Category: Geography Notes PPT

A mesa is a flat-top tableland with one or more steep sides commonly found in Colorado Plateau regions of the United States. Mesas consist of flat-lying soft sedimentary rocks covered by more resistant layers or layers of hard rock. For example, shales overlaminated by sandstones. The resistant layer functions as a caprock that forms the flat summit of the mesa. The caprock can consist of either sedimentary rock such as sandstone or limestone or a deeply eroded duricrust. 

A butte is also a flat-topped hill with steep sides, though smaller in area than a Mesa. However, there is no acceptable way to separate mesa from butte or the plateaus. For example, the flat-topped mountain known as mesa, in the Cockburn range of North-Western Australia has an area as much as 350 km (220 mi) in opposition to flat-topped hills which is as small as 0.1 kilometers (0.062 mi) in area, in the Elbsandsteingebirge, Germany.

Define Mesa

A mesa is an isolated, high plateau with a flat top and steep slides that has been separated by the broadening of canyons. Mesas are mostly found in the drier southwestern states of New Mexico, Colorado, Utah, and Arizona.

Mesa Formation

Mesas are generally formed when the horizontal stratification of rock is pushed upwards by tectonic force. Erosion and weathering then act on these rocks, and the weaker layer of rocks are eroded away, leaving behind more resistant rocks which become elevated above their surroundings in a process known as differential erosion. The more resistant rock types include conglomerate, sandstone, quartzite, basalt, limestone, lava flows, chert, and sills. Lava and sills, in general, are very resistant to weathering and erosion, and often form the flat top, or caprock of the mesa. The less resistant rock layers are generally made up of shale, a softer rock that weathers and erodes easily. 

The mesa formation is quite a lengthy process and can take millions of years. The variation in different types of rocks during the formation of mesa also affects the steepness and sides of mountains. More resistant rock layers form cliffs whereas less resistant rock types form gentle slopes. Eventually, the basal sapping causes the cliffs to be cut off from the mesa. 

Mesa on Mars

Mesas are not restricted to Planet Earth, as these geographical features have been found on an extraterrestrial location known as Mars.  A translation zone on Mars lies between highly cratered highlands and low cratered lowlands. The younger lowland manifests steep-walled mesas and knobs. The mesas and knobs are departed by flat-lying lowlands. They are considered to form from ice-facilitated mass wasting processes from the ground or atmospheric sources. The mesas and knobs diminish in size with escalating distance from the highland escarpment. The relief of the mesas ranges from nearly 2 km to 100 m depending on the distance they are from the escarpment. 

How Mesas are Related to Two Landforms: Butte and Plateaus?

Mesas are closely related to two landforms known as butte and plateaus. The basic difference between these landforms is size. The surface area of mesas ranges between 11.251 square feet and four square miles whereas plateaus are larger, i.e., more than 4 square miles, and buttes are smaller (11,250 square feet or less).

The simple difference between mesa and butte is that some say mesa has more width than its height whereas others say a butte has more height than its width.

The three landforms mesa, butte, and plateaus are also related to the sense that over time, one landform can transform into another. For example, a plateau can be eroded into various forms. Similarly, a mesa can be eroded multiple times until its height is greater than its width, at this point it is considered a butte. A butte will ultimately erode into a peak, which will ultimately crumble and fall to the surface.

Did You Know?

• The largest mesa in the world is Grand Mesa, found in Western Colorado in the United States.

• A mesa on Mars can be viewed easily from satellites.

• The term Mesa is used to describe flat-topped mountains in the Southwestern United States.

The mica family’s most common mineral is muscovite. It is a rock-forming mineral that can be found in igneous, metamorphic, and sedimentary rocks. It easily cleaves into thin transparent sheets, much like other micas. The surface of Muscovite sheets has a pearly to vitreous luster. They are translucent and nearly colorless when held up to the light, but most have a faint brown, yellow, green, or rose tint. Muscovite meaning is a silvery-grey mica that can be found in a variety of rocks.

Muscovite gets its name from Muscovy-glass, a name given to the mineral in Elizabethan England because it was used as a cheaper alternative to glass in windows in medieval Russia (Muscovy). In 1568, George Turberville, the secretary of England’s ambassador to the Muscovite tsar Ivan the Terrible, wrote letters to the Muscovite tsar Ivan the Terrible, which became widely known in England during the sixteenth century.

