Category: Geography Notes PPT

We have all seen the eruption of volcanoes on television or computers. With the eruption of the volcanoes, lava starts flowing on the surface. Magma is usually a molten rock liquid that is found below the surface when the crust of the earth melts. The formation of igneous rocks starts taking place when the molten lava or magma begins to cool down and solidify. Igneous rock meaning relates to the solidification process that leads to the creation of rocks. The features of the igneous rock can be identified by its texture, mineral composition, density, and colour. These rocks are formed either with or without crystallization. 

Cooling Process of Igneous Rock

In the intrusive igneous rock, the process of cooling is usually slow that allows the growth of large mineral crystals within the rocks. The feature of igneous rocks having coarse minerals is due to the crystals of the intrusive rocks. Examples of igneous rocks include granite, peridotite, diorite, and gabbro. 

Next comes the extrusive type of igneous rocks that don’t allow crystallisation to take place. Thus, the final appearance is the fine-grained, glassy and vesicular rock formation. Examples of igneous rocks in the extrusive category include basalt, andesite, and rhyolite. 

Types of Igneous Rocks

The igneous rocks definition includes two categories of rock formation. These two types are discussed below in detail. 

Intrusive Igneous Rocks: When the molten lava cools slowly below the earth’s surface, the crystallization results in the formation of large crystals. These typically have a large amount of silica content within them and based on it they are known as diorite, gabbro, pegmatite, and granite. Actually, most of the magma available in the crust is never able to reach the earth’s surface. 

Extrusive Igneous Rocks: The extrusive igneous rocks are also known as volcanic rocks due to their formation from volcanoes. During the volcanic eruption when the magma reaches the earth’s surface, these are known as lava or volcanic rocks. The features of the igneous rocks in the extrusive category also have a silica content in a higher amount. Some of these rocks cool down so instantly that these form an amorphous glass. Examples of extrusive igneous rocks are basalt, pumice, tuff, etc. 

Types of Magma and Formation of Igneous Rocks

There are types of magma and these igneous rocks meaning comes from the type of magma they originate from. We will see the classification and properties of igneous rocks based on the magma. 

Intermediate Igneous Rocks: The composition of magma between felsic and mafic leads to the formation of intermediate igneous rocks. These are typically formed in the subduction zones that also include the oceanic plates. The structure of the rock includes examples like feldspar, pyroxene, biotite, quartz, and amphibole. 

Ultramafic Igneous Rocks: The characteristics of igneous rocks are mainly ferromagnesian and olivine in nature. For example, a slow cooking rock peridotite is a perfect example in this category. These igneous rocks cool down very slowly and are rare in nature. 

Mafic Igneous Rocks: When magma cools down, the ferromagnetic minerals dominate this type of rock formation. Typically, it is found prevalent in oceanic divergent zones. It contains minerals such as magnesium and iron silicate. Moreover, these rocks also have other minerals like olivine, pyroxene and others.

Felsic Igneous Rocks: This rock formation by magma contains aluminium and silicon. The formation takes place in the continental crust having high gas content. Besides, it also has mineral contents like biotite, quartz, potassium, and more. Examples of rock in this category include rhyolite and granite. 

Identification Process of Igneous Rocks

What we generally understand by the meaning of igneous rocks is that it is formed from the cooling and solidification of molten rocks or magma. When the molten lava starts to cool a new layer of minerals and textures are formed with the addition of new chemical components surrounding the rocks. The pressure and temperature at which the lava begins to cool and the time is taken depends on several factors. Due to this, we can see every igneous rock vary in its texture and composition. However, it is the textural and compositional properties that help us to identify the igneous rocks and determine the cooling process and magma formation. 

Did You Know

The first type of rocks formed on the earth surface was igneous rocks. These are also known as the primary rocks. 

Jadeite is a pyroxene mineral with the chemical formula NaAlSi₂O₆. It has a single axis. Depending on the composition, it has a Mohs hardness of 6.5 to 7.0. The mineral has a specific gravity of about 3.4.

