NOTS ON LAMPROPHYRES

INTRODUCTION

The term lamprophyre was introduced by Gumbel (1874), to describe a group of dark colored dyke rocks from West Germany. In Greek the word “lampros” means bright or glistering. The rock collected from West Germany was bright due to biotitic flakes.

According to IUGS Sub-Commission lamprophyres are defined as follows. “They are distinct group of rocks, which are strongly prophyritic with mafic minerals, typically made up of biotite, amphiboles, pyroxene, feldspars and foids. They commonly occur as dyke or small intrusions showing hydrothermal alteration”.

CLASSIFICATION

Lamprophyres are classified into three groups. 1. Calc- Alkaline lamprophyres. 2. Alkaline lamprophyres, 3 Melilitic lamprophyres. The Calc Alkaline lamprophyres are called ordinary lamprophyres. The common members are Minette, Vogasite, Kersantite and Spessartite. In the alkaline lamprophyres, Sannaite, Camptonite and Monchiquite are grouped. Alnonite, Polzenite are called Melitite group.

MINERALOGY

Mica, amphibole, clinopyroxene, melilite are commonly occurring dark colored mineral. Usually they occur as phenocrysts. In the groundmass alkaline feldspar, plagioclase feldspar, foids, carbonates and mica are found. Petrographically, lamprophyres are showing porphyritic texture, but pan idiomorphic is common. Geochemically, they are enriched in K₂O and Na₂O. But generally they are ultra-potasic. High magnesium and iron are characteristic. Invariably lamprophyres are concentrated with H₂O, CO₂, S, P₂O₅ and Ba. They also have higher LREE. In the field lamprophyres occur as minor hypabyssal intrusions. They also found as sill, dyke, stocks, pipes and volcanic necks. Generally calc alkaline lamprophyres are found as multiple plutonic bodies.

ORIGIN OF LAMPROPHYRES

Lamprophyres are produced from alkaline magmas. These alkaline magmas are derived from lower crystal or upper mantle melting processes. When these alkaline magmas or lavas are contaminated, the lamprophyres are produced. Addition of volatile contents such as H₂O and CO₂, assimilation of alkaline materials may be the main cause for generation of lamprophyric liquids.

Lamporites are a group of alkaline rocks similar to lamprophyres they are mostly sub volcanic and extrusive. They differ from lamprophyres in mineralogy and higher SiO₂ content. They are having low foid content than lamprophyres. Lamporites are having diamonds and are close in association with Kimberlites.

INDIAN OCCURRENCES

In India lamprophyres are associated in coal fields of Raniganj and Bokkaro in the form of dykes. Minette is found Kurnool District of Andhra Pradesh. Comptonite is found in Kishangarh in Rajasthan.   Monchiquite is found in Mt.Girnar where as olivine Vogasite is found in Salem districts.

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Solar System

The Solar System

The Solar System is the name given to the Sun and its family of planets. This family of planet consists of eight planets and a belt of minor planets or asteroids. They all move in elliptical orbits around the sun due to its force of gravitational attraction.

The eight major planets in the Solar System are:

1. Mercury
2. Venus
3. Earth
4. Mars
5. Jupiter
6. Saturn
7. Neptune
8. Uranus

Pluto was considered to be the ninth planet until 2006 when it was reclassified as a dwarf planet. It has an orbit more common with asteroids rather than the other planets and astronomers suspect that it might once have been a moon of Neptune.

Astronomers have divided the eight major planets into two groups: terrestrial and Jovian.

Terrestrial Planets

The terrestrial planets are Mercury, Venus, Earth and Mars and are made up mostly of Iron and silicate rocks and lie closer to the Sun.

Jovian Planets

The Jovian planets are Jupiter, Saturn, Uranus and Neptune and are made up mostly of Hydrogen and Helium. Because of their gaseous composition they are also referred to as the Gas Giants. The Jovian planets are the larger more massive planets with strong magnetic fields and they rotate more rapidly about their axes. Unmanned space probes have shown the Jovian planets have ring systems with moons orbiting them.