Muscovite Mineral

Muscovite, also known as common mica, potash mica, muscovite mica, or isinglass, is potassium and aluminum-rich silicate mineral. The most common mica is muscovite, which can be found in granites, pegmatites, gneisses, and schists, as well as as a contact metamorphic rock or a secondary mineral resulting from the alteration of topaz, feldspar, kyanite, and other minerals. It’s a feature of peraluminous rock, which has a relatively high aluminum content. It is often found in enormous sheets in pegmatites, which are commercially valuable. Muscovite is used to make fireproofing and insulating materials, as well as lubricants to some degree. The muscovite mica Chemical Formula is: KAl2(AlSi3O10)(OH)2

Muscovite Properties

Physical Properties

Muscovite can be distinguished by its perfect cleavage, which allows it to be broken into thin, flexible, elastic, colorless, translucent sheets with a pearly to vitreous luster. It is the only common mineral that possesses these characteristics.

Muscovite mica hardness of 2–2.25 perpendicular to the [001] face, 4 perpendicular to the [001], and a specific gravity of 2.76–3.25 perpendicular to the [001]. It can be clear or translucent and can be colorless or tinted with greys, browns, greens, yellows, or (rarely) violet or red. It has a high birefringence and is anisotropic. It has a monoclinic crystal system. It has a near-perfect basal cleavage, resulting in incredibly thin laminae (sheets) that are often very elastic. Muscovite sheets measuring 5 meters by 3 meters (16.5 feet by 10 feet) were discovered in Nellore, India.

Chemical Properties

Muscovite is a potassium-rich mica. 

Muscovite Chemical Formula :KAl2(AlSi3O10)(OH)2 

Other ions with a single positive charge, such as sodium, rubidium, or cesium, are also substituted for potassium in this formula. Magnesium, copper, lithium, chromium, or vanadium are also used instead of aluminum.

As chromium replaces aluminum in muscovite, the substance turns green and is referred to as “fuchsite.” Fuchsite is commonly found disseminated in greenschist facies metamorphic rocks. It is sometimes abundant enough to give the rock a distinctly green hue, and these rocks are referred to as “verdict.”

Muscovite Uses

• Paint: In color, ground mica is used as a pigment extender. It keeps pigment suspended, prevents chalking, shrinking, and shearing of the finished surface, and brightens the tone of colored pigments by reducing water penetration and weathering. Mica flakes are used in some automotive paints to provide a pearlescent luster.

• Joint Compound: Ground mica is primarily used in gypsum wallboard joint compound to conceal seams and blemishes. Mica acts as a filler, increases the compound’s workability, and prevents cracking in the final product. In 2011, joint compounds accounted for nearly 70% of all dry-ground mica consumed in the United States.

• Plastics: Ground mica is used in the car industry in the United States to increase the performance of plastic components. Ground mica particles are used as a sound and vibration absorber in plastics. Stability, stiffness, and strength are all mechanical properties that can be improved.

• Muscovite Mica Uses:  The majority of sheet mica is used in electronic devices. The sheets are cut, punched, stamped, and machined to precise dimensions in these applications. Diaphragms for oxygen-breathing equipment, navigation compasses marker dials, optical filters, pyrometers, retardation plates in helium-neon lasers, missile systems parts, medical electronics, optical instrumentation, radar systems, radiation detector windows, and calibrated capacitors are only a few of the applications.

• Cosmetics: In the cosmetics industry, some of the highest quality ground mica is used. Ground mica is used in blushes, eyeliner, eye shadow, foundation, hair and body glitter, lipstick, lip gloss, mascara, and nail polish because of its pearly luster.

• Drilling Mud: Ground mica is a drilling mud additive that aids in the sealing of porous parts of the drill hole, thereby reducing circulation loss. Drilling muds consumed about 17% of the dry-ground mica consumed in the United States in 2011.

During the Ordovician, Life expanded tremendously in diversification and multiplicity. There existed a wide range of reef complexes in the tropics. The early Ordovician had been considered to be quite warm, at least in the tropics.

Throughout the time of the Ordovician period, part of the Paleozoic era, a plentiful variety of marine life prospered in the vast seas and the first primitive plants started to occur on land—prior to the second-largest mass extinction of all time terminated the period.

Age of Invertebrates

The Phanerozoic is classified into 3 eras i.e.:

• the Paleozoic (550 to 250 million years ago),

• the Mesozoic (250 to 65 million years ago)

• Cenozoic (65 million years ago to the present)

The Paleozoic has been known to be the Age of Invertebrates due to the rapid development of invertebrate animals during that time.

