silica content of igneous rocks

Question 1

Which igneous rocks have a silica content of more than 66%?

Answer 1

obsidian, pumice rhyolite, granite

Question 2

Which igneous rocks have a silica content of 52-66%?

Answer 2

andesite, diorite

Question 3

Which igneous rocks have a silica content of 45-52%?

Answer 3

basalt, dolerite, gabbro

Question 4

Which igneous rock has a silica content of less than 45%?

Answer 4

peridotite

Question 5

Which igneous rock has a glassy crystal size and is volcanic extrusive?

Answer 5

obsidian

Question 6

Which igneous rocks have a fine crystals size of more than 1mm and are volcanic extrusive?

Answer 6

pumice rhyolite, andesite, basalt

Question 7

Which igneous rock has a medium crystal size of 1-5mm and is a hypabyssal minor intrusion?

Answer 7

dolerite

Question 8

Which igneous rocks have coarse crystals of more than 5mm and are a plutonic major intrusion?

Answer 8

Granite, gabbro, peridotite

Question 9

What igneous rock is between silicic and intermediate?

Answer 9

granodiorite

Question 10

What minerals are silicic? 5

Answer 10

quartz, potassium feldspar, Na plagioclase feldspar, biotite mica, muscovite mica

Question 11

What minerals are intermediate? 5

Answer 11

quartz (rare), potassium feldspar, plagioclase feldspar, biotite mica, hornblende

Question 12

What minerals are mafic? 3

Answer 12

Ca plagioclase feldspar, augite, olivine

Question 13

What minerals are ultramafic? 2

Answer 13

Augite, olivine

Question 14

Explain the difference between the percentage of quartz and silica in a rock

Answer 14

Silica % is not the same as the mineral quartz. Quartz is made from silica, but the silica % includes the silica in all the rock forming minerals. A rock with no quartz will still contain silica in silicate minerals such as olivine