Category: Geography Notes PPT

The amphibole mineral is a mineral belonging to the inosilicate classification of minerals. They are known for and classified as such because of their structural configuration that leads to the formation of a prism or needle-like structures. The amphibole is made up of double-chain silica (SiO4) tetrahedra. In these tetrahedra, the two chains of silica are linked with one another at the vertices and typically contain ions of iron and/or magnesium in their structures. The Amphibole group of minerals is a supergroup according to the International Mineralogical Association as there are two more groups and several subgroups classified within it. 

Naming of Amphibole

The amphibole meaning is derived from the ancient Greek language from the root word amphibolos. The term amphibolos means “double entendre” i.e. ambiguousness. Deriving amphibole meaning from the amphibolos term, the mineral amphibole was first used by René Just Haüy. With this nomenclature tremolite, actinolite and hornblende. Because of the composition and appearance of these minerals, these particular minerals were named amphibole meaning something that is showing dual and ambiguous properties. 

Physical Properties of Amphibole

The following are the physical properties and chemical characteristics of the amphibole mineral:

• Amphibole is made up of double chains of silica in a tetrahedral structure with both the chains being linked to each other at their vertices.

• The crystalline structure of the amphibole contains ions of iron and/or magnesium within it.

• The amphibole mineral can be found in different colors such as green, black, white, yellow, brown or some of its forms can be colorless as well.

• The amphibole structure is known for the formation of two different types of crystals. The two types of crystals formed are either prismatic or needle-like in shape.

• The amphibole chemical composition is essentially made up of hydroxyl or halogen groups within their crystal structure.

• Although, there are similarities in-between certain properties of pyroxene and amphibole, the basic structure of the amphibole crystal is different from the pyroxene crystal as the pyroxene crystal is made up of a single chain of silicates and the amphibole is made up of double chains of silica.

• Amphiboles form cleavage planes at around 120 degrees which is different from the pyroxenes as pyroxenes form the cleavage planes around 90 degrees.

• The objects classified in the amphibole mineral group are also specifically less dense than the corresponding objects that belong to the pyroxene category.

• Optically as well the properties of amphiboles are interesting because optically the amphiboles due to their unique amphibole structure display different colors when viewed or observed from different angles. They have a very strong pleochroism characteristic and a smaller angle of extinction on the plane of symmetry.

Characteristics of Amphibole

The minerals of the amphiboles can originate from either the igneous or metamorphic origin. The common forms of amphibole are present in both the intermediate to felsic igneous rocks rather than mafic igneous rocks because of the iron or magnesium ion content. The characteristics of amphibole found in the rocks and determined by the formation are given as follows:

• The property of the amphibole structure to have double silica chains because of the higher silica content and higher dissolved water content found in the more evolved magmas. These are the conditions that favor the formation of amphiboles over the formation of pyroxenes.

• Amphiboles are primary constituents of the amphibolites which also include actinolite, hornblende, plagioclase, etc.

• Andesites are the ones that contain the highest amount of amphiboles that is 20% of the total composition.

• Another one of the minerals included in the amphibole is the hornblende and is widespread in the igneous and metamorphic rocks and more prominently in the syenites and diorites. 

• The naturally occurring amphibole sometimes contains calcium as the main constituent. 

• The amphiboles formed include the metamorphic rocks the ones developed in limestones by the contact metamorphism and also the ones formed by the alteration of other ferromagnesian minerals like the hornblende which is a product of the pyroxene. After pyroxene, the pseudomorphs of amphibole are known as the uralite.  

• The amphibole formula that is found commonly in the representation of the minerals classified under it is RSi4O11 where R is the specific group present in different minerals.

• Most common of the minerals among is the amphibole asbestos. Four such minerals are commonly known as amphibole asbestos. Those four are anthophyllite, riebeckite, cummingtonite/grunerite asbestos series and tremolite/actinolite asbestos series. The cummingtonite/grunerite are generally known as brown or amosite asbestos, whereas, the riebeckite mineral is known as blue asbestos. All of these are very commonly known as amphibole asbestos.

