igneous rocks: born of fire. general characteristics of magma igneous rocks form as molten rock...
Post on 15-Jan-2016
229 views
TRANSCRIPT
![Page 1: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/1.jpg)
Igneous Rocks:Born of Fire
![Page 2: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/2.jpg)
General characteristics of magma
• Igneous rocks form as molten rock cools and solidifies (Ignis = fire)
• General characteristics of magma• Parent material of igneous rocks• Forms from partial melting of rocks• Magma at surface is called lava
![Page 3: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/3.jpg)
General characteristics of magma
• General characteristic of magma• Rocks formed from lava = extrusive, or
volcanic rocks• Rocks formed from magma at depth =
intrusive, or plutonic rocks
![Page 4: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/4.jpg)
General characteristics of magma
• The nature of magma• Consists of three components:– Liquid portion = melt
– Solids, if any, are silicate minerals
– Volatiles = dissolved gases in the melt, including water vapor (H2O), carbon dioxide (CO2), and sulfur dioxide (SO2)
![Page 5: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/5.jpg)
General characteristics of magma
• Crystallization of magma• Cooling of magma results in the
systematic arrangement of ions into orderly patterns• The silicate minerals resulting from
crystallization form in a predictable order• Texture - size and arrangement of mineral
grains
![Page 6: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/6.jpg)
Igneous textures
• Texture is used to describe the overall appearance of a rock based on the size, shape, and arrangement of interlocking minerals
![Page 7: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/7.jpg)
Igneous textures
• Factors affecting crystal size
1. Rate of cooling– Slow rate = fewer but larger crystals
– Fast rate = many small crystals
– Very fast rate forms glass
2. % of silica (SiO2) present
3. Presence of Dissolved gases
![Page 8: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/8.jpg)
Igneous textures
• Types of igneous textures• 1. Aphanitic (fine-grained) texture– Rapid rate of cooling
–Microscopic crystals
–May contain vesicles (holes from gas bubbles)
• 2. Phaneritic (coarse-grained) texture– Slow cooling
– Large, visible crystals
![Page 9: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/9.jpg)
Aphanitic texture
Figure 4.3 A
![Page 10: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/10.jpg)
Phaneritic texture
Figure 4.3 B
![Page 11: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/11.jpg)
![Page 12: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/12.jpg)
Igneous textures
• 3. Porphyritic texture–Minerals form at different temperatures
– Large crystals (phenocrysts) are embedded in a matrix of smaller crystals (groundmass)
• 4. Glassy texture– Very rapid cooling of lava
– Resulting rock is called obsidian
![Page 13: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/13.jpg)
Andesite
Figure 4.13
![Page 14: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/14.jpg)
Porphyritic texture
![Page 15: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/15.jpg)
Porphyritic texture
Figure 4.3 C
![Page 16: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/16.jpg)
Glassy texture
Figure 4.3 D
![Page 17: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/17.jpg)
Igneous textures
• Types of igneous textures• 5. Pyroclastic texture
– Fragmental appearance produced by violent volcanic eruptions
– Often appear more similar to sedimentary rocks
• 6. Pegmatitic texture– Exceptionally coarse
grained– Form in late stages of
crystallization of granitic magmas
![Page 18: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/18.jpg)
Igneous compositions
• Igneous rocks are composed primarily of silicate minerals
• Dark (or ferromagnesian) silicates (Fe, Mg)– Olivine, pyroxene, amphibole, and biotite mica
– These make up “mafic” rocks
• Light (or nonferromagnesian) silicates (Ca, Na, K, higher SiO2)– Quartz, muscovite mica, and feldspars
– These make up “felsic” rocks
![Page 19: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/19.jpg)
Igneous compositions
• Granitic versus basaltic compositions• Granitic composition– Light-colored silicates (color matters!)