The Sun

The sun lies in the centre of the Solar System. It is a yellow dwarf star. It has a surface temperature of approximately 6000°C. Its diameter is about 865,000 miles approximately 109 times the diameter of the Earth. By mass the sun is made up of 71% Hydrogen, 28% Helium and the remaining 1% mass comprising heavier atoms such as Carbon, Nitrogen, Oxygen, Silicon and Iron. The sun contains 99% of the Solar Systems mass. It has no fixed surface and the temperature is too high for the matter to exist as a solid or a liquid. Due to this different parts of the sun rotate at different rates. The parts of the surface near the equator complete a rotation in 25 Earth days, whereas the parts near the pole take 36 days.

Mercury

Mercury is the smallest of the eight planets in the solar system. It is the planet with the closet orbit to the sun. Its orbit lies between the sun and the orbit of Venus and it has no known moons. Mercury has a diameter of approximately 3000 miles. It is made up of a high percentage of metal making it the densest planet in the solar system. It takes Mercury 88 Earth days to orbit the sun. The fast orbit is offset by the planets slow spin. It takes Mercury 59 Earth days to complete one rotation about its axis.

Venus

Venus is the second planet from the sun. Its orbit lies between the orbits of Mercury and Earth and has no known moons. It is the closest planet to the Earth and after the moon is the most brilliant natural object in the night sky. Venus has a diameter of approximately 12,100 km making it slightly smaller than Earth (Earth’s diameter is approximately 12,750 km). Although further away from the sun than Mercury, Venus is the hottest planet in the solar system. This is because it has a very large atmosphere made up mostly of Carbon Dioxide. This thick, dense atmosphere traps the heat radiated from the planet’s surface and the sun (greenhouse effect) making the average temperature on Venus about 460°Celsius. Venus spins about its axis very slowly taking 243 Earth days to complete one rotation, which is the length of a day on Venus. It completes one orbital revolution of the sun in 225 Earth days making Venus the only planet where a day is longer than a year. Venus rotates about its axis in a retrograde motion i.e. in a direction opposite to the other planets. Venus and Neptune are the only planets which rotate counter clockwise while the other 6 planets rotate clockwise.

Earth

Earth is the third planet from the sun. It is the only planet that hosts all known life. Its orbit lies between Venus and Mars and has one moon. The Earth has a diameter at the equator of 12,756km. It spins about its axis once every 24 hours (1 Earth day) and takes 365.256 days to orbit the sun. The Earth’s atmosphere is made up of 78% Nitrogen, 21% Oxygen and the remaining 1% consists of other gases such as Argon, Carbon Dioxide, Methane and Hydrogen.

Mars

Mars is the fourth planet from the sun. The orbit of Mars lies between Earth’s orbit and Jupiter’s orbit. Between Mars and Jupiter lies the main asteroid belt. Mars has two small moons called Phobos and Deimos. Mars is the second smallest planet in the solar system. Its diameter at the equator is approximately 6,800km. It takes Mars 687 days to complete one revolution of the sun. Thus, one year on Mars is equivalent to almost 2 Earth years. Mars is called the red planet due to the reddish brown Iron Oxide on its surface. Its atmosphere is made up mostly of Carbon Dioxide, however the atmosphere is very thin making the average temperature on the surface average about -70°Celsius.

Asteroid Belt

Asteroids are chunks of metal and rock much smaller than the planets that orbit the sun. Most of the asteroids in the solar system are found in the asteroid belt a region between the orbits of Mars and Jupiter. It is considered by astronomers that during the formation of the solar system the immense gravitational pull from Jupiter prevented the asteroids from joining together to form a planet.

Jupiter

Jupiter is the fifth planet from the sun. It is the largest planet in the solar system with a diameter at the equator of approximately 143000km. More than 1300 Earths can fit inside Jupiter. Jupiter holds more matter than all the other planets in the solar system. Its strong gravitational pull is accountable for the many moons that orbit the planet. To date more than 60 known moons orbit Jupiter. It completes one rotation in 9hours 55 minutes, which is the length of a day on Jupiter. It takes about 11.9 earth years to orbit the sun. Jupiter has no solid surface. It is composed mainly of Hydrogen and Helium. The large pressures in the planets interior account for Hydrogen and Helium in the liquid form surrounded by a gaseous atmosphere. The Great Red Spot is a huge oval shape storm system in the planets southern hemisphere.