Use of Amphibole

The amphibole mineral finds its utility for a variety of purposes. Because of its coloring and the ability to exhibit different colors when being viewed from different angles, one of the most prominent uses of amphibole is in decorations. It can be simply shaped as desirable and then kept in the house as a decorative or interior designing item. Some of the observable uses are as paving stones, and as veneers or facings on the buildings. Another one of the uses of amphibole mineral includes its utility as crushed stone for activities such as road construction and railroad bed construction. This is vastly done near the sites where amphobiles are a common occurrence.

General contemplations

Amphiboles are tracked down chiefly in transformative and volcanic rocks; they happen in numerous transformative rocks, particularly those obtained from mafic volcanic rocks (those containing dim hued ferromagnesian minerals) and siliceous dolomites. Amphiboles likewise are significant constituents in an assortment of plutonic and volcanic molten rocks that reach in arrangement from granitic to gabbroic. Amphibole, from the Greek amphibolos, signifying “equivocal,” was named by the popular French crystallographer and mineralogist René-Just Haüy (1801) in reference to the extraordinary assortment of creation and appearance shown by this mineral gathering. There are 5 significant gatherings of amphibole prompting 76 synthetically characterized end-part amphibole pieces as per the British mineralogist Bernard E. Leake. As a result of the wide scope of synthetic replacements allowable in the precious stone design, amphiboles can solidify in volcanic and transformative rocks with a wide scope of mass sciences. Normally amphiboles structure as long kaleidoscopic gems, emanating splashes, and asbestiform (sinewy) totals; in any case, without the guide of compound investigation, it is hard to megascopically distinguish everything except a couple of the more unmistakable end-part amphiboles. The mix of kaleidoscopic structure and two precious stone-formed headings of cleavage at around 56° and 124° is the demonstrative component of most individuals from the amphibole bunch.

Compound structure

The perplexing compound piece of individuals from the amphibole gathering can be communicated by the overall recipe A_0–1B₂C₅T₈O₂₂(OH, F, Cl)₂, where A = Na, K; B = Na, Zn, Li, Ca, Mn, Fe²⁺, Mg; C = Mg, Fe²⁺, Mn, Al, Fe³⁺, Ti, Zn, Cr; and T = Si, Al, Ti. Almost complete replacement might occur among sodium and calcium and among magnesium, ferrous iron, and manganese (Mn). There is restricted replacement between ferric iron and aluminum and among titanium and other C-type cations. Aluminum can to some extent substitute for silicon in the tetrahedral (T) site. Halfway replacement of fluorine (F), chlorine, and oxygen for hydroxyl (OH) in the hydroxyl site is additionally normal. The intricacy of the amphibole equation has led to various mineral names inside the amphibole bunch. In 1997 Leake introduced an exact classification of 76 names that include the compound variety inside this gathering. The mineral classification of the amphiboles is partitioned into four head regions dependent on B-bunch cation inhabitants:

(1) The iron-magnesium-manganese amphibole bunch,

(2) The calcic amphibole bunch,

(3) The sodic-calcic amphibole bunch,

(4) The sodic amphibole bunch.

Actual properties

Long kaleidoscopic, acicular, or sinewy gem propensity, Mohs hardness somewhere in the range of 5 and 6, and two bearings of cleavage converging at around 56° and 124° for the most part do the trick to recognize amphiboles close by examples. The particular gravity upsides of amphiboles range from around 2.9 to 3.6. Amphiboles yield water when warmed in a shut cylinder and wire with trouble in a fire. Their shading goes widely from dry to white, green, brown, dark, blue, or lavender and is connected with the arrangement, primarily the iron substance. Magnesium-rich amphiboles like anthophyllite, cummingtonite, and tremolite are luster or light in shading. The tremolite-ferro actinolite series goes from white to dull green with expanding iron substance. The finely stringy and enormous assortment of actinolite-tremolite known as nephrite jade reaches from green to dark. Normal hornblende is ordinarily dark. Glaucophane and riebeckite are typically blue. Anthophyllite is dim to different shades of green and brown. The cummingtonite-grunerite series happens in different shades of light brown. Sans iron assortments of tremolite containing manganese can have a lavender tone.

