Category: Geography Notes PPT

Clay is a fine-grained natural material of soil and contains many clay minerals. The size of the soil particles of clay is usually less than 0.005 mm. There are also rocks that are composed of clay particles. The rock here means a composition of soils, ceramic clays, clay shales, mudstones, glacial clays, and deep-sea clays. Characterised by the presence of clay minerals in varying amounts of organic and detrital materials, such as quartz, the clay geology is formed. The clay geology is also defined by plasticity which is developed when there is a molecular film surrounding the clay particles making it flexible and when in dried form it becomes hard and brittle and non-plastic. Most of the clay is formed as the result of weathering.

Features of Clay Geology

As mentioned above, the defining characteristic of clay is the plasticity when it is wet and the hard nature in dried form. Clay geology shows a huge variety and broad range of water content holding in between the minimum when it moist enough to be moulded and the maximum when the moulded clay is just dry enough for holding on to a shape. For example, the plasticity limit of kaolinite clay, from the kaolinite geology, ranges from about 36% to 40% and the liquid limit ranges between 58% and 72%.

The characteristics of the plasticity of clay geology are attributed to the mineral content such as hydrous aluminium phyllosilicate minerals. There are thin plates formed by interconnecting oxygen and hydroxyl ions which are part of the mineral content. These plates are tough and flexible thus providing the inherent characteristics of the clay. 

The chemistry of the clay minerals and their ability to retain nutritional content such as the cations like potassium and ammonium are important for soil fertility. Some clay minerals are known as the swelling clay minerals as they can take up water to great extent. They increase in volume with the absorption of water and when dried they shrink back to their original volume which can produce cracks and other distinctive textures such as “popcorn” texture in clay deposits. Examples include clay from the smectite geology site and bentonite geology site which is also known as the blue clay. Especially, the clay from the bentonite geology (or blue clay geology) isn’t favourable for civil engineering projects because of this property. 

Varieties of Clay geology

The main kinds of clays are obtained from the kaolinite geology, montmorillonite-smectite geology, illite geology and bentonite geology (or blue clay geology). There are a wide variety of clays, approximately, 30 different types of “pure” clays with a variety of mineral content. But the most naturally available clay deposits consist of the different types of clay along with other weathered minerals. The easiest way to identify clay minerals is X-ray diffraction rather than any other chemical or physical tests. Another kind of clay geology from which a type of clay is obtained is the fire clay geology. The fire clay geology, from which the fire clay is obtained, consists of mineral aggregates of hydrous silicates of aluminium with the presence or absence of free silica. 

Chlorite, vermiculite, talc and pyrophyllite are the types of minerals obtained from metamorphic rocks. The particles of such clay metamorphic rocks are very high in nutritional value and thus provide a significant amount of nutrition nurturing life. Thus, the plant life throws on the mineral content derived from the clay metamorphic rocks.

Concluding with the Importance of Clay

Clay is one of the most important of the various soil components. It has a wide variety of usage and essential material in various industries. As a component of the soil, they are responsible for providing the plants with the environment for growth and by extension nearly all life on the surface of the Earth. Their porous nature aids them in providing aeration, and in water retention. Clay is also a reservoir of nutrient material such as potassium oxide, calcium oxide, and nitrogen as well. 

Furthermore, they are used in pottery. This culture of pottery making surpasses many centuries of human history. Clay pottery also serves as a record of past civilizations. They are used as building materials in bricks either in baked form or even in raw form for ages. Fire clay is another type of clay that is used for the manufacture of ceramics such as fire brick which is used for making furnaces, fireplace, kilns, fireboxes, etc.

Along with bricks clay is also used for making tiles, the cruder types of pottery, as china clay or kaolin for the finer grades of ceramic materials. Another major usage of the china clay is paper coating and filler giving the paper a glossy appearance and increases the opacity of the paper. It is also used in refractory materials including fire brick, chemical ware, and melting pots for glass and also in heat insulators as it increases the resistance to heat. Wool scouring is another example of usage of a certain type of clay known as fuller’s earth. In the process of rubber compounding, the addition of clay increases the resistance for wear and eliminates the moulding troubles. 