Invertebrate

Invertebrate life became growingly complex and diverse through the Ordovician. Both calcareous and siliceous sponges are well recognized; among other types, the stromatoporoid first occurred in the Ordovician. Even the Tabulata (platform) and rugosa corals (horn corals) occurred first in the Ordovician, the solitary or horn corals being particularly distinguishing. Brachiopods (lamp shells) and Bryozoans (moss animals) have been a dominant component of many accumulations. Molluscs were also quite common and included the bivalves, chitons, cephalopods, scaphopods (tusk shells), rostroconchs (single-shelled molluscs), gastropods, and monoplacophorans (limpet-shaped, segmented molluscs).

Most of the planet’s landmasses combined to create the supercontinent of Gondwana, which included the continents of Africa, South America, Antarctica, and Australia. Gondwana floated along the south throughout the period, ultimately establishing on the South Pole. The landmass that progressed towards being North America was combined into the supercontinent of Laurentia, which was isolated from Gondwana by the narrow Iapetus Ocean. 

Mass Extinction of Ordovician

Despite the extreme expansion of life during the Ordovician Period, there has been a devastating mass extinction of organisms at the end of the Ordovician. This extinction has been chronicled to be of the greatest mass extinction ever in Earth History with over 100 families going extinct. 

Reason of Extinction of Ordovician

There has been majorly 2 reasons for Ordovician going extinct:-

1. One belief was that it was the breakup and movement of the massive supercontinent into many splinters. However, modern biology makes us know that this would not possibly result in extinction; instead, it would give additional niche space for groups to expand into.

2. A greater cause is that the Earth cooled, especially the oceans where the majority of the organisms lived during the Ordovician period (Remember there are still no evidence of land plants and land organisms). All the extinctions took place in the oceans.

A pronounced extinction took place in the tropical oceans. This makes sense because if the oceans cooled off due to the development of a huge ice sheet over the south polar area, the organisms adapted to warmer tropical conditions would have limited options and feasible nowhere to migrate to. There would be restricted regions warm enough to harbour all the warm-favouring organisms. This is inclined to support the idea that cooling resulted in many of the extinctions.

Silurian Period

It is the expansion of life following the mass extinction of the Ordovician.  the first land plants appeared during the Silurian Period. Once again expanded the Marine organisms in diversity following the extinction of many families in the Late Ordovician.

The Silurian was possibly comparatively warm even though pCO₂ (Partial Pressure of Carbon Dioxide) may have been lower. This is believed to be since there has been no large landmass over the South Polar Region through the Silurian period.

Devonian Period

Devonian fish were a common element of the marine biological communities. Particularly important organisms during the Devonian were the jawed fish.

The first fossil evidence of terrestrial trees and insects appeared from Devonian age rocks. The Devonian is quite warm and the climate is thought to have been very dry. Evidence of this emerges from large amounts of tropical-like reefs and evaporite (salt deposits).

In current times, for example, evaporites are only limited to the mid-latitude belt where dry sinking air appearing from the Hadley cells makes these regions dry. During the Devonian period, these evaporite deposits were observed well beyond 30 degrees north and south.

A phyllosilicate, which was previously known as a disilicate, is a compound with a structure in which the silicate tetrahedrons are arranged in sheets. Hence, they are also known as sheet silicates. In these sheet silicates, the central atom is silicon and is surrounded by four atoms of oxygen at the corners of a tetrahedron. The sheet silicates form the parallel sheets of the silicate tetrahedra as given in the formula Si₂O₅ in a 2:5 ratio. These sheet silicates may or may not be present in hydrated form. 

Common examples of phyllosilicate or sheet silicate include mica and talc.

Silicate Mineral

A rock-forming mineral that is found to be made up of silicate groups is known as silicate minerals. It is one of the largest and most important classes of minerals and makes up approximately 90% of the Earth’s crust. Silicon dioxide (SiO₂) or silica is one of the common silicate minerals. This silica is found in nature in the form of the mineral quartz and its polymorphs. There is a wide variety of silicate minerals that are found in the crust of the Earth, with a wider range of combinations because of the processes going on for thousands of years during the formation of the Earth’s crust and the processes that are currently going on in the reworking of the crust of the Earth. Some of these processes are melting, crystallization, fractionation, metamorphism, weathering and diagenesis. 

General Structure and Main Groups of Silicate Minerals

It is clear from above that a silicate mineral is the one in which the anions are predominantly of silicon and oxygen atoms. In most forms of silicate found in the crust of the Earth, the silicon atom takes the central atom position in an ideal tetrahedron and the oxygen atoms take the corners while being covalently bonded to the central atom. Two of the adjacent tetrahedra may share a single vertex which results in a bridge-like formation in-between the two central silicon atoms of the two tetrahedra. In case there is an unpaired oxygen atom on the vertex that is bound only to a single silicon atom of a single tetrahedron, it acquires a negative charge and that negative charge is imparted to the silicate anion. 