The name is “Mako Sica,” which means “land bad.” This Badland National Park is located in the southwestern part of South Dakota. This National Park consists of approximately 244,000 acres of sharply eroded buttes, pinnacles and spires which are being blended with the protected mixed-grass prairie in the United States. This site is desolation at its best, with bare eyes, one cannot find any sort of civilization in this area. and see no sign of civilization.

The land is being ruthlessly ravaged by wind and by water, thus it became picturesque. The Badlands quenches the thirst of wonderland of the bizarre, the colourful spires and pinnacles, with its massive buttes and deep gorges add more to the beauty.

The erosion of these Badlands has revealed layers of sedimentary rocks of different colours, ranging from purple and yellow to tan and grey. The colours red and orange (which is because of the iron oxides) and white (for the volcanic ash) sparks natural beauty in this Badland National Park.

Badland

Badlands are actually a type of drier terrain where there are softer sedimentary rocks. The softer sedimentary rocks are also coupled with clay-rich soils which have extensively faced erosion by the wind and water. Badlands are being characterized by steep slopes, with a lack of vegetation. Features common in Badlands are – Canyons, gullies, ravines, buttes, hoodoos and other geological forms which are quite common in these areas. These features are often difficult to identify and navigate by foot. Generally, Badlands have a spectacular colour to display. The colour ranges from dark black/blue coal stria to bright clays to red scoria.   

Inquisitive enough, how did these remarkable features get their origin? By the process of deposition and erosion, Badlands are being formed naturally. The process of deposition marks the accumulation, over the time period, of the layers of mineral in the material. Different environments like seas, rivers, or tropical zones, deposit varied sorts of clays, silts, and sand. For example, the Badlands formations in the Badlands National Park in South Dakota have undergone a 47-million-year period of deposition, they have spanned three major geologic periods that is the – Cretaceous Period, Late Eocene and the Oligocene Period. This resulted in the clear, distinct layers of sediment being served as a dramatic display.  

Borrego Badlands

These Badlands measure twenty miles wide by another fifteen miles long, into the stark, arid landscape of the Borrego Badlands which stretched across the portion of the enormous Anza-Borrego State Park, located in California’s south-eastern corner. During the sunset and sunrise, the Badlands’ creased and wrinkled ridge structures cast bold shadows which stretches across a maze of the golden hills and the sand-coloured arroyos. Originally the whole view was shaped by water. The fossilized seashells were found in the region, this proves that it was once being submerged under the blend of salty tropical waters which is from the Gulf of California and the freshwater from the Colorado River. 

To enjoy the best view, the best places to get a look at these Badlands’ surreal scenes is from Font’s Point, which is commonly known as California’s Grand Canyon. This point is a popular spot for photographers, especially at the time of sunset or during full-moon nights.

Paria Badlands

The location of Paria Badlands is between Kanab, Utah and Page, which is in Arizona. This takes about an hour or so to fully see the view. They serve as an excellent side trip while heading towards or from any hikes.  

While there is no hiking trail at the Paria Badlands. The structure is a way to wind down from some other hikes in the surrounding areas. Here no hiking is required. The views enjoyed here are pretty impressive and there are scenic views from a couple of steps outside your car. 

How do We Get There?

From Kanab, Utah, you need to take US-89 east, after driving approximately 32.5 miles. There will be a sign which will read “Old Pahreah Townsite.” After which turn left into the large, round gravel parking area, here you will see some plaques and other large stone landmarks. If coming from the Page, Arizona, then take US-89, then drive for 40.5 miles. Here, you will see a sign for “Old Pahreah Townsite.” Then turn right here into this gravel parking area where you will find the plaques and landmarks. 

They basically talk about the history of the area. After you read the plaques head north on the dirt road for about 4.8 miles, then you will come to the best spot for pictures in the Paria Badlands. This same road will eventually then lead you to the Old Paria cemetery which consists of about 20 graves. Near this cemetery area and the parking area, on the south side of the Paria River, there was the old movie set where many several films were being shot from the 1940s through the 1970s. 