Even in engineering, clay materials serve vital purposes. In the construction of the dams, clay provides water impermeability characteristic when added with porous soil. It serves the same purpose of controlling water loss in canals. Along with the limestone, clay either in pure or impure form is utilized as the raw material of portland cement. After treating it with acid, clay can be used as a water softener. Clay also helps in removing calcium and magnesium from the solution and substitutes sodium. One of the other major usages of clay is drilling mud i.e. heavy suspension consisting of chemical additives and weighting materials when employed in rotary drilling.

A continental shelf is the continent feature that is submerged under an area of relatively shallow water this is known as the shelf sea. The shelves are greatly exposed by the drops in the sea level during the glacial periods. The shelf which is being surrounded by an island is known as the insular shelf.

The margin which is located along the continent is situated between the continental shelf and the abyssal plain comprises a steep shaped continental slope which is surrounded by the continental rise, here the sediment from the continent which is above the cascades and down the slope has accumulated a pile of sediment which is at the base of the slope. This extends as far as 500 km (that is 310 mi) from the slope, this consists of the thick sediments which are deposited by the turbidity currents that are originated from the shelf and slope.  

Continental Zone 

Continental shelf or the zone is a broad type, relatively shallow submarine terrace which is made up of continental crust this is formed at the edge of a continental landmass. The geological feature of the continental shelves is very much similar to that of the exposed portion of the continent which is located adjacent to it. Most of the shelves have a gentle rolling topographic feature which is called a ridge. The Continental shelves consist of about 8 percent of the entire area which is covered by oceanic landforms.  

Structure of Continental Zone

A continental shelf extends from the coastal area to the depths of around 100–200 meters (that is approximately 330–660 feet). They are gently inclined towards the sea at an average slope of approximately 0.1°. In all such instances, the shelf ends towards the sea’s edge with an abrupt drop which is called the shelf break.  Below here lies the continental slope which has a steeper zone that merges with the oceanic floor and this is called the continental rise. Here the depth is roughly 4,000 to 5,000 meters (which is moreover 13,000 to 16,500 calculated in feet). 

Few continental margins like that of the Mediterranean coast of France and at the Porcupine Bank, off the western coast of Ireland, do not have a sharp definition of the slope but rather they maintain a generally convex shape structure towards the seafloor.

Widest Continental Shelf 

The widest continental shelf on the planet extends to about 1,210 km (in miles it is 750 miles) it is located off the coast of Siberia, Russia, and into the Arctic Ocean. The Continental shelves serve as an extension of the coastal plains. They are marked by the wide-sloping submerged plains which are approximately 7.4% of the world’s oceanic surface that sits above the continental shelves; they have a global average width of approximately 78 km (that is 48 miles).

The average width of the continental shelf is 65 km (that is 40 miles). Most of the continental shelves are very broad, gently sloping plains which are covered by relatively shallow type water. The water depth which is over the continental shelves is the average that are about 60 meters (which is 200 feet).

Continental Shelf Depth 

A Continental Shelf Depth is about 60 meters. The average width of the continental shelf is around 65 km (that is 40 miles). Most of the continental shelves are very broad and are the gently sloping plains that are covered by relatively shallow water. The water depth is up to 60 meters (200 feet).

200 meters deep is the Continental Shelf of Australia.
This shelf is very shallow, which is up to 200 meters deep, much compared to the thousands of meters deep in the ocean, it extends outward to the continental slope which is quite deeper where the ocean begins.

100m is the continental margin. This is in the Atlantic Ocean, where the continental margins have a shelf that is broad and flat. This reaches a depth of 100 m. Here the slope is the steep transitional area that is between the shelf and the rise, and this lies between the depths of 100 and 2,500 m.

Continental Platform 

In geological meaning, a continental platform is an area that is covered by relatively flat or by gently tilted sedimentary strata. This is an overlie basement that has consolidated igneous or metamorphic rocks which are formed by an earlier deformation. The Platforms, the shield, and the basement rock together make up the cratons. 

Continental Sea 

The Shelf seas or the continental sea refers to the ocean waters which are located on the continental shelf. Their wave motion is controlled by the summation influence of the tides, wind-forcing, and the brackish water which are formed from the river inflows. The regions are biologically highly productive, this is due to the mixing which is caused by the shallower waters and the enhanced current speeds. Despite all covering, only about 8% of the Earth’s ocean surface area, that is the shelf seas supports 15-20% of global primary productivity.

