Category: Geography Notes PPT

Opal is naturally found in a white coloured semi-precious gemstone composed of a silicate mineral family recognized for its marvellous ‘play of colours’. This astrological alternative of precious diamond is worn for gaining success in innovative pursuits, lavish lifestyle, social/financial prominence, matrimonial harmony and good health. Over thousands of years, people have quarried and treasured opals. These striking opal stones have energized a rich body of folklore. (Thus, opal gemstones have been considered both the luckiest and unluckiest stones one can wear).

          

Factual Information About Opal Gemstone

Assembled Opal Gems

A triplet from assembled opal gems adds a transparent quartz cap and makes for a  good opal stone ring and opal earrings, since the hard quartz keeps the softer opal from scratching.

How to Determine Synthetic Opals?

Synthetic or lab-created opals are actually the real opals, but they’re grown in laboratories rather than yellowish-brown underground. They encounter the same formation processes, only at a stimulated rate in controlled settings.

Synthetic opals may exhibit an intense display of colour, generally in a mosaic pattern. With high magnification and backlighting, you can find a scale-like, snake skin or chicken wire structure in the pattern. When put under high magnification with transmitted light, synthetics may display a dendritic structure. Synthetic opals don’t phosphoresce (sparkle or twinkle) and may also stick to the tongue.

How to Detect Fake or Imitation Opal Gems?

Contrary to lab-created opals, imitations only simulate the physical look of opals. These imitations are essentially made from glass or plastic.

Plastic imitations or stimulants are soft and can be dissected with a sharp needle. They do not sparkle or twinkle (phosphoresce).

Glass stimulants essentially consist of glass bubbles and swirl marks. They also do not phosphoresce. Their refractive index (RI) and specific gravity (SG) are also generally higher than natural opal.

Care For Opal Stones

Nowadays, used frequently as opal necklace, opal rings and other opal jewellery, extra care of the delicate gemstone is well worth it. Highly sensitive to changes in temperature as well as a “crazing”, that implies they can easily form cracks or “craze” as they dehydrate, and must be kept cautiously.

Opals kept in water must be dried properly and cautiously before cutting.

Sometimes opals in rings can become chalky white and weary. This may owe to a network of scratches on the opal surface that dismantle the polish and dulls the colour play. However, a simple re-polishing can generally correct this. Having a hardness of only 5.5 makes them quite susceptible to scratching. Opals are thus usually not recommended for ring stones, unless the stone is positioned in a protective setting or a triplet for occasional wear.

Opal Stone Facts and Information

• Opal stone is sedimentary.

• Many ancient references to opal may actually indicate other gems, such as the iridescent iris agate.

• Under proper conditions, water seeps through the earth, becoming affluent in dissolved silicates. When water makes way through a cavity, it accumulates the silicates as microscopic spheres, forming opals.

Phyllite is a foliated metamorphic rock that is primarily composed of quartz, mica, chlorite, and sericite. The Phyllite rock is formed by the slate that is further metamorphosed so that the coarse-grained mica attain a preferred accommodation. The word Phyllite is derived from the Greek phyllon meaning “ leaf”. 

Phyllite metamorphic rock has an excellent tendency to split into the sheets and is generally black to grey or light greenish-grey. The appearance of the rock is commonly crinkled or wavy.  The Phyllite rock is commonly found in Dalradian metasediments of northwest Arran. The Tretorn phyllites rock and Woolgarden phyllites rock are found in North Cornwall.

Phyllite Properties

The Table Given Below Shows the Phyllite Mineral Composition

Phyllite Mineral Composition

Phyllite Composition

According to the Phyllite Composition Table Given Above, We Can Say:

• Phyllite has a coarse grain of mica such as Sericite and Muscovite.

• Phyllite includes almost half the amount of quartz mineral in its composition.

• Quartz and feldspar are found in large quantities in phyllite.

• Crystals of ratile, cordierite, andalusite, staurolite, and garnet are also found in phyllite.

• Large crystals or porphyroblast are found in the horizontal axis in phyllite.

• Organic minerals are metamorphosed into graphite and give phyllite black to dark colour shades and submetallic luster.

