1. 3. ROCKS

2. Rocks are compact, semi-hard to hard mass composed of one or several minerals and/or mineraloids.
On the basis of their mode of origin, rocks can be divided into three basic types:
Igneous
Sedimentary
Metamorphic

3. ROCK CYCLE
The formation cycle of different types of rock and the processes associated with them. This is called the rock cycle.
Sedimentary
Rock
The rock cycle is important in any discussions of soil formation, especially if we know that soils are nothing but disintegrated rocks.
Metamorphic
Rock
Igneous
Rock

4. A. Igneous Rocks
They are those that have solidified from a molten or partially molten material called Magma or Melt.
Magma has originated well bellow the surface and ascended towards the surface, and has crystallized as solid rock either on the surface or deep within the earth's crust as temperature fell.
The types of igneous rock formed by the cooling of magma depends on the i) composition of the magma; ii) the rate of cooling associated with it.

5. Bowen’s Reaction Series
Bowen’s reaction principle—describes the sequence by which new minerals are formed as magma cools.
different chemical compositions with similar crystalline structures
different in their chemical composition and crystalline structure
Depending on the proportions of minerals available, different types of igneous rock are formed.

6. Bowen’s Reaction Series
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Two series of minerals formed during crystallization of magma
Temperature of
Crystallization
Low Silica Magma
Intrus. Extrus.
Gabbro Basalt
Diorite Andesite
Granite Rhyolite
1200oC
1000o
Frame Double Single Isolated
work Sheet Chain Chain
750o
High Silica Magma
CE 382 Geotechnical Engineering I st Semester 1436/1437 H

7. Mineralogy of Igneous Rocks
Many different types of minerals occur in igneous rocks, but only about eight are normally present as essential constituents of a rock. They are:
Quartz
Orthoclase
Plagioclase
Muscovite
Biotite
Hornblende
Augite
Olivine
Which of the eight are present is controlled primarily by the composition of the magma.

8. Classification of Igneous Rocks
I. Classification based on content of silica
The content of silica (Sio2) in igneous rocks varies from over 80% to about 40%. Rocks containing much silica were originally called ACID, and those with less silica were called BASIC.

9. Rock composition
Specific gravity
Amount of (SiO2)%
Typical Rocks
Color
Acidic
(Felsic)
>65
Granite
Rhyolite
light-colored
Intermediate
2.87
55-65
Andesite
Diorite
Light → dark-colored
Basic (Mafic)
45-55
Basalt
Gabbro
dark-colored
Ultrabasic
3-3.3
<45
Picrite
Peridotite

10. Igneous Rocks and Silicates
Frame Double Single Iso.
work Sheet Chain Chain
The
Igneous Rock Classification
parallels
the systematic
Silicate Mineral Classification
Mineral Percentage

11. II. Classification Based on Mode of Occurrence
A. Volcanic or Extrusive Rocks
They are formed when magma reaches the surface, along either wide vertical fissures or pipe-like openings in the earth crust.
B. Plutonic or Intrusive Rocks
Those rocks are formed when the magma rise through the earth’s crust but does not reach the surface.
Intrusions can be divided into two types:
1. Major Intrusions
2. Minor Intrusions
Stocks
Batholiths
Sheets
Dykes
Sills
Laccolith
phacolith

12. Extrusive/Volcanic: Igneous rocks that form due to the freezing of melts above the surface of the Earth.
Remark: In general Acidic lavas do not flow from their place of eruption in contrast to Basic lavas.

13. Intrusive/Plutonic:
Form by freezing of melts below the surface of the Earth.

14. Igneous Intrusions

15. Types of Igneous Intrusions
Discordant: cut across pre-existing fabric of rock layers
Dikes: are small igneous intrusions that cut across rocks into which the magma intrudes. They are commonly sheet-like, only a few meters wide, but possibly laterally extensive.
Stocks: are fairly large (10’s of miles) igneous intrusions that cut across pre-existing rock layers. In size, they are on the order of an individual mountain peak.
Batholiths: are huge igneous intrusions made of many stocks. Their size is on the scale of an entire mountain range (100’s of miles).

16. Laccoliths: are small intrusions having a flat floor and doomed roof.
Concordant: follow pre-existing fabric of rock layers without interruption of layering.
Sills: are also small igneous intrusions. They are sheets of rock that, unlike dikes, are parallel to pre-existing rocks. Think of magma invading sedimentary rocks by spreading out between rock layers. That magma would cool to form a sill.
Laccoliths: are small intrusions having a flat floor and doomed roof.
Phacoliths: are small intrusions having both a curved roof and floor.
Lopoliths: are also large, inverted mushroom-shaped (spoon-shaped) intrusions that “sag down” in the middle because of dense rocks.
Xenoliths are blocks of country rocks contained or enclosed into batholith rock.

17. Igneous Intrusions Remarks:
Dyke Swarm: is a group of parallel or radiating dykes.
One has to be careful when making site investigation not to confuse dykes or sills with major intrusions.