Continental Shelf Location

The Continental Shelf is located at the edge of a continent that lies under an ocean. Here the continents are the main divisions of the land on this Earth. The continental shelf which extends from the coastline of a continent to a drop-off point is called the shelf break. From this break, the shelf descends to the deep ocean floor which is called the continental slope. 

Continental Plain

Continental Plain or the continental margin landform is the broad and gentle pitch of the continental shelf that gives way to the steeper continental slope. Gradual the transition more is the abyssal plain. Here the region is sediment-filled and is called the continental rise. The continental shelf, slope, and rise are collectively known as the continental margin.

India is rich and prosperous in a lot of things, and for the same reason, India is one of the most popular countries today and will continue to be so in the future. A lot of things are unique and perfect in India, and one of them is the prosperous drainage system. India’s drainage system is very transparent and solid that informs a lot of things about the drainage process. Numerous small and big rivers flow from all directions and states in India, and some of them also combine at a particular place. This place may also be known as the rivers’ merging place, and such connecting sites improvise India’s drainage. 

Special Features about the Drainage System of India

There exists a lot of unique and crucial features about the drainage system of India, and some important ones among them can be listed as follows-

Unique Catchment Places Drainage System of India 

The peninsular rivers of India and the other river basins have a particular catchment area or section attached to its corner that prevents the overflow and mixing of the water’s toxic substances. This maintains a good pace with the drainage water and does not bother the whole river at all. 

These catchment areas also have some space for future infrastructure and development. The design does not remain outdated and incapable of handling future troubles that may be unavoidable at some points in time. 

Therefore, these catchments have facilitated giving a solid pace to the people in the first place for sure. 

The Perfection of the Peninsular Drainage System 

India has a vibrant river heritage and offers excellent, and the peninsular drainage system is the world-famous one among the other methods. India’s peninsular drainage system has a lot of various aspects and is distributed evenly throughout the coast and middle of Indian states. 

The peninsular rivers of India map show all the locations and peninsular spots in the country and describe the importance of the same. The primary and most essential rivers included in the peninsular drainage system are the Mahanadi, the Krishna, the Godavari, and the Kaveri. All these rivers are the base of the whole peninsular system, and for the development of the same, the infrastructure is also required to be impactful and creative in their ways. 

Vast Drainage Basins of India

Another fantastic speciality of India’s drainage system is the vast drainage basins present in it and the properties and advantages that they offer to the people in the first place. These basins also have prominent infrastructural and exponential places and are innovative and creative in their ways and manners. 

Therefore, having a vast and elaborated drainage basin is also the most important and prosperous aspect of India’s drainage system, and it is the responsibility of every individual to create an impressive and out-of-the-box infrastructural layout for the new generations to come and take advantage of the same. 

Some of the states in India always face the flood every year, which causes a lot of damage to people and properties. A proper drainage system will help in wiping out that danger. To conclude, India’s drainage system has evolved to a great extent in previous years. For the same reason, many new and innovative plans and policies have come into existence. The different types of drainage systems in India have connected many states in it with each other and have maintained good relations between them in the first place. 

For the betterment of a country’s good infrastructure, learning how the water divide in India is crucial and essential, and people should take this into proper consideration. Building an appropriate drainage system is the strength of every country, and cherishing it is the respective government’s sole responsibility.

Feldspar is a common raw material that is used in the process of glassmaking, ceramics, and to an extent as a filler and as an extender in the paint, plastics, and rubber industries. In glassmaking, alumina from feldspar actually improves the product’s hardness, durability, and resistance against chemical corrosion. In ceramics, the alkalis in feldspar are calcium oxide, potassium oxide, and sodium oxide. All of these act as a flux that eventually lowers the melting temperature of the mixture. In the process of firing, fluxes melt at an early stage. After which it forms a glassy matrix that bonds the other components of the system together. In the United States, roughly around 66% of feldspar are being consumed while in glassmaking, this includes glass containers and glass fiber as well. Ceramics (which are included in electrical insulators, sanitary ware, pottery, tableware, and tile) and other uses, like fillers.

Mnemonic

A mnemonic device, also known as a memory device, is literally any learning technique that aids information retrieval in human memory.

Suppose facing a geography memorization task, a way to make the learning simple is by employing a mnemonic device. Mnemonics are the memory aids which are in the form of easily recalled rhymes, phrases, or even acronyms that serve as a reference for the place names (or other information) that one is trying to study.