Phyllite Uses

Phyllite is a soft and durable metamorphic rock. It is often used as a floor tile, decorative aggregates, and decorative stone in counterparts. It is also used as an exterior building, or facing stone, and garden decoration. The other phyllite uses include commemorative tablets, cemetery markers, writing tablets, etc.  The slabs of Phyllite are often trimmed and used as a landscape, paving, or sidewalk stone. 

Phyllite Parent Rock

The phyllite parent rocks are shale, pelite, or slate which further comes from a shale protolith. Shale can be transformed into schist, slate or genesis depending on the degree of heat and temperature. 

Similar to slate, phyllite has a typical texture known as phyllitic sheen and has the feasibility or tendency to split into sheets like slate rocks.

Phyllite Rock Formation

The phyllite rock forms when Slate rock further transformation occurs, and very coarse grain mica attains perfect orientation.

• The slate rock consists of clay minerals in a semi-random orientation.

• When the slate rocks are buried further and attain a high temperature, the extremely fine clay transforms into mica and the flacks of clay minerals gain a horizontal positioning.

• The chemical reactions and heat transform clay mineral grain into chlorine or mica minerals. They are enlarged forms of coarse-grain clay flakes.

• Hence, they form phyllite rock. 

• Further metamorphosis and sedimentation process transform Phyllite into Schist, and then Geiss by enlarging mica flakes.

Where is Phyllite Rock Found?

Phyllite rock is found throughout the world  in many regions such as:

Did You Know?

• Large crystals or porphyroblasts are found in phyllite rock in parallel orientation.

• Organic minerals metamorphosed into graphite and give phyllite a black to dark grey shades that give it a submetallic luster.

• Phyllites are most commonly found in the Dalradian metasediments of northwest Arran.

• Quartz and feldspar are found in large quantities in phyllite.

• Phyllite has a good tendency to split into sheets.

• Fine grains of mica minerals such as Muscovite and sericite are also found in phyllite

• Tredorn Phyllite and Woolgarden phyllites are found in North Cornwall.

Pumice is a volcanic rock, which in powdered or dust form is called ‘pumice.  This rock has a feature of a highly vesicular rough-textured volcanic glass, which might contain crystals. The rock has a typical light-colored context. There is another volcanic rock known as Scoria which is different from this Pumice rock, the Scoria rock has larger vessels, thicker vesicle walls, and also it is darker in color and denser inconsistency.

Pumice is created when the rock is super-heated. The rock is formed in highly pressurized conditions, being violently ejected from the volcano. While due to simultaneous rapid cooling and rapid depressurization the rock gets its unusual foamy configuration.  

Pumice Rock

Pumice is a very light and porous volcanic rock that forms during the explosive eruptions of the volcano. During the volcanic eruption, the volcanic gases dissolve in the liquid portion of viscous magma, and then it expands very rapidly to create a foam or a froth. The liquid part of the rock is called the froth which quickly solidifies to glass around the gas bubbles. The volume of the gas bubbles present in this rock is generally so large that the rock is lighter than water and thus it floats in water. 

Pumice is a textural term for a type of volcanic rock which is a solidified frothy lava that is composed of highly microvesicular glass pyroclastic with very thin, this is translucent bubble walls of extrusive igneous rock. This is commonly, but not exclusively of a silicic or felsic to an intermediate in composition (e.g., rhyolitic, dacitic, andesite, Pantelleria, phonolite, trachyte), but the occurrences of this basaltic and other compositions are also known. The pumice is pale in color while ranging from white color or cream color or greyish in shade, also they can be green-brown or black. The rocks form when the gases exsolving from the viscous magma which nucleate the bubbles and cannot readily decouple from the viscous magma after chilling into the glass. Pumice is also a common product of explosive eruptions (Plinian and ignimbrite-forming) this commonly forms zones in the upper parts of silicic lavas. The Pumice has an average porosity of about 90%, and initially, the rock floats on water.

Pumice Uses 

• Pumice is an important rock for the industrial mine industries which is used to produce superior-quality cement and a lightweight, isolating for the building materials.