Let’s talk about the Halide mineral before we get into Carnallite. Any of a group of naturally occurring inorganic compounds that are salts of the halogen acids is known as a halide mineral (e.g., hydrochloric acid). With the notable exceptions of halite (rock salt), sylvite, and fluorite, such compounds are uncommon and only found in small quantities. The simple halides, halide complexes, and oxyhydroxy-halides are known as three broad groups of halide minerals in terms of composition and structure. These categories are also distinguishable in terms of their modes of occurrence.

Alkali salts, alkaline earth, and transition metals are examples of basic halides. The transition-metal halides are unstable when exposed to air and are soluble in water. The most well-known evaporite mineral is halite, sodium chloride (NaCl); it is found in large beds with other evaporite minerals as a result of the deposition of brines and trapped oceanic water in impermeable basins and their evaporation. Sylvite, potassium chloride (KCl), is also present in small quantities in such beds. Among the simple halides, a few double salts such as carnallite and tachyhydrite formed under conditions close to the formation of halite. Carnallite is also a halide mineral.

Carnallite

Carnallite is a soft, white halide mineral that contains hydrated potassium and magnesium chloride and is used to make fertilisers. Carnallite is found in the upper layers of marine salt deposits, where it tends to be an alteration result of pre-existing salts, along with other chloride minerals. The mineral can be found mostly in salt deposits in northern Germany, as well as in Spain, Tunisia, and the southwestern United States.

Carnallite Formula

Chemical Formula of Carnallite is KMgCl₃·6(H₂O). Slow crystallisation at 25°C will yield synthetic carnallite crystal specimens from 1.5 mole percent KCl and 98.5 mole percent MgCl₂·6H₂O. It has a density of 1.602 g/cm³. Grinding a mixture of hydrated magnesium chloride and potassium chloride can also yield carnallite.

Structure of Carnallite

We discussed the Chemical Formula of Carnallite. Now let’s look in detail about the Structure of Carnallite. 

• Carnallite basic structure has corner- and face-sharing. A network of KCl₆ octahedra exists, with two-thirds of them having the same faces.

• The open spaces within the KCl octahedra are occupied by Mg(H₂O)₆ octahedra.

• The interatomic distance between Mg and H₂O varies between 0.204 and 0.209 nanometers, with an average of 0.2045 nanometers. 

• K and Cl have an interatomic distance of 0.317 to 0.331 nm, with an average of 0.324 nm.

• The estimated density of the resulting structure is 1.587 g/cm³, which is very similar to the measured value of 1.602 g/cm³.

Structure of Carnallite [Carnallite Formula is KMgCl3·6(H2O)]

According to the third of Pauling’s law, sharing one’s face increases the chances of instability. The magnesium ions are encased in water molecules in carnallite. The water molecules serve as charge transmitters, preventing the magnesium and chloride from interacting directly. Each of the five chloride anions is paired with two potassium cations and four water molecules. This means that each of the two potassium ions gives each chloride anion 1/6 of a +1 charge. Each of the four water molecules gives the chloride 1/6 of a +1 charge. The charges add up to six 1/6 positive charges, which offset the chloride’s negative charge. Because of these two factors, the rare face sharing mentioned in Pauling’s second and third rules is appropriate in the carnallite structure.

Physical Properties of Carnallite

The refractive index of carnallite varies from 1.467 to 1.494. Hematite (Fe₂O₃) inclusions in carnallite can cause it to be red. In the thin laminae of hematite, broken shards of iron oxide create red tints. In high humidity, carnallite also deliquesces. This indicates that it is highly soluble in water. Individual crystals are tabular and pseudo-hexagonal, but they are exceedingly uncommon. The forming environment, the lack of cleavage, and fracture are all field indicators of carnallite. Other factors to consider include density, taste, associations with local minerals, and luminescence. Carnallite has a sour flavour. Carnallite has the potential to be both fluorescent and phosphorescent. The potassium in carnallite readily fuses in a blaze, resulting in a violet hue. Carnallite can be distinguished from other evaporate minerals very easily. It has a bitter taste and, unlike halite, no cleavage. Carnallite has a specific gravity of just 1.6 and, unlike kieserite and other non-potassium salts, produces a violet flame when placed in a gas flame. Environment of formation, lack of cleavage, associations, density, deliquescence, fracture, and taste are the best Field Indicators.