In the above mentioned general structure, the silicon atoms present at the central positions may be replaced by other atoms of other elements but still would be bound to the four oxygen atoms present at the corners of the tetrahedron. In case the substituted atom does not form a tetravalent bond it then contributes an extra charge to the anion which then requires an extra cation. 

In mineralogy, the silicate minerals are classified into seven groups mainly depending on the structure of their silicate anion. They are given below in the following table:

The Phyllosilicate Group of Silicate Minerals

It is already mentioned that the phyllosilicate or sheet silicates are a group of silicate minerals in which the silicate anion or silicate tetrahedra are arranged in the form of a sheet with the chemical formula Si₂O₅ in the ratio of 2:5. Few images are shown below explaining the structures of phyllosilicates.

These are few examples of the sheet structure of the phyllosilicates. In these sheets, the silicon atoms are arranged at the corners of the hexagons, while the unshared oxygen atoms are commonly oriented on the same side of the sheet. As these atoms have the capability of formation of chemical bonds with different metal atoms and thus, the silicate sheets are interleaved with the layers of other elements. The different layers are stacked together thus leading to the formation of grouping with the unshared oxygen atoms toward the centre and these groups are weakly held together and thus it results in giving the phyllosilicates their distinct cleavage that is present parallel to the layers. 

Pyroclastic stream, in a volcanic emission, a fluidized combination of hot stone sections, hot gases, and captured air that moves at rapid in thick, dark to-dark, fierce mists that embrace the ground. The temperature of the volcanic gases can reach around 600 to 700 °C (1,100 to 1,300 °F). The speed of a stream regularly surpasses 100 km (60 miles) each hour and may accomplish speeds as incredible as 160 km (100 miles) each hour. 

Flows may even travel some distance uphill when they have adequate speed, which they accomplish either through the basic impacts of gravity or from the power of a sidelong impact out of the side of a detonating spring of gushing lava. Arriving at such temperatures and speeds, pyroclastic flows can be incredibly risky. Maybe the most well-known progression of this sort happened in 1902 on the French Caribbean island of Martinique, when an immense nuée ardente (“sparkling cloud”) cleared down the inclines of Mount Pelée and burned the little port city of Saint-Pierre, slaughtering everything except two of its 29,000 occupants.

Pyroclastic Flows Origin

Pyroclastic flows begin in hazardous volcanic ejections, when a drastic development of gas shreds gets away from magma into little particles, making what are known as pyroclastic pieces. (The term pyroclastic gets from the Greek pyro, signifying “fire,” and clastic, signifying “broken.”) Pyroclastic materials are characterized by their size, estimated in millimeters: dust (under 0.6 mm [0.02 inch]), debris (pieces somewhere in the range of 0.6 and 2 mm [0.02 to 0.08 inch]), ashes (parts somewhere in the range of 2 and 64 mm [0.08 and 2.5 inches], otherwise called lapilli), blocks (rakish sections more noteworthy than 64 mm), and bombs (adjusted parts more prominent than 64 mm). 

The liquid idea of a pyroclastic stream is kept up by the disturbance of its interior gases. Both the radiant pyroclastic particles and the moving dust storms that transcend them effectively free more gas. The extension of these gases represents the almost frictionless character of the stream just as its incredible versatility and dangerous force.

Pyroclastic Flow Material

The term tephra (debris) as initially characterized was an equivalent for pyroclastic materials, however it is presently utilized in the more-limited feeling of pyroclastic materials kept by falling through the air instead of those settling out of pyroclastic flows. For instance, debris particles that tumble from a high ejection cloud to frame broad layers downwind from a volcanic emission are alluded to as tephra and not as a pyroclastic stream store.

Nomenclature of Pyroclastic Flow

The nomenclature of pyroclastic flows is mind-boggling for two primary reasons. Assortments of pyroclastic flows have been named by volcanologists utilizing a few distinct dialects, bringing about a variety of terms. Likewise, the peril from pyroclastic flows is incredible to such an extent that they have only occasionally been seen during their development. Thus, the idea of the flows should be deduced from their stores instead of from direct proof, leaving plenty of space for translation. 

Ignimbrites (from the Latin for “fire downpour rocks’ ‘) are stored by pumice flows making thick arrangements of different measured pieces of permeable, froth like volcanic glass. Ignimbrites are for the most part created by huge emissions that structure calderas. Nuées ardentes store debris to obstruct estimated parts that are denser than pumice. Pyroclastic floods are low-thickness flows that leave flimsy however broad stores with cross-slept with layering. 