• Pumice is a very light weighted porous and abrasive material that has been used for quite a few centuries in the construction and the beauty industry as well as in early medicine. 

• This is also used as an abrasive, in polishes, or the pencil erasers, and the production of stone-washed jeans.

• This is abrasive in conditioning the “stonewashed” denim.

• This rock is an abrasive in the bar and liquid soaps such as the “Lava Soap”

• Works as an abrasive in pencil erasers.

• The rock is abrasive in skin exfoliating products.

• It works fine in the abrasive used for polishing.

• Also used in a traction material on snow-covered roads.

• A traction enhancer in the tire rubber.

Pumice Stone Meaning 

A pumice stone is a piece of pumice that is used in rubbing over the skin to clean the skin or make it even or smoother. Also, the term ‘pumice’ is an uncountable noun.

Pumice is a type of grey stone that is formed from a volcanic eruption and this is very lighter in weight which can be rubbed over the surfaces mainly the skin which is required to make it smoother.  

Is Pumice a Igneous Rock?

Pumice is a kind of igneous rock with a foamy texture. The name is derived from the Latin word which is “Pemex” this means “foam” and being evident of history this has been given many other names for its formation was unclear. In earlier times it was called “Spuma Maris”, which means froth of the sea in Latin word, as it was a frothy material that was thought to be a hardened sea foam. 

The hydrosphere is the total amount of water present on Earth. The water from water bodies such as lakes, seas and rivers, oceans, the water present under the ground and the water from the air, everything is included in the hydrosphere river and ocean waters. This water can be of any form – solid (in the form of ice), liquid or gas (vapours). The solid water is present in the form of ice sheets, glaciers and icebergs. Liquid water is present in the water bodies such as lakes, river and ocean waters. There is also groundwater which is in liquid form. The gaseous form of water can be found in the form of clouds and fogs.

River and Ocean Waters

Rivers are naturally flowing water bodies, generally freshwater bodies that flow towards another river lake and ocean. The rivers have a starting point from where it starts flowing. This starting point is known as the headwater. This starting point or headwater can be from a snow melting point or rainfall or a bubble up from groundwater or a lake or a pond. The other end of the river is called its mouth. The river empties into a river stream sea ocean through this mouth. 

Composition of Ocean Waters

The seawater is more uniform in composition with respect to the river water. Seawater has 3.5% of dissolved salts in it whereas river water has only 0.012% of dissolved salts. If we calculate the average density, the world’s ocean is approximately 2.75% denser than river water. 

Of the average of 35 parts per 1000 salts of the seawater, 30 parts are sodium and chlorine and 4 parts are magnesium and sulphate. The remaining 1 part of the saline water is constituted with 0.4 part of calcium and potassium each and 0.15 part of the carbon in the form of carbonate and bicarbonate. Along with these elements, the other nutrients found in the ocean or seawater are phosphorus, nitrogen and silicon.

Composition of River Waters

The water flowing in the rivers is freshwater. It contains less than 1% salt. In this 1% salt, 58 parts are carbon in the form of bicarbonate, 39 parts are calcium, sulfur in the form of Sulphate and silicone as dissolved monomeric silicic acid. The remaining 3 parts are chlorine, sodium and magnesium. 

Stream and Lake Waters

Lake waters contribute a small percentage of water in the hydrosphere but it is an important source of freshwater. The lake and stream waters are used for household purposes, agricultural purposes and also for industrial purposes. The composition of stream and lake water varies from place to place and season to season. The main source of the dissolved minerals of the stream and lake waters are the rocks through which this water flows. When slightly acidic water hits the rocks, the minerals start dissolving in them. Another factor affecting the composition of stream and lake water is biomass. The biomass helps in neutralizing the pH of the precipitation. Any biological activity in the stream or lake like photosynthesis can change the pH and dissolved oxygen content. Temperature also influences the number of dissolved gases in the water.

The composition of lake water is influenced by evaporation. When the water evaporates, the dissolved minerals are left behind. The more the evaporation will be, the more will be the concentration of dissolved minerals. And if the evaporation continues, minerals such as calcite (CaCO3) and gypsum (CaSO4.2H2O) can precipitate from the solution. 