Geologic Occurrence

Halite, anhydrite, dolomite, gypsum, kainite, kieserite, polyhalite, and sylvite are examples of mineral associations dependent on physical properties. Evaporites are mineral sediments that contain carnallite minerals. Evaporation of seawater concentrates evaporites. The water inflow must be less than the evaporation or usage levels. This results in a longer evaporation period. When 10%–20% of the original water sample remains after controlled environment experiments, the halides shape. Sylvite makes up about 10% of the total, followed by Carnallite. Carnallite is mainly present in marine deposits that are saline.

Uses

Carnallite is a mineral that is often used in fertilisers. It is a significant potash source. Only sylvite is more important in potash production than carnallite. They’re both rare because they’re among the last evaporites to form. The primary sources of fertiliser are soluble potassium salts. This is due to the difficulty of separating potassium from insoluble potassium feldspar. Carnallite is a minor magnesium source found all over the world. 

Conclusion

Carnallite is a valuable fertiliser since it contains a lot of potash. Potash is mostly obtained from sylvite, but carnallite also contributes significantly. The magnesium production of carnallite is much less important globally, but it is still Russia’s most important source. Potassium is a common element, but it is unfortunately wrapped up in insoluble silicate minerals like potassium feldspars. Since potassium must be in a soluble state to be effective as a fertiliser, soluble potassium salts are the preferred source. Evaporite minerals like carnallite and sylvite, for example, are some of the last minerals to evaporate from sea water, making them difficult to form. In approximately that order, minerals including calcite, dolomite, gypsum, anhydrite, and halite crystallise first. The conditions required for potassium and magnesium salts to form include seawater contained in a cut-off, but not fully isolated basin, similar to the Black Sea. The Black Sea, on the other hand, does not form carnallite because it does not have a warm enough environment to allow for intensive evaporation (this is an evaporite mineral after all). The concentrated brine must not be allowed to leave the basin in order for the salinity to continue to rise. The brine will fall to the basin’s bottom, allowing fresher water to join, bringing more magnesium into the basin. This has the effect of delaying the crystallisation of the salts and increasing the brine’s salinity. If evaporation does not continue in this direction, the minerals mentioned above will fill the basin before the potassium salts crystallise.

India shows a wide variation in the climatic conditions ranging from snowfall in the Himalayan arch to burning heat in the south. The Himalayas and the Thar Desert have a great influence on the overall climatic conditions of the country. The Indian subcontinent is warmer than the other areas of the same altitude because the Himalayan Mountains block the central Asian katabatic winds. On the other hand, the Thar Desert attracts the southwest summer monsoon winds that are moist and provide the required rainfall in the months from June to October. There are four principal weather and climate of India, winter, summer, monsoon, and post-monsoon.

 

What are the Factors Affecting the Climate of India?

1. Location

The Indian subcontinent stretches from 8°N to 37°N and is located to the north of the equator. Tropic of Cancer passes over the center of the country hence the southern areas are closer to the equator and experience higher temperatures. While the northern parts of the country experience lower temperatures comparatively. The temperatures are quite low during the winters. The presence of the Arabian Sea and the Bay of Bengal, cause the right and left coasts of the country to be humid and mild. The Indian subcontinent is located north of the equator and stretches from 8°N to 37°N. Because the Tropic of Cancer passes through the center of the country, the southern areas are closer to the equator and have higher temperatures. The northern parts of the country, on the other hand, have lower temperatures. During the winter, temperatures are quite low. Because of the presence of the Arabian Sea and the Bay of Bengal, the country’s right and left coasts are humid and mild.

2. Span from the Sea

The closer the regions are to the sea, the more humid is the climate. They experience moderate summers and mild winters. However, areas situated far away from the coastline, don’t have any influence on the huge water body and hence experience extreme climatic conditions. Delhi for example has an annual temperature of 20° C whereas Kochi has about an average temperature of about  30°C. The climate becomes more humid as one gets closer to the sea. Summers are pleasant, and winters are mild. However, areas located far from the coastline do not influence the vast body of water and thus experience extreme climatic conditions. For example, Delhi has an annual temperature of 20° C, whereas Kochi has an average temperature of around 30° C.