Saturn

Saturn is the sixth planet from the sun. After Jupiter it is the second largest planet in the solar system. Its diameter at the equator is approximately 75000 miles (120,500 km). Saturn’s orbit lies between Jupiter and Uranus and it takes about 30 Earth years to complete one revolution around the sun. It rotates about its axis in 10.8 hours, which is the length of a day on Saturn. Saturn like Jupiter is one of the gas giants and is composed mostly of Hydrogen and some Helium. Saturn’s most famous feature is its ring system. This is made up of hundreds of thousands of individual rings held in orbit by the pull of Saturn’s gravity. The rings are made up of countless ice chunks and dust particles. In addition to the ring system there are more than 50 known moons that orbit Saturn.

Uranus

Uranus is the seventh planet from the sun. Its diameter at the equator is about 32000 miles (51500 km) making it the third largest planet in the solar system. It takes Uranus 84 Earth days to complete one trip around the sun. Uranus completes one rotation on its axis in approximately 17 Earth hours, which is a length of a day on Uranus. Uranus is different to the other planets in that its rotation axis lies nearly to its side as it goes around the sun. Like Venus it rotates about its axis in a retrograde motion. Scientists think that this alignment may have been caused by violent collisions with other bodies early in its history. Uranus has a liquid interior due to very high temperatures and pressures inside the planet. It is made up of the melted ices of water, methane and ammonia, along with molten rock and metals and small amounts of Hydrogen and Helium. Uranus has a massive atmosphere made up of approximately 75% Hydrogen and 25% Helium with small amounts of methane, water and ammonia. Uranus has a system of about 12 narrow rings; the rings are made up of countless particles orbiting the planet. Uranus has 5 major moons and more than 20 smaller ones.

Neptune

Neptune is the eight and farthest most planet from the sun and cannot been seen by the unaided eye. It has a diameter of approximately 31000 miles (50000 km). It takes Neptune 146 Earth years to orbit the sun. Neptune takes 16 hours to complete one rotation about its axis, which is a length of a day on Neptune. Like the other gas giants Neptune has a massive atmosphere made mostly of Hydrogen with some Helium and about 2% of Methane. It is the Methane in Neptune’s atmosphere that makes it appear bluish in colour. The interior is similar to Uranus being made up of melted ices of water, Methane and Ammonia, along with molten rocks and metals. Neptune has 6 narrow rings composed of dust size particles orbiting the planet. Neptune has 13 known moons.

Pluto

Pluto was discovered in 1930 and was considered the ninth planet of the solar system up until 2006 when it was classified as a dwarf planet. This was due to many other objects of a similar size to Pluto being discovered in a region where it lies called the Kuiper belt. So, rather increase the number of planets each time a new object was discovered the definition of planets was redefined to exclude objects such as Pluto and a new category called dwarf planets was designated for Pluto. Pluto has a diameter of about 1500 miles (2400 km). It takes Pluto 248 years to complete a trip around the sun, which is the length of a year on Pluto. It completes one rotation about its axis in 6.4 Earth days. Its atmosphere is composed of Nitrogen with small amounts of Methane and Carbon Monoxide. Its ineterior is thought to be made of rock and ice. Because of its great distance from the sun the surface temperature on Pluto is extremely cold. Pluto has one known moon.

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Center of the earth

Center of the earth:

The first thing to remember is that NOBODY has ever been there, so what you are about to hear is barely past the Wild and Crazy Idea stage. What we think we know comes from a study of how earthquake (seismic) waves travel through the earth, and how long it takes for them to get from where the earthquake happens to a recording station. The basic idea is that different materials transmit seismic waves at different speeds. With a lot of earthquakes and a lot of recording stations, geophysicists are beginning to get a pretty detailed picture of what is probably down there.

One of the most distinctive features of the earth's interior is how it seems to be layered by density, with the heaviest stuff in the center, and the lightest material at the surface. In fact, the earth probably looks a lot like a hard boiled egg if you could cut it open. The yellow stuff in the center (the yolk) relates to what we call the core. Most geophysicists think that the core is composed of high density materials like iron and nickel. The egg's shell is like the earth's crust - a thin veneer of rigid, low density material at the surface. And all the white stuff in between is like the earth's mantle - the largest layer which, in the case of the earth, is of medium density, and, in the case of an egg, tastes best with a bit of salt and pepper.