Debris flows leave stores known as tuff, which are made up fundamentally of debris measured pieces. Nuée ardente stores are limited essentially in valleys, while ignimbrites structure plateau-like stores that cover the past geography (the arrangement of the surface). Thick ignimbrites that were extremely hot when ejected may be minimal and unite into hard, welded tuffs.

The Earth’s crust consists of eight major elements, oxygen, silicon, aluminium, iron, calcium, sodium, potassium and magnesium. These are actually the components that make up most of the minerals. Around 90% of the Earth’s crust was composed of over 1,000 silicate minerals. The most prevalent silicate minerals in the earth’s crust are quartz. Rock Crystals weighing many tons have been found in many places. Rock Crystal is used for costume jewellery and delicate bowls and to imitate diamonds.

Crystals 

A crystal, also known as a crystalline solid, is a solid material whose components (atoms, molecules, or ions) are arranged in a closely ordered microscopic arrangement to form a crystal lattice. Crystals are a kind of solid material in which the molecules are arranged in a regular pattern. This pattern allows the substance to take on a variety of different forms. Rock crystal bonds earth and water radiation into positive energy. It cleanses the mind and soul. It also helps to dissolve energy blockages. Anyone wearing rock crystal is helped to make just, clear decisions.

Quartz

Quartz is a crystalline mineral made up of silicon and oxygen atoms that is rigid and brittle. It is composed of silicon dioxide, is a chemical compound made up of one part silicon and two parts oxygen, each oxygen atom is exchanged by two tetrahedra, giving SiO2 as the overall chemical formula. 

Formation of Crystals

The formation of crystals is known as crystallization. Crystals are formed as liquids cool and begin to harden in nature. When they try to become solid, certain molecules in the liquid congregate. This is done in a consistent and repeating sequence, resulting in the formation of crystals. As molten lava, also known as magma, cools underneath the Earth’s crust, the minerals contained within it tend to crystallize.  

Rock Crystal Quartz

Rock crystals belong to the quartz family. It is a transparent colourless variety of quartz. Rock crystal quartz forms due to the condensation of magma or lava beneath the earth’s surface, through the process of crystallization. They are used as a part to make glass and optical instruments. Quartz was used in painting and sculpture in ancient history. Quartz is mostly used in electronic applications such as mobile and navigation devices as it has electrical features and heat resistance capacity. Egyptians used quartz sand crystals to produce glass. Old artists regarded glass as a precious material, as it was rare and hard to construct.

It’s also known as the mountain crystal or Alaska gem.

Rock Crystal Stone

The quartz family includes rock crystal stone. It is colourless quartz made mostly of silicon dioxide. It is available in different forms such as colourless crystals, colourful crystals, smoky crystals, as well as microscopic and transparent forms. It combines the functions of a receiver, transmitter, and amplifier. The energy within oneself is amplified, transformed, stored, and transmitted by the rock crystal block. The rock crystal stone is ideal for clairvoyance and creativity. It also helps you to easily achieve high levels of meditation. Rock crystal can assist with energy blockages by stabilizing and harmonizing the etheric body as well as the body’s vibration rate. This stone can be used for any mineral, no matter what colour or properties they have. It amplifies its forces and energies by using its light and purity. It follows the aura and purifies it.

Different Types of Quartz Rocks

After feldspar, quartz is the second most common mineral in the Earth’s crust. About all acid igneous, metamorphic and sedimentary rocks contain it. Quartz comes in a variety of colours and shapes, some of which are semi-precious gemstones. Quartz has been the most widely used mineral in the creation of jewellery and hardstone carvings since antiquity, especially in Europe and the Middle East. Some of the varieties are mentioned below:

1. Onyx Agate 

This type of quartz has straight bands, parallel and these are consistent in size.

2. Agate 

Semi-translucent to translucent multi-coloured banded chalcedony. While agates can be found in a variety of rocks, they are most commonly associated with volcanic rocks.

3. Jasper 

It is a character in the film Jasper Cryptocrystalline quartz that is opaque and usually red to brown in colour. Iron (III) inclusions are responsible for the famous red colour. 

4. Aventurine

It is a type of mineral that is found in the sea. Translucent chalcedony with minimal shimmering inclusions (usually mica). Green aventurine is the most common colour, but it may also be orange, brown, yellow, blue, or grey. 

Conclusion

Quartz has been used throughout history in art and sculpture. It has its own history and discovery. Varieties of crystals are mentioned above with their composition.