3. The Himalayan Mountains

These mountains are a climatic divider between Central Asia and the Indian subcontinent. They do not allow the cold Central Asian winds to enter the continent, hence keeping it warmer than other regions. They also block south-west monsoon winds from entering the country’s atmosphere. These mountains serve as a climatic barrier between Central Asia and India. They prevent cold Central Asian winds from entering the continent, keeping it warmer than other regions. They also keep the southwest monsoon winds out of the country’s atmosphere.

4. Pressure and Winds 

India has northeasterly winds flowing from the subtropical high-pressure belt of North towards the equatorial low-pressure areas. These winds carry very little moisture since they flow only over land. Hence they do not bring any rain to the county. On the other hand, during winters, from the high-pressure region of the northern Himalayas, cold dry winds flow into the continent towards the South. In summers this reverses and low pressure is created in interior Asia. Hence the southwest monsoon winds are originated and because these winds flow over the warm oceans they collect moisture and bring the majority of rainfall in the country. Northeasterly winds blow across India from the subtropical high-pressure belt to the equatorial low-pressure areas. Because they only blow over the land, these winds carry very little moisture. As a result, they do not bring rain to the county. During the winter, however, cold dry winds from the high-pressure region of the northern Himalayas flow into the continent from the south. This is reversed in the summer, resulting in low pressure in the interior of Asia. As a result, the southwest monsoon winds are formed, and because these winds blow over warm oceans, they collect moisture and bring the majority of the country’s rainfall.

 

What do you mean by Climatic Controls? 

The factors that influence or control the contrast of weather in a particular region are called climatic controls. Climate controls are the factors that influence or control the contrast of weather in a specific region.

 

The following are India’s climate controls-

• The dominant temperature of the region is determined by the country’s geographical location on the latitude. Temperatures gradually decrease as we move from the equator to the poles, as we all know. Because the southern states are closer to the equator, they have higher temperatures, while the northern states have lower temperatures.

• Temperature variations are caused by altitude, just as they are by distance from the equator. As a result, higher altitude regions in India have cooler climatic conditions.

• The major factors that influence the climate of any region are pressure and winds. The northeasterly and southwest monsoon winds, for example, are responsible for the monsoon in India.

• The temperature of a region is determined by the ocean currents that flow over it; warmer ocean currents warm the region, while moist ocean currents cool it.

• The Himalayan Range is the country’s most important relief barrier. It restricts the inflow of Central Asian winds to the peninsula’s northern tip, keeping temperatures warmer than in other parts of Asia.

• The geographical location on the latitude of the country decides the dominant temperature of the region. As we know, the temperatures gradually reduce when we move from the equator to the poles. Since the southern states are located closer to the equator they have high temperatures and the northern states have comparatively lower temperatures. 

• Just like the distance from the equator causes variations in temperatures, the altitude also does. Hence regions at higher altitudes in India experience cooler climatic conditions. 

• Pressure and Wind are the major factors that influence the climate of any region. For example, the northeasterly winds and southwest monsoon winds are responsible for the monsoon in India.

• The ocean currents flowing over a region determine the Temperature of that region, warmer ocean currents make the region warmer, whereas moist ocean currents make it cooler. 

• The Himalayan Range is the most important relief barrier of the country. It restricts the inflow of Central Asian winds to the northern part of the peninsula,  hence keeping the temperatures warmer than other regions of Asia.

A coral reef is a marine ecosystem characterized by corals that create reefs. Reefs are made up of coral polyp colonies bound together by calcium carbonate. The majority of coral reefs are made up of stony corals, which have polyps that crowd together.

Shallow coral reefs, also known as sea rainforests, are home to some of the most diverse species on the planet. They cover less than 0.1 per cent of the world’s ocean surface or about half the size of France, but they are home to at least 25% of all marine animals, including fish, molluscs, worms, crustaceans, echinoderms, sponges, tunicates, and other cnidarians. Coral reefs thrive in nutrient-depleted coastal waters. Coral reefs are most often seen at deeper depths in tropical oceans, although deep water and cold water coral reefs can be found on smaller scales in other regions. Let us take a look at different types of reefs.