– Termed felsic (feldspar and silica) in composition
– High amounts of silica (SiO2)
– Lower density than mafic rocks
–Major constituent of continental crust
![Page 20: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/20.jpg)
Igneous compositions
• Granitic versus basaltic compositions• Basaltic composition– Dark silicates and calcium-rich feldspar
– Termed mafic (magnesium and ferrum, for iron) in composition
– Higher density than felsic (granitic) rocks
– Comprise the ocean floor and many volcanic islands
![Page 21: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/21.jpg)
Igneous compositions
• Other compositional groups• Intermediate (or andesitic) composition
– Contain 25% or more dark silicate minerals– Associated with explosive volcanic activity– Named for Andes mountains
• Ultramafic composition– Rare (on surface) composition that is high in magnesium
and iron– Composed entirely of ferromagnesian silicates– Olivine, Pyroxene
– Mantle rock, sometimes brought to surface by volcanism in
xenoliths
![Page 22: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/22.jpg)
Igneous compositions
• Silica content as an indicator of composition• Exhibits a considerable range in the crust– 45% to 70%
• Silica content influences magma behavior• Granitic magmas = high silica content and
viscous • Basaltic magmas = much lower silica content
and more fluid-like behavior
![Page 23: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/23.jpg)
![Page 24: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/24.jpg)
Igneous compositions
• Naming igneous rocks – granitic rocks• Granite– Phaneritic
– Over 25% quartz, about 65% or more feldspar
– Very abundant - often associated with mountain building
– The term granite includes a wide range of mineral compositions
![Page 25: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/25.jpg)
Granite
Figure 4.9 A
![Page 26: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/26.jpg)
Igneous compositions
• Naming igneous rocks – granitic rocks• Rhyolite– Extrusive COMPOSITIONAL equivalent of
granite
–May contain glass fragments and vesicles
– Aphanitic texture
– Less common and less voluminous than granite
![Page 27: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/27.jpg)
Rhyolite
Figure 4.9 B
![Page 28: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/28.jpg)
![Page 29: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/29.jpg)
![Page 30: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/30.jpg)
Welded tuff (fragments) and obsidian (volcanic glass) in layers
![Page 31: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/31.jpg)
How is Magma formed?
• Melting by heat within the earth
• Decompression melting
• Addition of volatiles
![Page 32: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/32.jpg)
Origin of magma
• Highly debated topic
• Generating magma from solid rock• Role of heat– Temperature increases in the upper crust
(geothermal gradient) average between 20oC to 30oC per kilometer
– Rocks in the lower crust and upper mantle are near their melting points
– Any additional heat may induce melting
![Page 33: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/33.jpg)
Figure 4.18
![Page 34: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/34.jpg)
TEMPERATURE is plotted against PRESSURE (which can be translated to DEPTH in the Earth). The field of the diagram is further subdivided in 9 regions showing the relative temperature and pressure conditions in each field. Note the temperature increases to the right and pressure increases downward.
GEOTHERM (i.e. the increase in temperature with depth in the Earth). The slope of the GEOTHERM is called the GEOTHERMAL GRADIENT (which is the CHANGE IN TEMPERATURE PER KILOMETER). Note that the geothermal gradient is very large between the surface and 100 km depth. Below 100 km, the geothermal gradient is only about 1oC per kilometer.
![Page 35: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/35.jpg)
Origin of magma
• Role of Heat– Convection circulates heat in the mantle– Heated material is less dense and rises– Mantle may partially melt
• Role of pressure– Increases in confining pressure cause an increase in a rock’s
melting temperature – When confining pressures drop, decompression melting occurs
• Role of volatiles– Volatiles (primarily water) cause rocks to melt at lower
temperatures– Important factor where oceanic lithosphere descends into the
mantle
![Page 36: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/36.jpg)
Figure 4.19
![Page 37: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/37.jpg)
Decompression melting
Figure 4.20
![Page 38: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/38.jpg)
Subduction ZoneVolcanism
Plate Boundary
![Page 39: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/39.jpg)
Evolution of magmasWhy is there a DIVERSITY OF
IGNEOUS ROCKS• A single volcano may extrude lavas
exhibiting very different compositions
• Bowen’s reaction series • Minerals crystallize in a systematic fashion
based on their melting points• During crystallization, the composition of the
liquid portion of the magma continually changes (“evolves”) so different minerals will crystallize
![Page 40: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/40.jpg)
Bowen’s reaction series
Figure 4.23
![Page 41: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/41.jpg)
Evolution of magmas
• Processes responsible for changing a magma’s composition
• Magmatic differentiation– Separation of a melt from earlier formed crystals– The Parent Magma minus crystals = new magma
composition
• Assimilation– Changing a magma’s composition by the
incorporation of surrounding rock bodies into a magma
![Page 42: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/42.jpg)
Evolution of magmas
• Processes responsible for changing a magma’s composition
• Magma mixing– Two chemically distinct magmas may produce a
composition quite different from either original magma
![Page 43: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/43.jpg)
Assimilation, magma mixing, and magmatic differentiation
Figure 4.25
![Page 44: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/44.jpg)
Evolution of magmas
• Partial melting and magma formation• Incomplete melting of rocks is known as
partial melting• Formation of basaltic magmas–Most originate from partial melting of ultramafic
rock in the mantle at oceanic ridges
– Large outpourings of basaltic magma are common at Earth’s surface
– These mafic magmas imply a large % of melt at high temperatures
![Page 45: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/45.jpg)
Evolution of magmas
• Partial melting and magma formation• Formation of andesitic magmas–May be produced by interaction of basaltic
magmas and more silica-rich rocks in the crust
–May also evolve by magmatic differentiation
– And incorporation of volatiles into the magma
![Page 46: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/46.jpg)
Evolution of magmas
• Partial melting and magma formation• Formation of granitic magmas–Most likely form as the end product of
crystallization of andesitic magma ???