The core seems to be in two parts - a "solid" inner core with a "liquid" outer layer - and is the final resting place for as much of the high density material as can get there. The crust is REAL thin relative to the size of the earth - much, much thinner than an eggshell, and is of much lower density than the core. It is probable that the mantle represents the vast majority of the earth's mass which is still trying to figure out if it is heavy enough to be accepted at the core, or is lower in density and therefore has to float about on the surface with the rest of the scum.

There is another way to describe the regions of the Earth, especially those near the surface of the Earth. This description is nicely shown below.

This diagram introduces us to a few new terms that we need to know in order to understand how the structure of the Earth allows for plate tectonic activity. When we familiar with the crust of the Earth shown in the first diagram. The distinction between the crust and mantle is based on chemical differences between the two regions. The transition between the crust and mantle is sharp (discontinuous is the word often used in science to describe sharp, non-gradual transitions), with the rocks of the mantle being noticeably denser (and darker in color) than the rocks of the crust. However, the crust and upper portion of the mantle are fused together to create a rigid, rocky layer called the lithosphere. The lithosphere floats on a partially fluid, "slushy" region called the
asthenosphere (asthenosphere mean "weak layer" in Greek; this region is also referred to as the "Low Velocity Layer" because seismic (earthquake) waves travel slowly through this region of the Earth.)

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GIS in ENGINEERING GEOLOGY

INTRODUCTION: 
A full three-dimensional GIS system is obviously the best system to handle engineering geological data and analyses. For regional studies, this may lead to very extensive databases and consequently long calculation times, although this may become unimportant with further development of computer power. In regional studies, if property distributions are not important and the geology is relatively simple, a 2.5D system may be sufficient.

A full 3D-GIS system is necessary for site-specific analysis in which either an accurate representation of the sub-surface is required and/or property distributions are required, or where the geology is more complicated. Figure shows an example of a sub-surface property model for a tunnel project and Fig. shows the application for a dam project. Geographical Information Systems, and in particular 3D-GIS, are able to offer considerable help to the engineering geologist however, it does not add these qualities in itself. The quality of the output is directly related to the quality of the input and the quality of the manipulation that is done with the data, e.g. “rubbish in” is still “rubbish out”. Another point that should be considered is that GIS software is complex and not always user friendly. Hence, it is often time consuming to use the programs and this extra time is certainly not always justified for all type of projects. Some professionals, probably it should be questioned whether these are professionals, cut down on time consuming operations by using simple programs, for example, 2.5D instead of the more complicated 3D programs, and by using simple calculation routines when more complicated but better relations are known. Obviously, GIS used in this way can result in lower quality results than traditional methods.

Quality of Published Information and Limitation of Liability: Maps, whatever their character, contain such information as was available at the time of their compilation, which is often out of date at the time of publication and later use. Information that contains an interpretation of available data, give those opinions based on the understanding of the engineering behavior of the ground of that time, which is not necessarily that of the time of later use. If information expresses opinion, which is virtually always the case with geology interpretations, the question arises as to who is responsible for the quality and accuracy of that opinion. The types of maps which are published by government agencies in any one country depend, therefore, upon the social, political and legal systems in that country because if engineering works are planned on the basis of the information provided by these maps, there must be some understanding as to who is responsible for the validity of the data they present.

An Aid to Engineering Geological Mapping: As an aid to engineering geological mapping the author developed the system discussedbelow. Regional scale engineering geological mapping must have purpose. The rockmass classification described below is aimed at distinguishing between those rockmasses which pose no particular problems for general civil engineering to be conductedon or in them from those which will give problems.

Factors in the PRI:

The factors considered in the Problem Recognition Index are:

1.       Layer strength

2.       Layer uniformity

3.       Discontinuity spacing

4.       Uniformity of surface weathering profile

5.       Material sensitivity to weathering or alteration

Layer Strength Rating (LS): Rock strength is an obvious parameter of considerable significance in most forms ofengineering in rock. Ratings assigned vary from 10 for strengths less than 1.25 MPa to 100 for strengths greater than 200 MPa. However, some allowance must be given for anisotropy. In the field, layer strengths are measured in two orthogonal directions, which, in bedded rocks, would be normal and parallel to the bedding, using a Schmidt hammer or by geological hammer blows.