The name jadeite is derived from the Spanish phrase “piedra de ijada,” which means “stone of the side”. The term nephrite is derived from the Latin version of the name, lapis nephriticus, which is a different mineral from the common name jade.

Jadeite Stone Chemistry

Other pyroxene end members that form solid solutions with jadeite include augite and diopside (CaMg-rich endmembers), aegirine (NaFe endmember), and kosmochlor (NaCr endmember). Omphacite is a type of pyroxene that contains both the jadeite and augite endmembers. Jadeite forms in metamorphic rocks under high pressure and relatively low temperature. Albite (NaAlSi₃O₈) is a common mineral in the Earth’s crust with a specific gravity of about 2.6, which is significantly lower than that of jadeite. Albite degrades under increasing pressure to form the high-pressure assemblage of jadeite and quartz.

Jadeitite refers to rocks that are almost entirely composed of jadeite. Jadeitite appears to have formed from subduction zone fluids in association with serpentinite in all well-documented occurrences. Jadeitite is resistant to weathering, and boulders of jadeitite formed in serpentine-rich environments can be found in a variety of environments.

Jadeite Stone Colour

The colour of jadeite typically ranges from white to pale apple green to deep jade green, but it can also be blue-green (as in the recently rediscovered “Olmec Blue” jade), pink, lavender, and a variety of other rare colours. Chloromelanite is a dark green to black mineral. The presence of trace elements such as chromium and iron has a large impact on colour. Its transparency ranges from opaque to nearly clear. Colour and translucency variations are common even within a single specimen.

Where is Jadeite Found?

Jadeite has been found in California, the United States, Myanmar, New Zealand, Guatemala, and Itoigawa, Japan; other jadeite locations include Kazakhstan, Russia, British Columbia, Canada, Italy, and Turkestan.

What is Imperial Jade?

Originally, it was assumed that all jade objects were made of the same material. However, in 1863, a Frenchman named Alexis Damour discovered that “jade” could be separated into two minerals: jadeite(imperial Jade) and nephrite.

The mineral compositions of jadeite and nephrite are markedly different. Nephrite is a magnesium-rich amphibole, whereas jadeite is aluminium-rich pyroxene. However, in the eyes of the average person, the two minerals have very similar physical properties.

Physical Properties of Jadeite and Nephrite

What is Jadeite Used for?

Over 180 axe heads made from jadeitite quarried in northern Italy during the Neolithic era have been discovered across the British Isles. Due to the difficulty of working this material, all of the axe heads found are thought to be non-utilitarian and to have represented some form of currency or be the products of gift exchange.

Many jadeite beads and axe heads, as well as the remains of Neolithic jadeite workshops, have been discovered in Itoigawa, Japan. These beads and axes were traded throughout Japan and the Korean Peninsula and were made by the Itoigawa region’s oldest known jadeite-using culture.

Litharge is a kind of mineral that is mainly used to manufacture Lead Stabilizers, Lead glass, pottery, paints, inks, and enamels. This is Lead Mono-Oxide, reddish or yellowish and heavy, reddish, earthy, odourless, solid, and water-insoluble. The other common names of this chemical component are Lead Oxide, Yellow Oxide, Plumbous Oxide, and commonly Lead Monoxide. At times Litharge is also known by its name Lethargic.

Formation of Litharge

This chemical is a secondary mineral that is formed from the oxidation of the galena ores. The mineral is formed as encrustations and coatings that are formed with the internal crystalline structure of tetragonal. The chemical components of Litharge give it a soft and greasy texture that contains a very high-specific gravity ranging between 9.14-9.35. One can also prepare PbO by heating lead metal at an approx. The temperature of 600˚C.

The preparation setup includes a pumping air on the molten Lead that will cause the oxidized mineral to fall off the top into a container where it gets solidified in minutes. Esper S. Larsen Sr. originally established Litharge as a polymorph of massicot and was supposedly identified as a new mineral in 1917. 