– Granitic magmas are more viscous than other magmas so they tend to lose their mobility before reaching the surface
– Tend to produce large plutonic structures
![Page 47: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/47.jpg)
![Page 48: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/48.jpg)
Igneous compositions
• Naming igneous rocks – intermediate rocks• Andesite (named after?)– Volcanic origin
– Aphanitic texture
• Diorite– Plutonic CHEMICAL equivalent of andesite
– Coarse grained
![Page 49: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/49.jpg)
Andesite
Figure 4.13
![Page 50: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/50.jpg)
Diorite
Figure 4.14
![Page 51: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/51.jpg)
Igneous compositions
• Naming igneous rocks – basaltic rocks• Basalt– Volcanic origin
– Aphanitic texture
– Composed mainly of pyroxene and calcium-rich plagioclase feldspar
–Most common extrusive igneous rock
![Page 52: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/52.jpg)
Basalt
Figure 4.15 A
![Page 53: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/53.jpg)
Igneous compositions
• Naming igneous rocks – mafic rocks• Gabbro– Intrusive compositional equivalent of basalt
– Phaneritic texture consisting of pyroxene and calcium-rich plagioclase
– Significant % of the oceanic crust
![Page 54: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/54.jpg)
Gabbro
Figure 4.15 B
![Page 55: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/55.jpg)
Igneous compositions
• Naming igneous rocks – pyroclastic rocks• Composed of fragments ejected during a
volcanic eruption• Hot particles weld together then cool• Varieties– Tuff = ash-sized fragments
– Volcanic breccia = particles larger than ash
![Page 56: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/56.jpg)
Igneous compositions
• Naming igneous rocks – granitic rocks• Obsidian– Dark colored
– Glassy texture
• Pumice– Volcanic
– Glassy texture
– Frothy appearance with numerous voids
![Page 57: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/57.jpg)
Igneous RocksIdentification Scheme
![Page 58: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/58.jpg)
![Page 59: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/59.jpg)
![Page 60: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/60.jpg)
Classification and nomenclature of plutonic rocks according to their modal mineral contents using theQAPF diagram (based on Streckeisen, 1976, Fig. 1a).The corners of the double triangle are Q = quartz, A = alkali feldspar, P = plagioclase and F = feldpathoid. However, for more definitions refer to section B.2. This diagram must not be used for rocks in which mafic mineral content, M, is greater than 90%.
![Page 61: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/61.jpg)
![Page 62: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/62.jpg)
Intrusive plutonic rocks
Extrusive volcanic rocks
![Page 63: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/63.jpg)
![Page 64: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/64.jpg)
![Page 65: Igneous Rocks: Born of Fire. General characteristics of magma Igneous rocks form as molten rock cools and solidifies (Ignis = fire) General characteristics](https://reader036.vdocument.in/reader036/viewer/2022062322/56649d595503460f94a38b72/html5/thumbnails/65.jpg)
International Union of the Geologic Sciences (modified)Classification of igneous rocks