Types of Reefs

It is classified into three types of coral: fringing, barrier, and atoll.

1. Fringing Coral Reefs

2. Barrier Coral Reefs

3. Atoll Coral Reefs

Let us take a look at them in detail.

1. Fringing Coral Reefs: One of the three major types of coral reef is a fringing reef. It differs from the other major groups, barrier reefs and atolls, in that it has either a completely shallow backreef zone (lagoon) or none at all. If a fringing coral rises straight from the shoreline, the reef flat stretches all the way to the beach, with no backreef. This is the most widespread kind of coral reef found in the Caribbean and the Red Sea. In a long-term reef development pattern, fringing reefs, according to Charles Darwin, are the first kind of reefs to develop around a landmass.

2. Barrier Coral Reefs: Barrier reefs are isolated from the shores of a peninsula or island by a deep channel or lagoon.  Formal paraphrase They are similar to the later stages of a fringing reef with its lagoon, but they vary mostly in size and origin. Their lagoons can span many kilometres and range in depth from 30 to 70 meters. Over everything, the offshore outer reef edge formed in the open sea rather than along a shoreline. These reefs, including atolls, are thought to have evolved when the seabed lowered or the sea level rises. Barrier reefs are much rarer than fringing reefs and they take much longer to form.

3. Atoll Coral Reefs: It is a ring-shaped coral reef with a coral surface that partly or entirely encircles a lagoon. Around the bottom, there may be coral reefs or cays. The creation of an atoll reef is described by Charles Darwin’s subsidence model as the subsidence of a volcanic island around which a coral fringing reef has formed. The volcanic island became extinct and eroded over geologic time, eventually sinking entirely under the ocean’s crust. When the volcanic island subsides, the coral fringing reef separates from the island, becoming a barrier reef. There are around 440 coral atolls on the planet.

Zones of Coral Reefs

Coral reef environments are divided into zones that house various types of habitats. 

The three main areas are usually recognized: 

• Fore coral,

• Reef crest, and

• Back reef 

The three zones are connected both physically and ecologically. Oceanic cycles and reef life facilitate the exchange of seawater, sediments, nutrients, and aquatic life. The majority of coral reefs live in seas less than 50 meters deep. Some live on tropical continental shelves, such as the Great Barrier Reef, where cool, nutrient-rich upwelling does not occur. Others, such as the Maldives, are located in the deep ocean around islands or as atolls. Reefs form around islands as they sink into the water, and atolls form when an island sinks below the sea’s level.

Reproduction in Coral Reefs

Corals reproduce sexually as well as asexually. During the course of its life, a polyp can use all reproductive types. Internal or external fertilization is used by corals to replicate sexually. The reproductive cells are located on the mesenteries, which are membranes that radiate inward from the stomach cavity’s layer of tissue. Any mature adult corals are hermaphroditic, while others are either male or female. Only a few, change sexes as they mature.

Spawning happens like a mass orchestrated process along several reefs, where all coral species in an environment release their eggs and sperm at about the same time. Since male and female corals cannot come into reproductive interaction with each other, the timing of a broadcast spawning event is critical. Since colonies can be separated by large distances, this release must be specifically and widely timed, and it typically occurs in response to several environmental cues.

The less water that moves, the greater the chance of fertilization. The best time is in the spring. The release of eggs or planula is normally at night and is often in sync with the lunar cycle (three to six days after a full moon). The time between release and settlement is just a few days, but some planulae will float for several weeks.

Benefits of Coral Reefs

• Coral reefs shield coastlines from hurricanes and flooding, provide employment for local residents and provide recreational opportunities.

• They are source medicines and food. Reefs provide fuel, jobs, and security to over half a billion people.

• On and around beaches, fishing, swimming, and snorkelling generate hundreds of millions of dollars for local companies. The annual net economic value of the world’s coral reefs is estimated to be in the tens of billions of dollars.

Did You Know?

