic Magma

Answer 14

-more runny

Question 15

Silica rich magma

Answer 15

• more explosive
• viscous
• more pyroclastic material

Question 16

What are the two ways extrusives can come out of a volcano?

Answer 16

• lava
• pyroclastics (the size of the rock itself.)
  
  • eg; volcanic ash vs volcanic bomb

Question 17

What is porphyry

Answer 17

• course grains forming slowly under the earth.

- erupts quickly.

Question 18

What is a Felsic rock mostly made up of?

Answer 18

• Orthoclase Feldspar
• Quartz
• Plagioclase feldspar
• Muscovite

Question 19

What is a Mafic rock mostly made up of?

Answer 19

• Pyroxene
• Olivine
• Some plagioclase

Question 20

Mafic Lavas

Answer 20

• high Fe/Mg and low silica content (dark in colour),
• they erupt at 1000-1200oC, and
• highly fluid (can travel at speeds of 100 km/hr).
• Basaltic

Question 21

Intermediate Lavas

Answer 21

-andesitic
-they have an intermediate composition
between basalt and rhyolite.
-intrusions of intermediate magma form diorite

Question 22

Rhyolitic Lavas

Answer 22

-low Fe/Mg and high silica content,
-they erupt at 800-1000oC,
-highly viscous (they travel 10 times slower than basalt),
because of its viscosity, it resists flow
-the vesicular variety of rhyolite is called “pumice”.

Question 23

How do magmas form?

Answer 23

• Magmas start out felsic and become mafic by melting rocks above it.
• Subducting rock partially melts since the minerals melt at different temperatures.

Question 24

What are the two main ways of changing magmas composition?

Answer 24

1. Subduction which causes magma to move up.

2. Melting rocks around it.

Question 25

Xenoliths

Answer 25

country rock that has melted into the magma.

Question 26

What is decompressional melting?

Answer 26

Mantle (up) pressure (down). This causes solid rock to melt without the introduction of additional heat.

Question 27

What is magmatic differentiation?

Answer 27

• when different minerals crystallize at different temperatures
• composition of the parent magma changes from its initial ultramafic composition