Composition of Litharge Formula

Types of Litharge

Out of hundreds of inorganic and organic lead compounds, including carbonates, oxides, sulfates, silicates, chromates, and acetates, Litharge is the most important of all. Lead Monoxide or Litharge consists of roughly 93% of Lead and only 7 % of oxygen as per weight. The process in which it is made yields a very distinctive variation of the physical properties. This makes it available in many particle sizes and only two crystal forms. 

When blended with red Lead and other combination additives, it yields a paste-type material used in the storage of batteries. The highest purity litharge is widely used in various crucial things like TV picture tubes, glass production, computer display terminals, etc. Litharge of Gold is formed when Litharge is mixed with red Lead, and Litharge of silver is formed as a by-product when silver is separated from Lead. Also, there is a Litharge of Bismuth obtained as a result of the oxidation of Bismuth. The two industrial forms of Litharge are Granular Litharge and Litharge powder. Litharge for sale is available in these mentioned variants.

Uses of Litharge

The heavy yellow powder, a product of Lead monoxide, Litharge, has several benefits and uses in the industrial arena. Litharge is hugely used as a red paste material for the storage of batteries derived from a blend of Red Lead and Litharge with other additives. Besides that,

• The most superior quality Litharge is extensively used in the production of glass that includes the TV picture tube and computer video display terminals. This is because of Lead’s high shielding capacity that blocks harmful radiation. Commonly, the inner part of a light bulb is made up of leaded glass.

• Litharge has immense use in the manufacture of enamels and the production of frits.

• Also, in the finest crystal glassware, the Lead present in Litharge imparts strength and brilliance.

• Red Lead is also used in various explosives industries, ceramics, paints, and pigments. 

Historical Terminology of the Chemical Name of Litharge

The chemical name of Litharge has its origin from Latin Lithargyrus, which is derived from the combination of lithos (stone) + arguros (silver). As a matter of fact defines, Litharge meaning is the mineral residue after silver is refined. Litharge is a term that is also used as a synonym for red Lead and white Lead. 

The Properties of Litharge Formula are Provided in the Tabular Form:

Physical Properties of Litharge

The earliest illustrations, hence far unearthed, that are indisputably portrayals of land characteristics are the Babylon or Babylonian tablets; certain land drawings found in Egypt and paintings found in early tombs. It is highly possible that these two civilizations evolved their mapping skills roughly simultaneously and in similar directions. Both were crucially related to the fertile areas of their river valleys and thus doubtless made 4r explorations and plats momentarily settled communities were established. Later they structured plans for building of roads, canals, and temples—the correspondent of today’s engineering plans.

Tablet in Iraq

A tablet discovered in Iraq exhibits the Earth as a disk encompassed by water with Babylon as its centre. Apart from this illustration, dating from about 1000 BCE, there seem to have been rather some attempts by Egyptians and Babylonians to display the type and extent of the Earth as a whole. Their mapmaking has been preoccupied with more practical needs, such as the inception of boundaries. Not before the time of the Greek geographer-philosopher did postulation and conclusions as to the nature of the Earth start to take form.

Greek Maps and Geography

The Greeks were superlative among communities of the ancient world for their pursuit and evolution of geographic comprehension. The deficit arable land in their own area resulted in maritime exploration and the evolution of commerce and colonies. By 600 BCE Miletus, on the Aegean, had transformed as a centre of geographic comprehension, and also cosmographic speculation.

Hecataeus’ Map of the World

Hecataeus, a scholar of Miletus, possibly generated the first book on geography in around 500 BCE. A generation afterwards of Herodotus, from more widespread studies and wider travels, stretched upon it. A historian accompanied by geographic leanings, Herodotus documented, among other things, an early orbit of the African continent by Phoenicians. He also enhanced upon the representation of the shape and degree of the then-known areas of the world, and he announced the Caspian to be an inland sea, combating the prevailing view that it was part of the “northern oceans”.