Ground Water

The factors that influence the surface water such as river lake and ocean, sea, pond water also influence the groundwater. The groundwater is always in contact with the rocks. But they move slowly as compared to the surface waters. The surface water may move at a speed of a few kilometres per hour while the groundwater moves a few centimetres in a day.  As a result of this slow movement, the groundwater contains more minerals than the surface water. 

The composition of groundwater is influenced by the geological materials through which the water passes, the types of reactions taking place and the contact time. The contact time may be a few days to 10,000 years. 

Generally, the groundwater has a total dissolved solids content of less than 250 mg/L. But in some areas, groundwater with a total dissolved solid content of greater than 100000 mg/L has been found. This saline groundwater is found in marine sedimentary rocks and also in ancient metamorphic and igneous rocks. Saline groundwater is formed by the three ways – 

In this article, you will learn about the meaning of seawater, origin, composition, and impacts, etc. Seawater, or saltwater, is sea or ocean water. On average, seawater in the oceans of the world has a salinity of about 3.5 percent. This means that every kg of seawater contains approximately 35 grams of dissolved salt. The average surface density is 1,025 kg/l. Seawater is denser than fresh water and pure water because dissolved salts raise the mass by a larger proportion than the volume. The seawater freezing point lowers down as the concentration of salt increases.

Seawater is a rich source of numerous commercially important chemical elements. Most of the world’s magnesium is obtained from seawater, but so are large amounts of bromine. In some parts of the world, sodium chloride (table salt) is still produced by the evaporation of seawater. In addition, when desalinated, water from the sea can provide an unlimited supply of drinking water. Several large desalination plants are designed in dry areas along the coastlines of the Middle East and elsewhere to ease freshwater shortages. 

Seawater Meaning

Seawater Meaning: Seawater is a mixture of 96.5 percent water, 2.5 percent salts, and smaller amounts of other substances, including inorganic and organic dissolved solids, particulate matter, and few other atmospheric gases.

Origin

Scientific findings on the roots of sea salt began with Sir Edmond Halley in 1715, who proposed that the salt and other minerals would be transported to the sea by rivers after the rain had washed it out of the ground. Upon reaching the ocean, these salts were concentrated as more salt arrived over time. Halley concluded that most of the lakes that do not have ocean outlets have a high salt content. Halley referred to this process as “continental weathering” Halley’s theory was partially correct. In addition, when the ocean formed, sodium leached out of the ocean floor. The presence of other dominant ions of salt, chloride, tends to result from the outgassing of chloride with other gasses from the Earth’s interior mostly through volcanoes and hydrothermal vents. Consequently, sodium and chloride ions were the most abundant components of sea salt. Ocean salinity has been steady for billions of years, most possibly as a result of a chemical/tectonic system that removes as much salt as it deposits; for example, sodium and chloride sinks include evaporite deposits, pore-water burials, and marine basalt reactions.

Composition

Seawater comprises more dissolved ions than any kind of freshwater. Nevertheless, the ratios of the solutes vary dramatically. For example, although seawater comprises about 2.8 times more bicarbonate than river water, the percentage of bicarbonate in seawater as a ratio of all dissolved ions is much lower than in river water. Bicarbonate ions account for 48 percent of river water solutions, but only 0.14 percent for seawater. Differences such as these are mainly owing to the varying residence times of seawater solutes; sodium and chloride have quite long residence periods, while calcium tends to precipitate much faster. Sodium, chloride, magnesium, sulfate, and calcium are the most abundant dissolved ions in seawater.

Due to their common chemical and physical properties, several of the features of seawater correspond to those of water in general. For instance, the molecular structure of seawater, like that of freshwater, favours the creation of bonds between molecules. Some of the distinct features of seawater are directly related to its salt content. For instance, the viscosity of seawater is higher than that of freshwater due to its higher salinity. Seawater density is also higher for the same reason. The freezing point of seawater is lower than that of pure water, and its boiling point is higher.

