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Maharashtra HSC Geology (MSBSHSE) study materials
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Maharashtra HSC Geology (MSBSHSE) practice questions

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Question 1Earth as a Planet: Origin, Interior and Geological Time

According to the widely accepted nebular hypothesis, the Solar System formed from which material?

  1. Molten lava erupted from an early Earth
  2. A rotating cloud of gas and dust that contracted under gravity Correct answer.
  3. A collision between two pre-existing stars
  4. Fragments ejected from a passing comet

Explanation

The nebular hypothesis holds that a slowly rotating interstellar cloud of gas and dust collapsed gravitationally, flattened into a disc, and condensed into the Sun and planets. This explains the near-circular, coplanar orbits and the Sun's central mass dominance.

Question 2Earth as a Planet: Origin, Interior and Geological Time

The boundary separating the crust from the mantle is identified by a sharp increase in the velocity of which seismic waves?

  1. Rayleigh waves
  2. Surface waves
  3. P-waves Correct answer.
  4. Love waves

Explanation

The Mohorovicic discontinuity is marked by an abrupt jump in P-wave velocity as seismic energy passes from crustal rock into denser mantle rock. Surface waves travel along the surface only and are not used to define internal boundaries.

Question 3Earth as a Planet: Origin, Interior and Geological Time

Which layer of the Earth's interior is inferred to behave as a liquid because S-waves cannot pass through it?

  1. Lower mantle
  2. Inner core
  3. Outer core Correct answer.
  4. Asthenosphere

Explanation

S-waves require shear strength to propagate, so their disappearance beyond about 103 degrees from the epicentre indicates a liquid outer core. The inner core is solid and the asthenosphere is only partially molten, so both still transmit shear waves.

Question 4Earth as a Planet: Origin, Interior and Geological Time

Which radioactive decay scheme is most commonly used to date very old Archean rocks of the Deccan region's basement?

  1. Uranium-238 to lead-206 Correct answer.
  2. Rubidium-87 to strontium-87
  3. Potassium-40 to argon-40
  4. Carbon-14 to nitrogen-14

Explanation

The uranium-lead system has a half-life of about 4.5 billion years, making it suitable for dating rocks of Archean age. Carbon-14 is useful only for materials younger than roughly 50,000 years and cannot resolve such ancient ages.

Question 5Earth as a Planet: Origin, Interior and Geological Time

The principle stating that in an undisturbed sequence each layer is younger than the one below it is called the principle of:

  1. Faunal succession
  2. Cross-cutting relationships
  3. Original horizontality
  4. Superposition Correct answer.

Explanation

The principle of superposition states that sedimentary layers are deposited in order, so the lowest layer is oldest. This follows directly from the way sediment accumulates on a depositional surface.

Question 6Earth as a Planet: Origin, Interior and Geological Time

The Earth's magnetic field is believed to be generated mainly by:

  1. Charged particles trapped in the magnetosphere
  2. Convection of molten iron in the outer core Correct answer.
  3. Permanent magnetisation of the crust
  4. Electrical currents in the ionosphere

Explanation

The geodynamo model attributes the main field to convecting, electrically conducting liquid iron in the outer core. Motion of this fluid generates electric currents that sustain the magnetic field.

Question 7Earth as a Planet: Origin, Interior and Geological Time

Which eon of the Precambrian is characterised by the first appearance of abundant stromatolites and the rise of atmospheric oxygen?

  1. Hadean
  2. Phanerozoic
  3. Archean
  4. Proterozoic Correct answer.

Explanation

The Proterozoic eon records the Great Oxidation Event and widespread stromatolite reefs built by cyanobacteria. Oxygen accumulation in the atmosphere changed surface chemistry and enabled later complex life.

Question 8Earth as a Planet: Origin, Interior and Geological Time

The Deccan Traps of Maharashtra were formed mainly during which period of the geological time scale?

  1. Miocene
  2. Jurassic
  3. Permian
  4. Cretaceous-Paleogene boundary Correct answer.

Explanation

The bulk of the Deccan flood basalt volcanism occurred close to the Cretaceous-Paleogene boundary, around 66 million years ago. This timing places the traps near the end-Cretaceous mass extinction.

Question 9Earth as a Planet: Origin, Interior and Geological Time

If a mineral sample contains 25 percent of its original parent isotope, how many half-lives have elapsed?

