Diamond

They are mined from kimberlite and lamproite volcanic pipes, which can bring diamond crystals, originating from deep within the Earth where high pressures and temperatures enable them to form, to the surface. A diamond is a transparent crystal of tetrahedrally bonded carbon atoms and crystallizes into the face centered cubic diamond lattice structure. 

Diamonds have been adapted for many uses because of the material's exceptional physical characteristics. Most notable are its extreme hardness, its high dispersion index, and extremely high thermal conductivity (900 – 2320 W/m K), with a melting point of 3820 K (3547 °C / 6420 °F) and a boiling point of 5100 K (4827 °C / 8720 °F). Naturally occurring diamonds have a density ranging from 3.15 to 3.53 g/cm³, with very pure diamond typically extremely close to 3.52 g/cm³.

The conditions for diamond formation to happen in the lithospheric mantle occur at considerable depth corresponding to the aforementioned requirements of temperature and pressure. These depths are estimated to be in between 140–190 kilometers (90–120 miles) though occasionally diamonds have crystallized at depths of 300-400 km (180-250 miles)

Minerals and Rocks

Minerals are natural chemical substances of inorganic origin. Most rocks are composed of minerals, but some are of organic origin, and others consist of natural glass.

A mineral is typically a crystalline substance, having regular atomic pattern. When conditions are favorable, minerals develop definite geometric forms called crystals. These are classified in six crystal systems according to the number, relative lengths, and regular relationships of imaginary lines called axes.

Most rocks are composed of silicate minerals, consisting of a silicon atom surrounded by four oxygen atoms in a tetrahedral pattern. Attached to the oxygen atoms are atoms of other elements, of which six—aluminum, iron, magnesium, calcium, sodium, potassium – are the most common; oxygen, silicon, and these six other elements make up most of the crust of the earth.

Many minerals are commercially or scientifically important even though not essential to the forming of the common rocks. Some are ores, others are so-called industrial (nonmetallic) minerals, and some  have considerable scientific interest.

Rocks formed by the solidification of molten matter  are termed igneous. These are regarded as the primary rocks –not being derived from still older rock—although none of the original crust of the earth is believed to exist, for it has presumably been reworked more than once.

Rocks formed by the breakdown of other rock are called sedimentary. They may accumulate as fragments, or they may deposit from chemical solutions.

Either igneous or sedimentary rock may be slowly changed into metamorphic rock by heat, pressure, and solutions. Most metamorphism occurs as a result of mountain building, which involves high temperatures and pressures. Contact metamorphism takes place at margin of an intrusive body of magma.

Interior of the Earth

The earth consists of four concentric shells, which are separated by three discontinuities. At these boundaries, earthquake waves changes in speed and direction. These four shells of the earth are called the crust, the mantle, the outer core, and the inner core. They differ in state or condition, in composition, in density, and in elasticity. The degree of elasticity is factor that determines the speed of earthquake.

            The crust extends down to the Mohorovieie (M-) discontinuity (or Moho) and includes the continents (which consist mostly of granite) and the ocean basins which consist mostly of basalt. Only the outer part of crust is visible; deeper rocks may become exposed by uplift, erosion, or may be brought to the surface by volcanism

            The continent and ocean basins are more or less in balance with another. This tendency toward equilibrium is termed isostasy. The continents stand higher than the ocean basins because they are lighter. Both the heavy and the light columns of rock, however, are in balance at an unknown depth called the level of compensation.

            Below the crust is the mantle. It consists of two or three zones of rock that are under considerable pressure, which keeps the rock from the melting at the high temperature that exists there. The bottom of the mantle is marked by the Wiechert-Gutenberg discontinuity, 1,800 mile down.

The outer core is 1,360 mile thick. In spite of increased pressure at this depth, the temperature is high enough to keep this zone in a molten state. The composition is believed to be largely iron, perhaps like that of iron-nickel meteorites.

The inner core extends 790 miles to the center of the earth, where its specific gravity may be more than 17. The enormous pressure (perhaps 3 million times that at the surface) keeps this zone solid in spite of the high temperature.

            Zoning of the earth is one of the major that must be accounted for by any acceptable hypothesis of the origin of the earth (see Chap. 1).

EARTH QUAKES

          Earthquakes are the result of movement within the earth. They in turn produce effect at the surface that may be disastrous to man and his buildings.     The most general accepted theory of earthquakes (seismic) activity is the rupture of rock by faulting.

          Shock waves are released by an earthquake at the underground site of the faulting, which is called focus. Earthquakes are classified as shallow, intermediate, and deep. The nearest place on the surface is the epicenter.

          Three main types of earthquake wave are known, although these wave types generate many other kinds as they travel through the earth and interact with one another and with the rock boundaries (discontinuities). P waves are compressing wave that move through the earth’s interior from the point of origin. S waves are shear wave that also go through the body of the earth from the point of origin.           L waves are surface waves that begin near the ground and travel just below it.

          The instrument that records earthquakes is a seismograph. A seismogram  is the permanent record that is produced.

          The intensity of an earthquake is determined by the amount of damage done. The actual energy released by an earthquake is measured as a magnitude.

          Although an earthquake may happen anywhere in the world, most of those that now occur are concentrated around the pacific Ocean and the Mediterranean Sea, across central Asia, down the Mid-Atlantic Ridge, and in separate areas    in eastern Africa and eastern Asia.

          Tsunamis are so-called tidal waves, but they are due to earthquakes, usually originating at the bottom of the ocean. They may travel more than 600 miles              an hour across the open sea, piling up when they reach a shallow shoreline.                                                                                               

WEATHERING

        Rock at or near the surface is slowly attacked by the atmosphere, by groundwater, and by organism. The rock is broken down physically and altered chemically. Soil is the most important product of this weathering, and particles of rock are set loose for gravity to act upon them.

Weathering is divided into two types: physical or mechanical weathering (disintegration) and chemical weathering ( decomposition ) These takes place together, but usually one is more prominent than the other, depending on the climate and the kind of rock.

Air is composed of nitrogen, oxygen, argon and other essential gases, plus varying amount of carbon dioxide and moisture.

Differential weathering is the diverse effect of weathering on rock. It acts differently on various natural cements that hold sedimentary rocks together, as well as on unlike part of the solid bodies themselves. Various areas of a rock may weather to different degrees, often producing a hollowed or patchy effect.

Soil is mixture of broken rock, decomposed rock, and decaying plant matter called humus.

Soil helps to prevent erosion by controlling drainage. The effect of gravity acting on loosened rock may produce a number of kinds of down slope   movement also called mass wasting. Even solid rock moves slowly but inevitably under the influence of gravity.