Herodotus’ Map of the World

Although Hecataeus has been considered the Earth as a flat disk encompassed by ocean, Herodotus and his followers cross-questioned the concept and lodged a number of other possible forms. As a matter of fact, the scholars and philosophers of the time seem to have been preoccupied for many years with analysis on the nature and extent of the world. Some modern scholars contributed the first hypothesis of a spherical Earth and the idea steadily developed into a consensus over many years. By the mid-4th century, the theory of a spherical Earth was well accepted among Greek scholars, and formulated six arguments to prove that the Earth was, in reality, a sphere. Subsequently after, the idea of a spherical Earth was usually accepted among geographers and other entities of science.

A disciple of Aristotle in about 300 BCE Dicaearchus, had put an orientation line on the world map, running east and west through Rhodes and Gibraltar. Eratosthenes, Ptolemy and Marinus of Tyre, progressively created the reference-line postulation until a reasonably all-inclusive system of meridians and parallels, as well as techniques of projecting them, had been achieved.

Claudius Ptolemaeus Maps and Geography in the Ancient World

Claudius Ptolemaeus (90–168 CE) has been the greatest figure of the ancient world in the advancement of geography and cartography. An astronomer, spent many years surveying the greatest repository of scientific knowledge at the library in Alexandria. His commemorating work, the Guide to Geography was produced in eight volumes.

The eighth volume was amongst the key contributions, consisting of instructions for creating maps of the world and discussions on mathematical geography and other basic principles of cartography. Ptolemy’s map of the world as it was then known marked the summit of Greek cartography and also the compendium of gathered knowledge of the Earth’s features at that time.

Mohorovicic discontinuity, also known as moho discontinuity is the boundary between Earth’s Crust and its Mantle. The moho lies at the depth of 30-50 km below the continents and 5-10 km below the sea level in the ocean. It is defined by the discontinuous changes in the velocity of seismological waves as they pass through the densities of rock. The moho lies almost entirely within the lithosphere.

Named after the pioneering Croatian Seismologist Andrija Mohorovicic, the moho divides both the oceanic crust and continental crust from the underlying mantle. The Mohorovicic discontinuity was first introduced in 1990 by Mohorovicic, when he observed that seismograph from shallow focus earthquakes has 2 sets of P waves and S- waves, one that followed a direct path near the Earth’s surface and another refracted by the high velocity medium. 

What is Moho Discontinuity?

The ‘Moho Discontinuity’ is the boundary between the crust and mantle. It has been named so as it was discovered by Croatian Seismologist Andrija Mohorovicic. This boundary marks a change in the seismic waves velocity from the crust to the uppermost mantle within the lithospheric plate. 

Who Discovered Moho Discontinuity?

Croatian Seismologist Andrija Mohorovicic is first credited with discovering and defining the Moho.  In 1990, the Mohorovicic observed the data from a local earthquake in Zagreb where he observed two different sets of P waves and Q waves propagating out from the focus of the earthquake. Mohorovivis knew that the waves caused by earthquakes travelling at velocities are proportional to the density of the material carrying them. On account of this information, he theorized that the second set of waves could only be caused by a sharp transition in density in the Earth crust, which could account for such a drastic change in the eave velocity. Using the velocity data from the earthquake, Mohorovicic was able to calculate the depth of the Moho to be approximately 54 km, which was backed up by subsequent seismological studies.      

             

How Deep is the Moho Discontinuity?

The Moho discontinuity marks the lower limit of the Earth crust. The Moho discontinuity is 5-10 kilometres (3-6) mi below the ocean base and 20 – 90 kilometres (10 – 60) mi below the continental surface with an average of 35 kilometres (22 mi). Mohorovicis further used his discovery to study thickness variations of the crust which has a relatively uniform thickness, while continental thickness is thickest under the mountain ranges and thinner under the plains. 

Moho Role

Moho has played a large role in the field of geology and Earth Science well for a century.  By observing the Moho reflective nature, and how it affects the speed of W waves, scientists were able to hypothesize about Earth’s composition. This study gave rise to Earth seismology.

The Project Mohale in the 1960s attempted to drill to the Moho from deep – ocean regions.  After an initial success in establishing deep ocean drilling, the project underwent political and scientific opposition, mismanagement, cost overturn, and it was cancelled in 1966.

Did You Know?