18. Tabular Intrusions: Plutons

19. Non-Tabular Intrusions: Plutons
Laccolith: a dome-like sill that bends the layers above it into a dome shape

20. Non-Tabular Intrusions: Plutons
Pluton: Irregular blob-shaped discordant intrusions that range in size from 10’s of m, to 100’s of km
Laccolith: a dome-like sill that bends the layers above it into a dome shape
Batholith: A pluton that is > 100 km2 in surface exposure
Stock: A pluton that is <100 km2 in surface exposure

21. Ultrabasic Basic Intermediate Acidic
III. Classification of igneous rocks based on composition and mode of occurrence
Ultrabasic
Basic
Intermediate
Acidic
ROCK COMPOSITION
MODE OF OCCURRENCE
Picrite
Basalt
Andesite
Rhyolite
EXTRUSIVE
Dolerite
Porphyrite
Felsite Quartz
MINOR INTRUSIVE
Peridotite
Gabbro
Diorite
Granite
MAJOR INTRUSIVE

22. Igneous Rock Classification (Summary)
Intrusive (Plutonic)
Extrusive (Volcanic)
Mineral Percentage

23. Classification of igneous rocks (Summary)

24. Igneous Rock Classification
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Igneous Rock Classification
Silicic Intermediate Mafic
Granite Diorite Gabbro
Rhyolite Andesite Basalt
(Porphyritic)
Intrusive
Extrusive
CE 382 Geotechnical Engineering I st Semester 1436/1437 H

25. B. Sedimentary Rocks Development
Sedimentary rocks are widely spread over the surface of earth. They constitute about 75% of the area of the continents.
Development
Weathering reduces the exposed rock mass to fragmented particles which can be more easily transported more easily by wind, water, and ice.
When dropped by the agents of transportation, they are called SEDEMENTS.
Sediments are typically deposited in layers or beds termed STRATA.
When compacted and cemented together (a process called LITHIFICATION), they formed sedimentary rocks.

26. The process through which sediments are converted into sedimentary rocks is called DIAGENSIS. It includes the following phases:
1. CEMENTATION
Water percolating through the voids (or pores) between the particles of sediment carries mineral matter which coats the grain and acts as cement that bind them together.
2. COMPACTION
The weight of top layers compacts sediments and expels water out.
3. CRYSTALLIZATION
Sometimes grains of sediments are joined together due to crystallization of some of their constituents due to pressure.

27. Mineralogy of Sedimentary Rocks
The composition of a given sedimentary rock will depend on:
The source of the waste material
The weathering process (Mechanical vs. Chemical)
The distance traveled
Minerals from pre-existing rock
Quartz
Feldspar
Mineral form in the area of deposition
Carbonates
Sulphates
Iron oxides
Silica

28. Classification of Sedimentary Rocks
Sedimentary rocks are classified into two major categories:
Detrital Sedimentary Rocks
They formed from minerals or rock fragments derived from the breakdown of pre-existing rock
Sedimentary Rock
Particle Term
Sediment
Conglomerate
Boulder
Cobble
Pebble
granule
Gravel
Sandstone
Very course sand
Coarse sand
Medium sand
Fine sand
Very fine sand
Sand
Shale
Mudstone
Silt
Clay
Mud

30. Conglomerate Sandstone Shale
This is a rock consists of cemented boulder, cobbles, pebbles and granules.
Sandstone
This rock is composed essentially of pressure- cemented grains of sand. The cement agent determines the degree of indurations, or hardness, of sandstone.
Shale
It is formed from silts and clays which have hardened into rock, with the principal indurations agent being pressure.

31. REMARKS
1. Breccia is a variety of conglomerate, which has angular rather than rounded fragments.
2. When the grains in sandstone are practically all quartz, the rock is referred to as orthoquartzite.
3. For Sandstone, the three chief kinds of cement, in the order of their importance are:
Silica
Iron oxides
Carbonates
4. Mudstone has a blocky aspect; whereas, in the case of shale, the rock is split into platy slabs.

32. 5. In mudstone and shale, size of the particles are generally less than 1/16 mm.
6. Shale is the most abundant of the sedimentary rocks. Nearly half of all the sedimentary rocks are shale.
7. Marl is a calcareous mudstone (expansive).
8. From engineering point of view, sedimentary rocks are the most important and relevant because:
They are the most abundant, and hence encountered.
They are the most problematic.

33. II. Chemical Sedimentary rocks
Sedimentary rock also can be formed by chemical processes. Rocks of this type are classified as chemical sedimentary rock.
Examples of Chemical Sedimentary Rocks:

34. Remarks
If a carbonate rock contains more than 50% of sand –sized quartz grains, the rock is termed a CALCAREOUS SANDSTONE.
If it contains more than 50% clay, the rock is termed a CALCAREOUS SHALE.
If It contains more than 50% calcite, the rock is called LIMESTONE.
If It contains more than 50% dolomite, the rock is called DOLOMITE.
The name dolomite is used to designate both a mineral and a rock. In order to avoid the confusion, some label the rock DOLOSTONE.

