igneous textures

Question 1

equigranular texture?

Answer 1

crystals are equally sized (can be coarse, medium or fine)

Question 2

how is fine grained equigranular texture formed?

Answer 2

rapid cooling at the surface are extruded

usually the deeper the larger the crystals (excluding chilled margins)

Question 3

how is vesicular texture formed?

Answer 3

where gas bubbles are trapped in lava as it cools rapidly leaving holes where gas was present

Question 4

vesicular?

Answer 4

rock with ‘holes’ (VESILCLES)

Question 5

what is a vesicle?

Answer 5

holes are called VESICLES are oval and parralel to flow

Question 6

where is vesicular texture found?

Answer 6

at the surface of lava flows where gas rises

basalt + pumice

Question 7

what is amygdaloidal texture?

Answer 7

crystals within vesicles

Question 8

how does amygdaloidal texure form?

Answer 8

vesicular rocks are very porous so groundwater flows through, containing dissolved minerals such as calcium carbonate so calcite will be precipiatated in the holes. can happen millions of years after rock formed

Question 9

what rock is amygdaloidal texture commonly found in

Answer 9

basalt

Question 10

what is an AMYGDALE

Answer 10

an infilled vesicle( crystal in hole)

Question 11

what is a GEODE

Answer 11

partiallu amygdale (crystal not completly filling hole)

Question 12

what rock is amygdaloidal texture commonly found in

Answer 12

basalt

Question 13

what is an AMYGDALE

Answer 13

an infilled vesicle( crystal in hole)

Question 14

what is a GEODE

Answer 14

partially amygdale (crystal not completly filling hole)

Question 15

what is flow banding (texture)

Answer 15

dark aligned minerals aligned parallel to flow direction

Question 16

how does flow banding form in rocks?

Answer 16

layers of dark and light minerals form due to seperation of minerals within a silicic lava flow. usualy seen in rhyolite

Question 17

what is porphyritic texture

Answer 17

crystalline, large and small crystals

Question 18

how does porphyritic texture form?

Answer 18

2 stage cooling process
large crystals (phenocrysts) form first from cooling slowly
surrounded by finer groundmass that cooled quickly

Question 19

how does porhyritic granite form

Answer 19

phenocrysts: often pottasium feldspar form slowly at great depths (around 30km). the magma and feldspar crystals move up with crust by diapiric action to form a batholith ast a deth of around 15km. the rest cools slowly to form the coars grained crystals of the groundmass

Question 20

how does prorphyritic basalt form

Answer 20

phenocrysts: plagioclase feldspar form in magma chamber below volcano, when eruption occurs, plagioclase crystals and magma are erupted to the surface where rapid cooling forms the groundmass (fine grained)