  1. Three
  2. Two Correct answer.
  3. One
  4. Four

Explanation

After each half-life the parent fraction halves: 50 percent after one, 25 percent after two, and 12.5 percent after three. A remaining parent fraction of 25 percent therefore corresponds to two half-lives.

Question 10Earth as a Planet: Origin, Interior and Geological Time

A seismic station records P-waves but no S-waves from a distant earthquake. What does this most directly indicate about the ray path?

  1. The recording instrument was faulty
  2. The ray passed through the liquid outer core Correct answer.
  3. The waves travelled only through the crust
  4. The earthquake was too shallow to generate S-waves

Explanation

S-waves cannot propagate through a liquid, so their absence at suitable distances indicates that the ray path crossed the liquid outer core. P-waves continue through the core and are still recorded.

Question 11Earth as a Planet: Origin, Interior and Geological Time

A geologist finds a dyke cutting across a sequence of folded sedimentary beds. Which statement about relative ages is correct?

  1. The dyke is older than the folding but younger than the beds
  2. The beds are younger than the dyke
  3. The dyke and the beds are of the same age
  4. The dyke is younger than both the beds and the folding Correct answer.

Explanation

The principle of cross-cutting relationships states that a feature cutting across others must be younger than the features it cuts. Because the dyke cuts the already folded beds, it postdates both deposition and folding.

Question 12Earth as a Planet: Origin, Interior and Geological Time

Which observation best supports the idea that the Earth's inner core is solid rather than liquid?

  1. P-waves are refracted and reflected at the inner core boundary Correct answer.
  2. The outer core produces a magnetic field
  3. Surface waves have low velocity
  4. S-waves are recorded on the far side of the Earth

Explanation

Reflections and refractions of P-waves at the inner core boundary, together with a velocity increase, indicate a solid inner core. These observations also help define the inner core's radius and density.

Question 13Earth as a Planet: Origin, Interior and Geological Time

The lithosphere differs from the asthenosphere chiefly because the lithosphere is:

  1. Rigid and capable of brittle fracture Correct answer.
  2. Composed entirely of liquid rock
  3. Richer in iron and nickel
  4. Hotter and more ductile

Explanation

The lithosphere is the rigid outer shell that behaves elastically and fractures, while the asthenosphere beneath it is hotter and deforms ductilely. This contrast allows plates to move over the asthenosphere.

Question 14Earth as a Planet: Origin, Interior and Geological Time

The average geothermal gradient in the Earth's crust is approximately:

  1. 250 degrees Celsius per kilometre
  2. 25 degrees Celsius per kilometre Correct answer.
  3. 1 degree Celsius per kilometre
  4. 100 degrees Celsius per kilometre

Explanation

The crustal geothermal gradient averages about 25 degrees Celsius per kilometre, though it varies with tectonic setting. This is why deep mines and boreholes become noticeably hotter with depth.

Question 15Earth as a Planet: Origin, Interior and Geological Time

Which evidence first demonstrated that the Earth's magnetic field has reversed polarity in the past?

  1. Striped magnetic anomalies parallel to mid-ocean ridges Correct answer.
  2. The variation of magnetic declination with latitude
  3. The aurora borealis
  4. The presence of magnetic minerals in Deccan basalts

Explanation

Symmetrical magnetic stripes on either side of mid-ocean ridges record alternating normal and reversed polarity during sea-floor spreading. This provided the key proof of geomagnetic reversals.

Question 16Earth as a Planet: Origin, Interior and Geological Time

A rock sample yields a uranium-lead age of 2,000 million years. Which statement is most appropriate?

  1. The rock is younger than the Deccan Traps
  2. The rock crystallised about 2,000 million years ago Correct answer.
  3. The rock must be of sedimentary origin
  4. The rock formed during the Phanerozoic

Explanation

A radiometric age of 2,000 million years dates the crystallisation or closure of the mineral system to that time. This places the rock in the Paleoproterozoic, long before Phanerozoic and Deccan Trap times.

Question 17Earth as a Planet: Origin, Interior and Geological Time

The main reason the Earth became a layered planet with a dense core is:

  1. Density-driven separation of molten material under gravity Correct answer.
  2. The Moon's gravity pulled heavy elements inward
  3. Meteorite impacts arranged layers from outside inward
  4. Cooling of the surface caused shrinking into layers

Explanation

During early differentiation, dense metallic iron and nickel sank toward the centre while lighter silicates rose. This gravitational separation produced the core, mantle, and crust.