35. Textures of Sedimentary Rocks
There are two main types of textures of Sedimentary Rocks:
1. Clastic Texture
Rocks formed by mechanical weathering have clastic texture
2. Non-Clastic Texture
Most chemical sedimentary rocks have a non clastic texture. These rocks have somewhat the same appearance as igneous rocks with crystalline texture.

36. Summary of Sedimentary Rocks
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Summary of Sedimentary Rocks
CE 382 Geotechnical Engineering I st Semester 1436/1437 H

37. Features of Sedimentary Rocks
Sedimentary rocks have several key features.
1. Sorting
Well-sorted versus poorly sorted.
Common examples: Graded Bedding, Cross Bedding

38. Features of Sedimentary Rocks (cont.)
2. Stratification
Most sedimentary rocks are layered and the layers range in thickness from mm to meters.
Such depositional layers are called STRATA, an individual layer is a STRATUM.
In everyday language, the layers are called BEDS, if the layer thickness is > 1 cm. if < 1cm they are called LAMINE.

39. 3. Roundness of grains

40. 4. Ripple Marks

41. C. Metamorphic Rocks
Metamorphic rocks are formed if a rock is subjected to increase in temperature, pressure, or both, to such degree that a new TEXTURE or possibly a new MINERAL composition is produced.
The process of change is referred to as METAMORPHISM. It is derived from the Greek META which means change and MORPH, shape or form.
The original rock may be igneous, sedimentary or metamorphic.

42. The origin of metamorphic rocks is the least clear among the three classes of rocks. Because no one has ever seen a metamorphic rock been formed, and for that reason many of our ideas about them are pure conjecture.
During metamorphism the minerals do not melt, but remain largely in the solid state.
The metamorphism process is isothermal process, i.e. the overall chemical composition of the rock is nearly the same before and after recrystallization.

43. Classes of Metamorphism
There are three broad classes of metamorphism depending on the control exercised by temperature and pressure.
1. Thermal or Contact Metamorphism
Increased temperature is the dominant agent producing change. (Caused by igneous activity)
2. Dynamic or Dislocation Metamorphism
The dominant control is stress, extra heat is relatively unimportant. (Associated with faults & earthquake zones)
3. Regional Metamorphism
Both temperature and pressure have operated over a large (regional) area. (Associated with tectonic plate activity).

44. The degree of metamorphism is related to the conditions of temperature and pressure under which the new metamorphic rock has formed, and may be assessed by the appearance of certain minerals.
The index minerals each of which indicates a particular temperature and pressure at the time it formed are used to define the metamorphic GRADE of the rock in which they occur.
One important characteristic related to the metamorphic grade is that grain size gets coarser with higher grade, i.e. rocks formed at higher temperature have coarse grained particle like GNEISS, and vise versa.

45. Some metamorphic rocks and their original rocks
Slate
Mudstone, Shale
Sedimentary rocks
Quartzite
Sandstone
Marble
Limestone
Hornblende
Dolerite
Igneous Rocks
Biotite
Diabase
Plagioclase
Augite&Chlorite
Granulites
Gabbro

46. Non-Foliated Moderately Foliated Well-Foliated
CLASSIFICATION OF METAMORPHIC ROCKS
I. Classification Based on Type of Metamorphism
Contact Metamorphic Rocks
Dynamic Metamorphic Rocks
Regional Metamorphic Rocks
II. Classification According to Degree of Foliation (Textures)
Non-Foliated
Moderately Foliated
Well-Foliated
Quartzite
Gneiss
Slate
Marble
Migmatite
Phyllite
Hornfels
Granulite
Schist
Serpentine
Mylonite
Amphiblite

47. Foliated Non-Foliated Rock has distinct banding or layering
Formed under direct pressure
Non-Foliated
No distinct layering character
Formed under uniform pressure

48. Foliated Metamorphic Rocks
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Foliated Metamorphic Rocks
slate
phyllite
schist
gneiss
CE 382 Geotechnical Engineering I st Semester 1436/1437 H

49. iii. Classification of metamorphic rocks according to metamorphic grade

50. iv. Classification of Metamorphic Rocks based on their Composition
1. Monomineralic
Metamorphic rock composed predominantly of single mineral
For example, Marble: calcite and Quartzite: quartz
2. Multimineralic
Metamorphic rock composed predominantly of two or more minerals
For example, Gneisses: felsic and darker mineral layers

51. Classifications of Rock Masses for Engineering Purposes
1. We can say in summary that classification in general provides:
A language of communication between engineers
A basis for understanding the characteristics of each rock mass class
Quantitative data and guidelines for engineering design
Relate the experience of rock conditions at one site to the conditions and experience at other.

52. 2. Rock Mass Property and Classification
Rock mass is a matrix consisting of rock material and rock discontinuities. Properties of rock mass therefore are governed by the parameters of i) rock joints and ii) rock material, as well as iii) boundary conditions.
Prime parameters governing rock mass property
3. Rock Mass Classification Systems (See Distributed Table).