Igneous

Question 1

Andesite

Answer 1

Fine grained intermediate extrusive rock
Main minerals are plag and hornblende
Common in subduction zone volcanoes
Volcanic equivalent of Diorite
Named for Andes mountains

Question 2

Anorthosite

Answer 2

Felsic intrusive rock
Main mineral is plag (90-100%)
Named for high levels of Anorthite

Question 3

Aplite

Answer 3

Fine grained felsic intrusive rock
Can have composition of granite but is much finer grained (sugary texture, more of a textural name)
Forms in narrow cracks where heat loss to adjacent rocks is quick and crystals don’t have time to grow

Question 4

Basalt

Answer 4

Fine grained mafic extrusive rock
Volcanic equivalent of Gabbro and Diabase
Low Silica (45-50%)
Main minerals are pyroxene (augite), calcic plag and olivine

Question 5

Carbonatite

Answer 5

Composed of at least 50% carbonate minerals
Can be intrusive or extrusive
Associated with alkaline igneous rocks
Associated with continental rift tectonic settings
Host of apatite, REEs and niobium

Question 6

Dacite

Answer 6

Fine grained felsic extrusive rock
Intermediate composition between Andesite and Ryolite
Volcanic equivalent of Granodiorite
Main minerals are plag, with biotite, hornblende and pyroxene

Question 7

Diabase

Answer 7

Medium grained mafic subvolcanic rock
Texturally in between Gabbro and Basalt (same composition)
Occurs in shallow intrusions

Question 8

Diorite

Answer 8

Coarse grained intermediate intrusive rock
Plutonic equivalent of Andesite
Main minerals are Na rich plag and hornblende
Occurs from partial melting of mafic rock above a subduction zone

Question 9

Dunite

Answer 9

Coarse grained ultramafic plutonic rock
Main Mineral is Olivine (>90%)
Common in the mantle but rare at surface

Question 10

Gabbro

Answer 10

Coarse grained mafic intrusive rock
Main minerals are Ca-rich plag, pyroxene
Plutonic equivalent of Basalt and Diabase

Question 11

Granite

Answer 11

Coarse grained felsic intrusive rock
Differs from Granodiorite because at least 35% of the feldspar must be alkali feldspar rather than plag
Plutonic equivalent of Rhyolite

Question 12

Granodiorite

Answer 12

Coarse grained intermediate-felsic intrusive rock
Contains more quartz than Diorite
Main minerals are plag
Plutonic equivalent of Dacite
Biotite and amphiboles are more common in Granodiorite than they are in Granite

Question 13

Ignimbrite

Answer 13

Pyroclastic flow deposit rock

Contain Pumice, Scoria, Lapilli and Ash

Question 14

Kimberlite

Answer 14

Ultramafic rock containing olivine and one or more of pholgopite, serpentine, diopside, monticellite, calcite

Question 15

Monzonite

Answer 15

Plutonic rock with intermediate composition between Syenite and Diorite
Equal amounts k-spar and plag
Little or no quartz