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Branches of GEOLOGY

INTRODUCTION:

Broadly stratigraphy deals with the succession of geologic events and / or rock layers from the beginning of the crustal formation up to the present time. It aims at establishing and describing the correct order of superposition of rock-units on the earth's surface. Thus, it actually establishes the correct succession of rock formations / layers. It thereby unfolds the history of geological events on the earth from the geologic past to the present time and hence it is also referred to as historical geology as a synonym.

Geology is divided into several fields, which can be grouped under the major headings of physical and historical geology.

Physical Geology: Physical geology includes mineralogy, the study of the chemical composition and structure of minerals; petrology, the study of the composition and origin of rocks; geomorphology, the study of the origin of landforms and their modification by dynamic processes; geochemistry, the study of the chemical composition of earth materials and the chemical changes that occur within the earth and on its surface; geophysics, the study of the behavior of rock materials in response to stresses and according to the principles of physics; sedimentology, the science of the erosion and deposition of rock particles by wind, water, or ice; structural geology, the study of the forces that deform the earth's rocks and the description and mapping of deformed rock bodies; economic geology, the study of the exploration and recovery of natural resources, such as ores and petroleum; and engineering geology, the study of the interactions of the earth's crust with human-made structures such as tunnels, mines, dams, bridges, and building foundations

Historical Geology: Historical geology deals with the historical development of the earth from the study of its rocks. They are analyzed to determine their structure, composition, and interrelationships and are examined for remains of past life. Historical geology includes paleontology, the systematic study of past life forms; stratigraphy, of layered rocks and their interrelationships; paleogeography, of the locations of ancient land masses and their boundaries; and geologic mapping, the superimposing of geologic information upon existing topographic maps.

Paleontology: It deals with the morphologic characteristics, modes of preservation, taxonomic classification, and geological history of the ancient lives - both invertebrates, vertebrates and of plants. Fossils are remains of geologically very old and ancient lives in form of entire body or hard parts, which are calcified, and / or silicified (petrified) in form of molds and casts or as traces of remains / relics which are preserved in various modes within sedimentary strata.Fossilization is a natural process. Fossils have important uses in the fields of bio-stratigraphic correlation, palaeo- climatic interpretation, top and bottom criteria for correct stratigraphic interpretation, polaeogeographic reconstruction and economic geology field for their different utilitarian aspects.

Economic Geology: It is the branch that deals with various geologic and geo-economic aspects of the vast array of metallic, non-metallic, industrial minerals and some specific rocks and the fuel minerals such as petroleum, natural gas, coal, radioactive minerals and geothermal sources. This branch describes the useful minerals (ore and nonmetallic minerals) in respect of their commercial value (metal contents) mode of occurrence, classification, grades, uses and origin.

An applied aspect of this important branch includes geological exploration, value assessment of economic deposits, mining, beneficiation, reserve estimation and different aspects of mineral economics. The applied aspects of this branch have great bearing on the formulation of conservation measures that leads to a National Mineral Policy for the country.

Engineering Geology:  This applies the geologic basics to the field of engineering structures such as dams, reservoirs, tunnels, bridges and embankments, in which concepts of geology and civil engineering are given nearly equal weightage to construct engineering structures in the most suitable and safe geologic sites recommended by geological studies. Geologist recommends a few favorable site choices and one of them is finally selected paying equal weightage to geo-safety and engineering feasibility of total cost factors.

Marine Geology: This allied branch deals with the application of geological knowledge in evaluating the favorable locales in the littoral, offshore and shelf regions to explore into the realm of marine sedimentary sites to describe the coastal geomorphologic characteristics, the presence of offshore oil and gas reservoirs and vast mineral wealth of black sand beach placers.

Hydro-geology: Also termed as geohydrology, it deals with mode of occurrence, movements, qualitative and quantitative nature of ground water present in the zone of saturation below the surface. The characteristics of water-bearing and conducting strata (the aquifers) are studied to assess the ground water potential in terms of quantity and quality.