Human Impacts

Changing climate, increasing atmospheric carbon dioxide, heavy metals, and pollution in many ways are distorting global ocean geochemistry. The rate of change for some aspects is significantly higher than in the historical and recent geological record. Primary issues include increased acidity, reduced subsurface oxygen in waters, increased level of coastal nitrogen, and widespread increase in mercury and persistent organic pollutants. Most of these abnormalities are either directly or indirectly linked to human burning of fossil fuels, fertilizer, and industrial activity.

Even though oceans are an enormous reservoir, human activities have begun to affect their chemistry on a local and global scale. The accumulation of nutrients to coastal waters results in increased phytoplankton growth, high concentrations of dissolved and particulate organic materials, reduced penetration of light through seawater, and variations of the community structure of sub-dwelling organisms. Through industrial and automotive emissions, the concentration of lead on the surface of the ocean has increased dramatically on a global scale compared to pre-industrial levels.

Did You Know?

• Saltwater functions as a conveyor belt to transport heat around the planet. 

• Even though humans cannot remain healthy drinking saltwater, many creatures in the oceans and seas depend on saltwater for their very existence. 

• Fish living in saltwater will end up dying in freshwater, and vice versa.

In Geological time, the Silurian period is the third period of the Paleozoic era. It started 443.8 million years ago and ended 419.2 million years ago, extending from the ending of the Ordovician period to the beginning of the Devonian period. During this period, continents’ highlands were much lower and sea level was rising. Sea level rose drastically as the huge glacier from the Late Ordovician ice age melted.  

The immediate changes in climatic conditions permitted many faunal groups to recover from the extinction of Late Ordovician times. Large expanses of different continents became flooded with shallow seas, and mound-type coral reefs were common. Fishes were extensive. Vascular plants began to take over coastal lowlands during this period whereas the continental interiors became infertile. 

When Did the Silurian Period Start?

The Silurian period was the period from the end of the Ordovician period, at about 443.3 million years ago, to the beginning of the Devonian period, 419.2 million years ago. The Silurian period is considered to be the shortest period of the Paleozoic Era.

Silurian Period Significant Events

Life on Land

It was during this period that the first life came about from water and colonized the land. Increased ozone from photosynthetic water plants provided protection from the ultraviolet rays, making the terrestrial environment friendly to those organisms that could prevent desiccation.

First Vascular Plants

The first plant with an internal vascular channel was seen in Silurian period. Plants were not able to transfer food and gases to other parts of the structure, allowing a considerable amount of increase in size.

First Insect

The first insect seen in the Silurian period, was probably the first animal to come out of water.

First Jawed Vertebrates

The first fish with jaws appeared during the Silurian period, providing much better predictability and eventually giving rise to vertebrates known today. 

Silurian Period Climate

The climate was much warmer during the Silurian period. This caused the melting of glaciers and sea levels to rise.  Even though the sea level was rising, there was a place where the land was rising as well. This was due to the mountain building as the continental plates collided. In these places, the seas moved away from the coasts or evaporated from the shallow zones. Plants that had to live in coastal water had to live on land or die.

Fishes Gained Importance During the Silurian Period

Fishes gained much importance during the Silurian period. Most of the fishes were jawless at the beginning of the Silurian period. There were some earlier vertebrates, animals with soft cartilage bones. By the end of the Silurian period, animals with jaws and real bones were swimming in water. These animals soon would rule the seas.

Terrestrial

The most significant progressive development of this period was that of the first true terrestrial ecosystem. 

The first fossil records of vascular plants, that is, land plants with tissue was of those which carries food, occurred during the Silurian period. The vascular plants were simple plants that had not developed individual stems and leaves.

By the middle of the Silurian period, a very simple early terrestrial community with simple plant producers, millipede herbivores, centipede and arachnid carnivores, worm detritivores, and fungal decomposers had developed.

The Mid-Late Silurian terrestrial biota included small plants along with the water’s edge and arthropods such as trigonotarbids and myriapods. Fungi, nematodes, and perhaps earthworms were most likely present as well, although they did not leave a fossil record (except for possible fungi).

Did You Know?

• The name Silurian originated from the Celtic from Whales.

• During this period, the sea fluctuated between transgression and regression due to the climatic change and continental buildup.

• The first fossil record of the Vascular plants appeared in the second half of the Silurian period.