One example – the common mnemonic device that helps people memorize the names of the Great Lakes. Suppose the word “HOMES,” the five lake names will fall into place and in mind, that is Huron, Ontario, Michigan, Erie, Superior.

Sunstone

Sunstone is a kind of plagioclase feldspar that is when viewed from certain directions exhibits an appearance of spangled beads. Sunstone is found in Sweden, Southern Norway, and other state localities. They are also found on some beaches and along the mid-coast of South Australia. 

For the reflections from the inclusions of red copper, we have an optical effect. They are in the form of minute scales, that are hexagonal, rhombic, or found in irregular shapes. They are disposed parallel to the cleavage-plan principle.  The inclusions give an effect to the stone of an appearance similar to aventurine. For this feature sunstone is also known as “aventurine-feldspar”. The optical effect is called schiller and Oregon being the color of the Sunstone is due to the presence of copper. The mid-section of this crystal sparkles, and usually this color is darkest in the middle and fades toward the outer edges.

Oligoclase

Oligoclase is a mineral that is formed by a rock that belongs to the plagioclase feldspar.

Oligoclase is characterized by a high sodium feldspar crystallizing quality in the triclinic system. It is 6 to 6.5 as per the Mohs hardness and it has a specific gravity of 2.64 to 2.66. While, its refractive indices being nα=1.533–1.543, nβ=1.537–1.548, and nγ=1.542–1.552. In color texture, this is usually white in shade, with other shades of grey, red and green.

Oligoclase also occurs, often accompanying the orthoclase, which is a constituent of the plutonic igneous rocks like granite, syenite and diorite. This occurs in porphyry and in diabetic dikes and in sills as well. They are found in the volcanic rock andesite and in trachyte, where the presence is a defining feature. They also occur in gneiss. The developed and the most-largest crystals are the ones found with orthoclase, epidote, quartz, and calcite. The distinct texture of rapakivi granite is because of the oligoclase phenocrysts. Oligoclase is even found in the metamorphic rocks that are formed under transitional greenschist to amphibolite facies type conditions.  

 

Granulite Facies

Granulite facies are one of the major divisions of the mineral facies which are the types of metamorphic rocks, the rocks that are formed under the most intense temperature-pressure conditions are usually found in the regional metamorphism at the upper limit. At the uppermost limit of the facies, migmatite formation can occur. The temperature is 650–1,100 °C (1,200–2,000 °F) and a pressure of 3 to 10 kilobars (where 1 kilobar equals about 15,000 pounds per square inch) may be reached on. Under conditions of less intensified metamorphism, the rocks of the amphibolite facies occur. 

Garnet is the name used for a huge group of rock-producing minerals. These minerals share a familiar crystal composition and a generalized chemical structure of X₃Y₂ (SiO₄)₃. In that chemical composition, “X” can be Ca, Mg, Fe₂⁺ or Mn₂⁺, and “Y” can be Al, Fe₃⁺, Mn₃⁺, V₃⁺ or Cr₃⁺. Although garnet is often linked with the colour red. The red garnet gemstones can be encountered in almost any colour present and are well- recognized choices for jewellery of all types. That’s wonderful news if you’re in the market for this January garnet birthstone.

              

    

Occurrence of Garnet

These minerals are extensively found across the world in igneous, metamorphic, and sedimentary rocks. Most garnet stones are found near Earth’s surface when a sedimentary rock with greater aluminium content, such as shale, is put through heat and pressure intense enough to form schist or gneiss. Garnet is also found in the rocks of contact metamorphism, lava flows, deep-source volcanic outbreaks, subsurface magma chambers, and the soils and sediments formed when garnet-carrying rocks are eroded.

Chemical Properties of Garnet Stone

The commonly encountered minerals in the garnet group are inclusive of almandine, andradite, grossular, pyrope, spessartine, and uvarovite. They all possess a vitreous luster, a brittle tenacity, a transparent-to-translucent diaphaneity, and a shortage of cleavage. They can be found as solitary crystals, stream-tattered pebbles, granular aggregates, and gigantic occurrences. Their chemical structure, hardness, colours and specific gravity are listed below.

Garnet Mineral

Physical Properties of Garnet

Uses of Garnet Mineral

Following are the uses of garnet stone:-

• abrasive blasting granules

• abrasive grits and powders

• Filtration granules

• Waterjet cutting granules

• Gemstones (such as garnet birthstone, garnet earrings).