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Role of engineering geology in engineering

INTRODUCTION: 
The overall success of the river linking is based on the engineering safety of the dams. Channels and structures in the link. As geological conditions that would lead to failure of tunnels, dams. Aqueducts and erosion of channels are of common occurrence a geological study of the linking channels is essential. While comparing the cost of a tunnel with that of an open channel, the cost of protection works required for the tunnels and channels must also be taken into account. Dams required to divert the channels as well as the foundations of the aqueducts will also have to be properly investigated in engineering geological perspective. Sufficient time will usually be available to carry out the necessary geological investigations

And to design and to execute appropriate protective works. But it is important to take cognizance of the problem immediately as it manifests itself and to proceed scientifically to tackle it.

Aqueducts in River Linking Project: While carrying water through different regions,thousands of cross drainage works will have to be 'constructed. Very high and long aqueducts will haveto be designed before construction. Propergeological investigation of the foundations of allsuch structures is very important. The success of thewhole: project is depending on the engineeringsafety of channels, structures and dams in the link.

DAMS IN THE RIVER LINKING PROJECT:Dams are key structures in river linking schemes. In such projects besides the existing old dams, new darns or di version barrages will have to be planned. Besides being a source of wealth, darns can also be a source of accidents, albeit it few in number: an average of less than 1% of dams has suffered accidents over a long period of time. Yet the resulting damage and loss of life mean that all such accidents are unacceptable. A dam prevents the flow of water on surface, but if water is to be stored, it has also to be seen that there is not a flow below the surface either. This means that the foundation rocks must be watertight, and if they are not naturally so, suitable steps have to be taken to prevent loss of water through them. Also, to avoid the disastrous effects of dam failure safety and stability of a dam have to be assured. These will depend among other things on the strength and soundness of foundation rocks, which in turn will depend on the nature and structure of these rocks. An analysis of dam failures of the past has shown that failure to recognize or to treat properly defects in foundation rocks was responsible for a substantial number of them. The safety, stability and effectiveness of a dam therefore will depend largely on the geological conditions at the foundation and these must be known with accuracy and in sufficient detail before the work on a dam is undertaken. Detailed geological investigations have therefore to be carried out for obtaining the necessary information about rocks at the dam site and over the reservoir area

TUNNELS IN RIVER LINKING PROJECT: Tunnel is a very essential component now-a-days in a dam project. The modernized methods andexperience in tunneling techniques-enables an engineer to opt 'for the tunnels. However engineering geology plays very important role for a successful tunnel. Proper knowledge of thestrata and investigation by proper geologist is therefore very important. Collapse of a bottlenecktunnel may prove a total project economically unsafe.

GEOLOGY OF MAHARASHTRA: About 85% of Maharashtra is covered by igneous volcanic rocks- Deccan trap basalts. In rest of

The portions older rocks belonging to Archaen, Dharwar, Cuddapah, Vindhyan and Gondwana series of Indian Geology occur. The Deccan Traps mainly consist of basalts, but as there is considerable variation in the characteristics of basalts, and as rocks. Derived from them by modifications taking place in the volcanic process also occur. It is proposed to describe here some case histories of dams, at which we have carried out geological work, in an attempt depict the varying geological conditions in the Deccan Trap rocks that effect tunneling operations.

THE DECCAN TRAP ROCKS: As the suitability or otherwise of geological conditions for tunneling will depend on thecharacteristic of rocks met with along the alignment, an acquaintance with the various rock typesoccurring commonly in the Deccan Traps and their engineering behaviors is necessary.

Compact and Amygdaloidal Basalts: In the Deccan Trap basalts two main types occur: The compact nonvascular basalts without gascavities filled with secondary minerals such as zeolites. And chlorophaeite which give themspotted appearance. Both compact and amygdaloidal basalts often contain small slender laths asphenocrysts giving polyphyritic varieties.

Chlorophaeitic Basalts: Chlorophaeitic basalts in which a major portion of groundmass glass has been converted intochlorophaeite are common. When large amounts of chlorophaeite are present the rocks becomedark black.

Hydrothermal Alteration: Magmatic gases that produce cavities sometimes chemically alter the basalts, and this action iscalled hydrothermal alteration. The normal grey or bluish color of basalts is turned into shadesof green. Pink. Red. Purple or brown by hydrothermal alteration. Most commonly hydrothermalalteration brings about only such color changes in basalts without affecting their physicalproperties but more intense hydrothermal alteration at times weakens rocks.

