WorksheetsIgneous Rock Textures and Compositions
Total questions: 65
Worksheet time: 46mins
Describes the shape, size, and distribution of mineral grains in a rock. It can also be considered whether a rock has crystals or not (glassy), if it is bubbly (vesicular), etc
Rock textures
Rock compositions
Rock components
Rock appearance
The slower the magma (or lava) cools, the ____ the crystals that are formed grow. This is because the atoms in the melt have more time to migrate through the melt and attach to existing crystals, making them ____ if the cooling process is slow.
(a)
When cooling is rapid, atoms link up with their neighbours and form (a) crystals.
If a melt cools very quickly, ____ crystals will form and the melt will solidify as a glass (which has ____ crystal structure)
(a)
Caused by rapidly cooled magma that cooled at or near the Earth's surface, such as a lave flow.
Phaneritic
Aphanitic
Porphyritic
Pegmatitic
Fine-grained crystals.
Porphyritic
Phaneritic
Aphanitic
Pyroclastic
Example of aphanitic:
Rhyolite
Basalt
Pegmatite
Andasite
Coarse-grained crystals.
Glassy
Aphanitic
Phaneritic
Pegmatitic
Formed from slowly cooled magma deep within the crust such as a magma chamber.
Pegmatitic
Aphanitic
Porphyritic
Phaneritic
Example of phaneritic:
Gabbro
Diorite
Granite
Dolerite
Large crystals (called phenocrysts) in small crystal groundmass.
Porphyritic
Aphanitic
Glassy
Pyroclastic
Formed by a magma that was slowly cooled and started to crystallise phenocrysts, before erupting and then cooling rapidly on the surface.
Pyroclastic
Aphanitic
Porphyritic
Pegmatitic
Example of porphyritic:
Dolerite
Andesite (sometimes)
Porphyritic granite
Diorites (sometimes)
No crystals
Phaneritic
Aphanitic
Pyroclastic
Glassy
Formed when lava is rapidly cooled by air or water
Aphanitic
Glassy
Pyroclastic
Porphyritic
Example of glassy:
Obsidian
Tuff
Basalt
Pegmatite
Not made of crystals, but composed of rock fragments.
Pyroclastic
Aphanitic
Porphyritic
Pegmatitic
The volcanic form of a breccia, when rocks formed during a violent eruption are compacted to form a rock.
Phaneritic
Porphyritic
Glassy
Pyroclastic
Example of pyroclastic:
Tuff
Basalt
Pumice
Obsidian
Very coarse crystals
Porphyritic
Pyroclastic
Pegmatitic
Aphanitic
The last part of a magma to crystallise is fluid rich, and will form pegmatites, which often contain rare minerals and ore.
Pegmatitic
Porphyritic
Pyroclastic
Phaneritic
Example of pegmatitic:
Dolerite
Gabbro
Obsidian
Pegmatite
Aphanitic has:
no crystals
fine-grained crystals
coarse-grained crystals
very coarse crystals
Phaneritic has:
Very coarse crystals
Composed of rock fragments
Large crystals (phenocrysts) in small crystal groundmass
Coarse-grained crystals
Porphyritic has:
Large crystals (phenocrysts) in small crystal groundmass
Fine-grained crystals
No crystals
Composed of rock fragments
Glassy has:
Fine-grained crystals
Composed of rock fragments
Very coarse crystals
No crystals
Pyroclastic has:
Coarse-grained crystals
Composed of rock fragments
Large crystals (phenocrysts) in small crystal groundmass
Very coarse crystals
Pegmatitic has:
Very coarse crystals
No crystals
Large crystals (phenocrysts) in small crystal groundmass
Fine-grained crystals
(a) are the last rock to form from a cooling magma chamber.
As a magma chamber cools, lots of common elements are removed. ____ is concentrated in the last part of the melt. The ____ry melt contains all of the elements that were 'incompatible' with the mineral being formed. Many of these are rare and valuable.
(a)
When an erupting rock contains significant amount of carbon dioxide, it will form a ____ rock. ____ are the bubbles left in the rock by the gas.
(a)
Sometimes, a magma or lava will pick up chunks of other rocks surrounding it. These are called ____ (rocks from elsewhere). An excellent example of a ____ is a peridotite. This rock makes up most of the upper mantle, but only ever makes it to the earth's surface when it becomes trapped in erupting magma.