• Coral reefs make up a small percentage of the ocean – less than 1% – but they are home to about 25% of all aquatic animals on the planet. Coral reefs are home to over 4,000 different species of fish!

• Corals and algae have a symbiotic bond, so as the ocean temperature rises, corals remove their algae, causing them to white in colour and this process is bleaching and the coral is known as bleached coral. Many corals have been seen to emit bright colours in a vain effort to withstand rising ocean temperatures.

• The Great Barrier Reef is the largest coral reef which is the only animal structure visible from space, stretching for 2300 kilometres.

The economy of a country shows up its overall financial condition and denotes the country itself as an economic unit. There are various elements on which a country’s economy depends upon. Some of them are demography, infrastructure and natural resources, and the average lifestyle of the people This is the reason why geography is prominently related to a country’s economy. If you are at the school level, you have to know the economy of your country. The best way to know about the economy of the country is by going through the chapters and understanding the sources of finances. You can visit the site to get in-depth knowledge. 

Lifelines of National Economy

There are several factors on which the economy of a country can depend. Here is a shortlist with some details about the economical lifelines of any developing country in the world. 

1. Demography: 

The primary lifeline of a nation’s economy is demography. If the ratio of the working-class population and the scopes of jobs are in balance, you can expect the economy of a country is well balanced. 

2. Natural Resources: 

Several businesses depend on the abundance of some natural resources. A country with several natural resources might not have a weak economy. 

3. Population: 

Population is one of the lifelines of a country’s economy but an instance of overpopulation can be harmful in the same way. The economy can never be in equilibrium in an overpopulated country as the per head finances will never be constant. Overpopulation leads to unemployment which is one of the prominent curses for the economy. 

4. Infrastructure: 

Infrastructure plays a crucial role in maintaining a balance in the economy of a country. A country must have the proper infrastructure in the field of industries, agriculture,  transport, health, social service, defense, and entertainment to ensure that the economy remains at a satisfactory stage. 

5. Government Rules: 

In many leading countries, the ruling government plays a vital role as a determinant of the economic condition of the country. If the government of the country follows an administrative blueprint that is constructive, it can be the most secured economic lifeline for a country. In the same way, if the government is reluctant towards properly running the country, the economy of the country can crash. 

In a condition, the cash flow in the country can get hampered. Moreover, corruption can destroy the financial sector of the country.

Lifeline of Indian Economy: Details

Lifeline of the Indian economy is a chapter of CBSE class 10 Geography that contains the details of the main sector that helps the nation to gain finances. It is transportation. India has a huge landmass and the transport network in the country is excellent. The other factor that helps boost up the economy of India is communication.

Here are the Details that you Need to Learn in the Chapter:

Importance of Transport in India

Transport is important in India as both goods and people frequently move from one place to another. As the importance of finished products is high in the case of saving the economy of a country, the transport sector in the Indian landmass has high importance. 

Roadways in India: The roadways in India and their importance is high. At present, the total road network in the country is 2.3 million. Roadways are important for transporting such goods that cannot be taken by rail. Moreover, it helps people to move from one city or state to another comfortably. 

Railways: Railways in India is fully government property. India has an enriched railway network o0n which both frights and passengers move from one point of the country to another. It is surely one of the prominent economic lifelines of India.

Airways: Airways in India is another way the Indian administration can earn finances. This improves the economy of the country and the country can make an effort to enhance the economical equilibrium. 

Importance of Communication In India

Communication in a huge country like India can also be a prominent economic lifeline. You can learn about the best ways of communication like the post, media, telecom, and internet and their details in the chapter. Even the film industry of India falls under the communication lifeline in the country. 

Solved Examples 

Q1. Are Underdeveloped Economies Generally Cursed with Unemployment?

Answer: Yes, the underdeveloped economies generally are cursed with unemployment. The main reason being the lack of scopes for employment. Some examples of such countries are Afghanistan, Madagascar, etc. 

Q2.  Which is the Main Occupation of People in India?

Answer: Agriculture is the main occupation of the people in India. This is another lifeline of the country in terms of economy. However, a huge chunk of youth is shifting towards urban-based jobs right now.