Garnets Gemstones

Garnet as gemstones has been in use for over 5000 years. It has been encountered in the jewellery of different Egyptian burials and was the most prominent gemstone of Ancient Rome. It is an alluring gem which is generally sold without treatment or enhancement of any kind. It is also durable and common that it can be used in jewellery as garnet earrings, garnet rings etc at a relatively low cost.

Even until now, garnet continues to be a popular gemstone of contemporary times. It caters to as a birthstone for the month of January and is a long-established gem given on a second anniversary.

 

Garnet Varieties

1. Almandine

A frequently found gemstone in the garnet family, almandines come in a huge array of colours. The mix of almandine-pyrope is the dark red variety customarily linked with garnets.

2. Andradite

One of the rarest garnets, these have the highest dispersion of all garnets, even greater fire than diamond. Demantoids, a variant of andradite, are particularly treasured.

3. Grossular

In contrast to other garnets in the family, grossulars are rarely red or even dark. However, they do form in every colour, even colourless, only other than blue. Their vibrant colours make them remarkable jewellery stones. Tsavorites contain an emerald-like green colour and can be a directive of high prices.

4. Hydrogrossular

Never transparent, these are often blueish green in colour. However, Hydrogrossular garnets are sometimes also found in white, pink, and grey.

5. Pyrope

Chrome pyropes display a red that can rival rubies. However,  pyrope garnet stones have a very dark tone.

Fun Facts

• The garnet family is one of the most in the gemological world.

• Although garnet is frequently linked with the colour red, these gemstones can be found in almost any colour and are preferred choices for jewellery of all types.

• Garnet is believed to be a red gemstone; however, it occurs in a variety of colours.

• Gem-quality garnets precipitate in every colour – with red being the most common and blue garnets being particularly rare.

Halite, also known as common rock salt, is a naturally occurring sodium chloride (NaCl) compound. Halite can be found in beds ranging in thickness from a few metres to over 300 metres (1,000 feet) thick on all continents. Evaporite deposits, so named because they are formed by the evaporation of salt water in partially enclosed basins, are typically found with limestone, dolomite, and shale beds. Halite can also be used as a sublimation product in volcanic areas, as an efflorescence in arid areas, and as an evaporation product near salt springs. As in salt domes and diapirs, deformation of halite beds may result in the extrusion of salt plugs through the overlying sediment. To put it another way, Halite is the mineral term for the substance we all know as “salt.” Its chemical name is sodium chloride, and “rock salt” refers to a rock that is mainly composed of halite.

How Does Halite Mineral Form?

Halite is primarily a sedimentary mineral that occurs in arid environments where ocean water evaporates. However, several freshwater lakes, such as North America’s Great Salt Lake and the Dead Sea between Jordan and Israel, are currently forming halite. Several massive salt deposits have accumulated over geologic time as a result of regular episodes of seawater evaporation in constrained basins. These deposits can be tens of thousands of feet deep. Salt domes can develop when they are buried deeply.

Halite can also be found in non-arid areas, in the form of underground deposits that can reach great depths. Drilling wells into the salt layer and taking in hot water to easily dissolve the salt into a brine is a popular method of mining underground Halite deposits. The brine is drained out after it has been coated with dissolved salt. The brine evaporates, leaving behind crystallised salt that can be harvested. The majority of commercially available Rock Salt is regrown from evaporated salt brine, not natural crystals. Evaporation at salt springs, where salty water falls out of the ground in a salt deposit and precipitates as rounded globular masses, also produces halite.

Salt is pushed upwards by an underground force through the soft ground in some underground salt deposits, forming arched structures known as salt domes. These deposits, which are very special geological formations, are also significant sources of salt mining operations.

Physical Properties of Halite Rock

1. Halide is a chemical classification.

2. Color, When pure, colorless or white; impurities contain a variety of colours, including yellow, green, black, brown, and red.

3. Vitreous lustre.

4. Transparent to transparent diaphaneity. 

5. Cleavage is Perfect, cubic, three right-angle directions

6. Diagnostic Characteristics: Cleavage, solubility, and salty taste (Taste testing is not recommended.) Some minerals are poisonous or tainted as a result of other people’s consumption.)

7. Chemical Composition is NaCl.

8. The Crystal System is Isometric.

9. Winter road treatment, a source of sodium and chlorine for chemical processes, food processing, and seasoning are only a few of the applications. In the section below, we’ll go through each use in detail. 