(a)
Classify Basalt:
Aphanitic, extrusive, mafic
Porphyritic, extrusive, felsic
Phaneritic, intrusive, mafic
Pegmatitic, intrusive, felsic
Classify Andesite:
Pyroclastic, extrusive, felsic
Aphanitic, extrusive, intermediate
Porphyritic, extrusive, intermediate
Phaneritic, intrusive, mafic
Classify Pegmatite:
Aphanitic, extrusive, mafic
Aphanitic, intrusive, felsic
Phaneritic, extrusive, felsic
Pegmatitic, intrusive, felsic
Classify Tuff:
Porphyritic, intrusive, intermediate
Pyroclastic, explosive extrusive, felsic
Phaneritic, intrusive, felsic
Glassy, extrusive, intermediate
Classify dolerite:
Phaneritic, intrusive, mafic
Porphyritic, intrusive / extrusive, mafic
Pyroclastic, intrusive, mafic
Aphanitic, extrusive, mafic
Classify diorite:
Aphanitic, extrusive, felsic
Phaneritic, extrusive, mafic
Phaneritic, intrusive, intermediate
Porphyritic, intrusive, intermediate
Classify Granite:
Aphanitic, extrusive, mafic
Phaneritic, intrusive, felsic
Porphyritic, intrusive, felsic
Pyroclastic, extrusive, mafic
Classify Obsidian:
Glassy, extrusive, felsic
Glassy, extrusive, mafic
Pyroclastic, intrusive, felsic
Aphanitic, extrusive, intermediate
Classify Gabbro:
Phaneritic, intrusive, mafic
Aphanitic, intrusive, felsic
Porphyritic, extrusive, intermediate
Pyroclastic, extrusive, mafic
Classify Rhyolite:
Porphyritic, extrusive, mafic
Phaneritic, intrusive, mafic
Aphanitic, extrusive, felsic
Aphanitic, intrusive, intermediate
Classify Pumice:
Porphyritic, intrusive, mafic
Aphanitic, extrusive explosive, felsic
Phaneritic, extrusive, felsic
Pyroclastic, extrusive explosive, felsic
Composition of igneous rocks refers to the (a) components that make up the rock. Knowing, and being able to describe what a rock is made of is a useful way to figure out how it was created.
The term mafic comes from the term ferromagnesian and these rocks are (a) in iron and magnesium.
The term (a) comes from the abundance of feldspars and silicon which make up these rocks
As minerals crystallise, they may sink and remove components from the melt. This is called ____ ____.
(a)
In fractional crystallisation, the first mineral to crystallise removes iron and magnesium, leaving the melt more (a) .
The oceanic crust is dominated by (a) rocks. They are formed at mid-ocean ridges, hot-spots (plumes), and in rift valleys, which are all examples of decompression melting.
Intermediate rocks do not contain (a) , but do contain pyroxenes and plagioclase feldspars. They have less Fe and Mn than mafic rocks.
Intermediate rocks form at ocean-ocean collision zones where subduction occurs, and are the chief components of ____ ____.
(a)
Felsic rocks do not contain olivine or pyroxenes and are composed of mainly amphiboles, micas, (a) , and quartz. They are low in Fe and Mn
Felsic rocks make up most of the (a) crust and are formed at oceanic-continental subduction zones.
What mineral is removed from intermediate rocks?
Magnesium
Olivine
Pyroxenes
Feldspars
What minerals are removed from felsic rocks?
Olivine
Pyroxene
Peridotite
Silicon
Where are mafic rocks formed?
Hot-spots
Continental subduction zone
Mid-ocean ridges
Plumes
Where are intermediate rocks formed?
Hot-spots
Island arcs
Continental subduction zones
Ocean to ocean subduction zones
Where are felsic rocks formed?
Oceanic subduction zones
Continent to ocean subduction zones
Hot-spots
Island arcs
Which rocks form in batholith structures?
Granite
Diorite
Gabbro
Andesite
Which rocks form in stock structures?
Rhyolite
Granite
Gabbro
Diorite
Which rocks form in sill structures?
Granite
Dolerite
Andesite
Rhyolite
Which rocks form in lava capped plateau structures?
Andesite
Rhyolite
Diorite
Basalt
Which rocks form in dike structures?
Andesite
Rhyolite
Dolerite
Diorite
Which rocks form in laccolith structures?
Pegmatite
Granite
Diorite
Gabbro
Which rocks form in volcanic structures?
Rhyolite
Tuff
Obsidian
Pumice
Basalt