• Moho discontinuity is defined as the boundary between Earth’s crust and the mantle, observed by a sharp increase in the velocity of the seismic waves passing through the Earth.

• The name Mohorovicic discontinuity was received from Croatian geophysicist Andrija Mohorovičič, in 1909.

• As per the recent studies, the moho is now realised as a transition zone rather than a sharp discontinuity.

Oceanic ridge is a continuous submarine chain of mountains that extends roughly 80,000 km (that is 50,000 miles) among all the oceans present in the world. In the ocean basin, these ocean ridges are the largest features. Geographically speaking, these oceanic ridges are the most distinct and prominent feature on the surface of the earth after the continents and oceans being the prominent ones. 

Previously these features were also referred to as the mid-ocean ridges. While the largest ocean ridge, the East Pacific Rise is quite a distance from a mid-ocean location, hence, we can say that the generalization is not exactly correct. Further, students must not confuse these oceanic ridges with aseismic ridges, which originated apart from these.  

Mid Ocean Range

A mid-ocean ridge also known as the mid-oceanic ridge is an underwater mountain range, which is formed by the action of plate tectonics. There is uplifting of the ocean floor, which is caused due to the convection currents as it rises in the mantle which is beneath the oceanic crust and here it creates magma. The creation of magma is done where the two tectonic plates meet at a divergent boundary.

These mid-ocean ridges of the world are all connected and they form a single global mid-oceanic ridge system which is a part of every ocean that makes up the mid-oceanic ridge system. Here the longest mountain range in the world is about 60,000 km in length.

There are two processes involved in this, one is ridge-push and the other is slab-pull, they are responsible for the spreading seen at the mid-ocean ridges, while there is some uncertainty about the fact which is dominant.

Mid Atlantic Ridge

The Mid-Atlantic Ridge abbreviated as MAR is the mid-oceanic ridge which is divergent or is constructive with a plate boundary that is located along the Atlantic Ocean floor. Also, this serves to be the longest mountain range in the world. The Mid-Atlantic Ridge separates North America from the Eurasian and African Plate; this happens in the North Atlantic. Also, this ridge separates North America from Azores Triple Junction. While, in the South of Atlantic, the ridge separates the African and the South American plates. The ridge further extends from a place in the Gakkel Ridge which is called the Mid-Arctic Ridge to the northeast in Greenland, proceeding southward to Bouvet Triple Junction in the Southern part of the Atlantic. 

We know that the Mid-Atlantic Ridge is majorly an underwater feature, while portions of it have elevation to the extent above the sea level, for example in Iceland. 

Submarine Ridge

Submarine Ridge is quite elongated and steep-sided elevation of the ocean and the sea floors. The Submarine ridges extend up to hundreds and thousands of kilometers, lengthwise and the width is about several hundred km. Here the peaks often rise above sea level to form many such islands. 

In the submarine continental margins, the submarine ridges are very rare, while their structure being analogous to the structure of those of the mountains which are located on the adjacent parts of these continents. In the transition zone, the submarine ridges appear mainly like the island arcs.

On the ocean floor, the submarine ridges may be block, or block-folding, or like the volcanic ridges.  The mid-ocean ridges are the largest submarine ridge. 

Indian Ocean Ridge

Talking about the Indian Ocean Ridge, the Carlsberg Ridge which is also a submarine ridge of the Arabian Sea and the Indian Ocean is a prominent feature. This ridge is a portion of the Mid-Indian Ridge and this extends from the vicinity of Rodrigues Island to the Gulf of Aden, basically, this means northwest to southeast. This ridge separates the Arabian Sea located in the northeast from the Somali Basin in the southwest.

East Pacific Rise

The East Pacific Rise is also a mid-oceanic ridge which has a divergent tectonic plate with a boundary that is located along the Pacific Ocean floor. This separates the Pacific Plate in the west from the North American Plate, from the Rivera Plate, from the Cocos Plate, the Nazca Plate and also from the Antarctic Plate. This runs southward from the Gulf of California which is in the Salton Sea basin, South California to a point near 55° S, 130° W, then it joins the Pacific-Antarctic ridge.