igneous rocks pt.2

Question 1

2 types of igneous forming minerals

Answer 1

• Mafic minerals = olivine, pyroxene, amphibole
• Felsic minerals = Plagioclase Feldspar, Orthoclase Feldspar, Muscovite Mica

Question 2

what 2 things are Igneous rocks classified based on

Answer 2

1. Composition -> magma source
2. Texture -> cooling history
   Fast cooling—smaller crystals
   Slow cooling—larger crystals

Question 3

4 categories of igneous rocks

Answer 3

Felsic (or silicic) - High Si/O, low Fe/Mg - light grey
Intermediate
Mafic
Ultramafic - low Si/O, high Fe/Mg - dark grey

Question 4

what can be used to estimate chemical composition of igneous rocks

Answer 4

color (gray scale)

Question 5

what is BOWEN’S REACTION SERIES

Answer 5

the order in which minerals crystallize from silicate melt as It cools

Question 6

how does Mineral composition of a rock effect temperature of crystallization

Answer 6

Mafic minerals (rich in Fe / Mg) crystallize at higher temperatures than felsic minerals (low in Fe / Mg)

Question 7

how are igneous rocks named

Answer 7

on the basis of their texture and composition

Question 8

what is texture

Answer 8

the size and arrangement of the minerals

Question 9

what is composition

Answer 9

the assemblage of minerals

Question 10

4 types of igneous rock texture

Answer 10

• Glassy texture
• Vesicular texture
• Pyroclastic texture
• Crystalline texture - Phaneritic texture (coarsely crystalline), Aphanitic texture (finely crystalline), Porphyritic texture (2 distinct grain sizes, large and small)

Question 11

what does the 2 distinct grain sizes of Phaneritic texture indicate

Answer 11

a 2-stage history:
- Initial slow cooling -> large phenocrysts (crystalized at relatively high T)
- Subsequent eruption cooled remaining melt quickly