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Geological materiyal

INTRODUCTION:
Engineers work with large volumes of soil and rock which will contain variable amounts of fluid in their pores and fractures. It is helpful to distinguish the material from which these volumes are made from the mass which they form. Sediments are made from particles, big and small, and “rocks” are made from rock!

Sediments: The coarsest sediments are those produced by land sliding and glaciation which maytransport fragments of rock so large that an examination at close range may fail torecognize that they have been displaced. More commonly, rock fragments found beloweroding cliffs may be many tones in weight. Such very large fragments may befurther eroded during river transportation to gravel and boulder size. These fragmentsare recognizably rock but, as they disintegrate to yet smaller and sand-size grains, thegrains tend to be largely of single minerals. The type of mineral of which they are composed will depend upon the source rock and the degree of abrasion suffered during transportation.

Thus the most common sand-forming mineral is quartz, but in limestone areas the grains may be predominantly calcareous. If there are local sources of less erosion-resistant minerals, such as mica, these may be found mixed with more resistant minerals transported from distant sources. Grains of all sizes will be, to some degree, rounded by abrasion during transportation and the degree of roundness achieved is of geotechnical significance, for angular grains tend to interlock and give greater shear strength than more rounded grains. Uniformly graded sediments comprise more or less equally distributed representatives of many grain sizes. Well graded sediments are mostly of one grain size while gap graded sediments lack a range of grain sizes. Well graded sediments tend to have greater porosity and thus greater permeability than uniformly graded sediments because there are fewer finer particles to fill pore spaces between larger particles. At silt size, the particles and the pore spaces between them are very small so that permeability is very low and movement of water slows. For this reason, attempts to compact water saturated silt may result in raised pore water pressures and the subsequent liquefaction of the deposit.All of the sediments so far described are granular and the grains do not adhere to each other. The yet finer grained sediments, clays, are formed of particles less than 0.002 mm in diameter and often much smaller, and are commonly very small plates of clay minerals bonded together by electro-chemical forces. This bonding gives the clay cohesion allowing the material to be moulded. Clay minerals result mainly from the weathering of other rock forming minerals. Thus kaolinite results from the weathering of feldspars in granitic rocks.

Intact Rock Materials: ‘Intact’ rock is commonly taken to mean a piece of rock about the size of a laboratorytest specimen (usually a cylinder of core no larger than about 100 mm long and 50 mmdiameter) without obvious cracks or breaks. Most rocks are formed of mineral grainsor other rock fragments bonded together in some way. The amount of pore spacepresent, the size of the pores and the nature and quantity of the cement has a majoreffect on the mechanical properties of the intact rock material. In general terms, thegreater the porosity, the weaker the rock and, of course, the weaker and less abundantthe cementing mineral, the weaker the rock also.No rock can be stronger than the minerals of which it is composed and the natureof the rock forming minerals has a dominating influence on the behaviour of some rocks. Thus rocks formed from soluble minerals such as calcite and gypsum, pose problems from past solution and future solubility. Evaporites are effectively monomineralic rocks whose formation is associated with the evaporation of mineral charged water. They include such minerals as halite (rock salt), gypsum and anhydrite and potash salts (such as a carnallite and polyhalite). Evaporites, particularly rock salt, will flow under pressure and may be found in salt domes pushed, and still moving from their original position, upward into overlying strata. The susceptibility of these rocks to creep gives problems in mines and tunnels.

Fluids and Gasses: The main fluids of importance in engineering geology are water and oil. It is almostimpossible to over-emphasize the importance of water in determining the engineeringbehavior of geological materials and masses. Water is almost incompressible andwhen present in the pore spaces of a material, if only in small amounts, will modifythe behavior of that material under stress. The behavior of clays, in particular, isvery much dependent on moisture content. Water is seldom pure and contains dissolvedminerals, such as sulphates, which may react with engineering materials. Salinityand acidity limits its use in such processes as the manufacture of concrete. Onfreezing, water expands and ground heave and ice wedging are important mechanismscausing ground disruption and slope instability.

Oil as a fluid in the ground is not often of direct importance in civil engineering unless there are projects proposed at great depth in which oil may be inadvertently encountered. However, it is a common cause of contamination in industrial sites and becomes a component of sediments that has to be considered when such sites are redeveloped.

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