Uses of Halite Rock

Salt is widely used in cooking as a taste enhancer and in the curing of a number of foods, including bacon and fish. Various cultures use it in food storage processes. Larger bits may be ground in a salt mill or dusted over food as finishing salt with a shaker.

Halite is also commonly used to manage ice in both residential and public conditions. Since brine (a mixture of water and salt) has a lower freezing point than pure water, placing salt or saltwater on ice that is below 0 degrees Celsius (32 degrees Fahrenheit) can cause it to melt — this is known as the freezing point depression. After a snowstorm, it’s normal for homeowners in colder climates to spread salt on their sidewalks and driveways to melt the ice. It is not necessary to use so much salt that the ice melts completely; instead, a small amount of salt can soften the ice, allowing it to be easily extracted using other methods. Several cities will spray a mixture of sand and salt on roads before and after a snowstorm to improve traction. Salt brine is more effective than dry salt because moisture is needed for the freezing-point depression to work, and wet salt sticks to the roads better. Otherwise, the salt would be washed away by traffic.

Rock salt is occasionally used in cultivation in addition to de-icing. Inducing salt stress to suppress the growth of annual meadow grass in turf development is an example of this. Other methods include submerging weeds in salt water to dehydrate and destroy them, preventing them from harming other plants. Salt is also used as a cleaning agent in the home. Its coarse design enables it to be used in a variety of cleaning situations, including grease/oil removal, stain removal, and drying and hardening sticky spills for easier cleanup.

For different dishes, some cultures, especially in Africa and Brazil, prefer a wide variety of different rock salts. Pure salt should be avoided because different shades of salt signify the presence of various impurities. Many recipes call for specific types of rock salt, and imported pure salt is often tainted to suit local tastes. Salt was once used as a source of currency in barter systems, and it was solely under the control of authorities and their appointees. The practice of salting the earth was used by some ancient civilizations to make captured enemy land infertile and inhospitable as a form of dominance.

Distribution of Halite Rock

• Hallstatt, Salzburg, and Hall, near Innsbruck, Tirol, Austria. From the Swiss town of Bex in the canton of Vaud.

• In Saxony-Anhalt, Germany, from Stassfurt-Leopold Hall, 34 kilometres south of Magdeburg.

• Big crystal deposits at Wieliczka (Galicia) and Bochnia, Poland. Sicily, Italy, Girgenti and Racalmuto

• In Punjab, India, on the Salt Range.

• In the United States, large crystals at the Potash Corporation of America mine, Carlsbad potash district, Eddy County, New Mexico; various salt domes along the Gulf Coast; and the Permian Basin of Texas and New Mexico; large crystals at the Potash Corporation of America mine, Carlsbad potash district, Eddy County, New Mexico.

Pink Halite

Pink Halite is a type of Halite that has had bacteria from various algae species taint its colour. Halite is a common mineral found near oceans and salt lakes and is regarded as the “natural type of salt.” The masses and tubular crystal structure of this stone can be found.

Conclusion

Halite can be found in beds ranging in thickness from a few metres to over 300 metres (1,000 feet) thick. Halite is primarily a sedimentary mineral that occurs in arid environments where ocean water evaporates. Several freshwater lakes, such as North America’s Great Salt Lake and the Dead Sea between Jordan and Israel, are currently forming halite. Drilling wells into the salt layer and taking in hot water easily dissolves the salt into a brine. The brine is drained out after it has been coated with dissolved salt. The majority of commercially available Rock Salt is regrown from evaporated salt brine, not natural crystals. Evaporation at salt springs, where salty water falls out of the ground in a salt deposit and precipitates as rounded globular masses, also produces Halite. Halite is also commonly used to manage ice in both residential and public conditions. Salt brine is more effective than dry salt because moisture is needed for the freezing-point depression to work. Rock salt is occasionally used in cultivation in addition to de-icing. Pure salt should be avoided because different shades of salt signify the presence of various impurities. The practice of salting the earth was used by some ancient civilizations to make captured enemy land infertile and inhospitable as a form of dominance.  Many recipes call for specific types of rock salt, and imported pure salt is often tainted to suit local tastes. For different dishes, some cultures, especially in Africa and Brazil, prefer a wide variety of different rock salts.