focuses on the composition and texture of igneous rocks (rocks such as granite or basalt which have crystallized from molten rock or magma). Igneous rocks include volcanic and plutonic rocks.
5
New cards
Sedimentary petrology
focuses on the composition and texture of sedimentary rocks
6
New cards
Metamorphic petrology
focuses on the composition and texture of metamorphic rocks
7
New cards
Texture
refers to the mutual relationship of the different mineralogical constituents in a rock
8
New cards
refers to the large scale features or field characteristics of the rocks
Types of Textures: difference in their relative grain size
21
New cards
Directive
Types of Textures: exhibit perfect or semi perfect parallelism of crystals or crystallites in the direction of the flow of magma
22
New cards
Intergrowth
Types of Textures: two or more minerals may crystallize out simultaneously in a limited space so that the resulting crystals are mixed up or intergrown
23
New cards
Intergranular
Types of Textures: specifically termed intersertal if the material filling the spaces is glassy in nature
24
New cards
Flow structures
Structures of Igneous rocks due to mobility of magma/lava: development of parallel or nearly parallel layers or bands or streaks in the body of an igneous roc
25
New cards
Pillow structures
Structures of Igneous rocks due to mobility of magma/lava: development of bulbous, overlapping, pillow like surfaces in the body of igneous mass
26
New cards
Ropy and blocky lava
Structures of Igneous rocks due to mobility of magma/lava: surfaces show broken and fragmented appearance, these are called the blocky lava
27
New cards
Spherulitic structures
Structures of Igneous rocks due to mobility of magma/lava: distinguished by the presence of thin mineral fibers of various sizes arranged in perfect or semi perfect radial manner about a common centre
28
New cards
Orbicular structures
Structures of Igneous rocks due to mobility of magma/lava: rare type of structure of igneous rocks, rock mass appears as if composed of ball like aggregations
Structures due to cooling of magma: development of cracks or joints in the rocks formed from these sources, these joints sometimes follow definite patterns
33
New cards
Rift and grain
Structures due to cooling of magma: indicate two separate directions, often used by quarry men, in which the igneous rocks like granite can be broken from the main rock body with a comparative ease. The equally spaced joints are producing cubical blocks.
34
New cards
Vesicular structure
Structures due to cooling of magma: escape of gases while cooling is going on leads commonly to the formation of cavities of various sizes and shapes in the cooled mass.
35
New cards
Miarolitic structure
Structures due to cooling of magma: sometimes small and distinct cavities are formed during the crystallization of magma, these cavities often containing projecting crystals are called miarolitic cavities.
36
New cards
1. Reaction structure 2. Xenolithic structure
Miscellaneous Structure
37
New cards
Reaction structure
Miscellaneous Structure: characterized by the presence in the rock of some incompletely altered minerals conspicuously surrounded on their borders by their alteration products, often happens that some earlier formed minerals react with the magma during the subsequent stages of crystallization
38
New cards
Xenolithic structure
Miscellaneous Structure: imposed on the igneous rocks because of incorporation of foreign material, the foreign fragments are termed xenoliths
39
New cards
1. Concordant 2. Discordant
Forms of igneous rocks has two types:
40
New cards
1. Sills 2. Phacoliths 3. Lopoliths 4. Laccoliths
Concordant Bodies
41
New cards
Sills
igneous intrusions that have been injected along or between the bedding planes or sedimentary sequence are known
42
New cards
Phacoliths
small sized intrusives that occupy positions in the troughs and crests of bends called folds
43
New cards
Lopoliths
igneous intrusions, which are associated with structural basins, that are sedimentary beds inclined towards a common centre
44
New cards
Laccoliths
concordant intrusions due to which the invaded strata have been arched up or deformed into a dome
45
New cards
1. Dykes/dikes 2. Volcanic necks 3. Batholiths
Discordant Bodies
46
New cards
Dykes/dikes
defined as columnar bodies of igneous rocks that cut across the bedding plane or unconformities or cleavage planes and similar structures
47
New cards
Volcanic necks
in some cases vents of quiet volcanoes have become sealed with the intrusions, such congealed intrusions
48
New cards
Batholiths
these are huge bodies of igneous masses that show both concordant and discordant relations with the country rock
49
New cards
Sedimentary petrology
the classification and study of sedimentary deposits/rocks. This study is the basis for understanding sediment transport and deposition processes, as well as shedding light on the environmental setting where the sediments were formed.
50
New cards
Sedimentary rocks
formed by the accumulation, compaction and consolidation of sediments
51
New cards
secondary rocks
They are {1}, derived from the sediments produced by the weathering of pre-existing rocks
52
New cards
Water
The accumulation and compaction of these sediments usually take place in the presence of {1}
53
New cards
1. Nature of gathering ground 2. Duration of transport 3. Mixing up of sediments 4. Allogenic and authigenic minerals
Factors influencing mineralogical composition:
54
New cards
1. Origin of grains 2. Size of grains 3. Shapes of grains 4. Packing of grains 5. Fabric of grains 6. Crystallization trend
Described in terms of orientation of longer axes of grains
60
New cards
Crystalline granular amorphous textures
Crystallization trend
61
New cards
Grain size
It is a good indicator of the energy or force required to move a grain of a given size
62
New cards
Smaller grain sizes
generally indicate greater transport distances and duration
63
New cards
Sorting
It will generally improve with the constant or persistent moving of particles, and thus can indicate if particles were transported over a long distance or for a long time period.
64
New cards
Sorting
indicate selective transport of a particular grain size.
65
New cards
Rounding
a good indicator for the amount of abrasion experienced by sediments.
66
New cards
Mechanical Structures Chemical Structures Organic Structures
form by alteration or modification of any kind of preexisting rock.
74
New cards
Metamorphism
may be caused by pressure, heat, or by water or other fluids or gases that infiltrate a protolith.
75
New cards
process of metamorphism
can involve changes in the minerals present, changes in rock texture, or changes in rock composition, or any combination of the three.
76
New cards
Ortho-metamorphic rocks
formed from igneous rocks
77
New cards
Para-metamorphic rocks
formed from sedimentary rocks
78
New cards
1. Temperature 2. Pressure 3. Chemically active fluids
Metamorphic Agents
79
New cards
200° C
Minerals are normally stable at temperatures below {1}
80
New cards
1. The internal heat 2. The magmatic heat
Sources of heat for metamorphism
81
New cards
300°C - 850°C
Metamorphic changes take place between {1} - {2}
82
New cards
1. Uniform pressure 2. Direct pressure
Pressure causing metamorphism is of two types:
83
New cards
Directed pressure
can act in any direction
84
New cards
Uniform pressure
acts vertically downwards
85
New cards
1. These fluids act as carriers of chemical components that drive the chemical reactions with the minerals 2. The pore fluids undergo expansion, with rise in temperature 3. Fluids present around rocks may react with the minerals within them, at elevated temperatures