Question 18Earth as a Planet: Origin, Interior and Geological Time

Which of the following correctly orders the units of the geological time scale from largest to smallest?

  1. Period, era, eon, epoch
  2. Epoch, period, era, eon
  3. Eon, era, period, epoch Correct answer.
  4. Era, eon, period, epoch

Explanation

The hierarchy of geological time units runs from eon to era to period to epoch, each nested within the larger unit. This order is standard in the geological time scale.

Question 19Earth as a Planet: Origin, Interior and Geological Time

The fossil record shows that the earliest convincing evidence of life on Earth dates to approximately:

  1. 4,500 million years ago
  2. 541 million years ago
  3. 66 million years ago
  4. 3,500 million years ago Correct answer.

Explanation

Microfossils and chemical signatures in Archean rocks, together with stromatolites, indicate life by about 3,500 million years ago. This predates the Phanerozoic by nearly three billion years.

Question 20Earth as a Planet: Origin, Interior and Geological Time

A sample contains equal amounts of parent and daughter isotopes. If the half-life is 500 million years, the age of the sample is:

  1. 250 million years
  2. 1,000 million years
  3. 2,000 million years
  4. 500 million years Correct answer.

Explanation

Equal parent and daughter amounts mean half of the original parent has decayed, which corresponds to exactly one half-life. With a half-life of 500 million years, the age is 500 million years.

Question 21Earth as a Planet: Origin, Interior and Geological Time

Which statement best explains why the Earth's core is composed mainly of iron and nickel?

  1. These dense metals sank during early melting and differentiation Correct answer.
  2. Silicate minerals are denser than metals
  3. Iron and nickel were the most abundant elements in the solar nebula
  4. Iron and nickel were delivered only by late comets

Explanation

Iron and nickel are dense and were mobile during early melting, so they segregated downward to form the core. The lighter silicates remained in the mantle and crust.

Question 22Earth as a Planet: Origin, Interior and Geological Time

The discovery that P-wave velocities increase sharply at a depth of about 2,900 km marks which boundary?

  1. Lehmann discontinuity
  2. Gutenberg discontinuity Correct answer.
  3. Mohorovicic discontinuity
  4. Conrad discontinuity

Explanation

The Gutenberg discontinuity at roughly 2,900 km depth separates the mantle from the outer core and is marked by a drop in P-wave velocity and the disappearance of S-waves. The Moho lies much shallower at the crust-mantle boundary.

Question 23Earth as a Planet: Origin, Interior and Geological Time

A geologist correlates two separated sedimentary sections using an index fossil that is restricted to a short time interval and is widespread. This method relies primarily on the principle of:

  1. Isostasy
  2. Original horizontality
  3. Uniformitarianism
  4. Faunal succession Correct answer.

Explanation

The principle of faunal succession holds that fossil assemblages change in a recognisable order, so a short-ranging widespread species can identify a specific time interval. This allows correlation of strata across separated areas.

Question 24Earth as a Planet: Origin, Interior and Geological Time

Which combination of observations provides the strongest evidence for a liquid outer core and a solid inner core?

  1. Absence of S-waves beyond 103 degrees and reflected P-waves from the inner core boundary Correct answer.
  2. Occurrence of earthquakes and volcanic eruptions
  3. Magnetic reversals recorded in lavas
  4. Presence of surface waves and low heat flow

Explanation

The S-wave shadow zone shows that shear waves cannot pass through the outer core, while P-wave reflections at the inner core boundary indicate a solid inner core. Together these observations define the two-part core.

Question 25Earth as a Planet: Origin, Interior and Geological Time

The Hadean eon is poorly represented in the rock record mainly because:

  1. The eon is too recent to have preserved rocks
  2. No rocks existed anywhere on Earth at that time
  3. Intense impacts and recycling destroyed most early crust Correct answer.
  4. Rocks of that age are all buried under the Deccan Traps

Explanation

Heavy bombardment and subsequent tectonic recycling destroyed most Hadean crust, leaving only rare zircon grains and small remnants. This makes the Hadean the least well preserved part of Earth history.

Question 26Earth as a Planet: Origin, Interior and Geological Time

Which layer of the Earth's interior lies directly beneath the Mohorovicic discontinuity?

  1. The crust
  2. The outer core
  3. The asthenosphere
  4. The upper mantle Correct answer.

Explanation

The Mohorovicic discontinuity (Moho) marks the boundary where seismic P-wave velocities jump abruptly to about 8 km/s, separating the crust above from the mantle below. The material immediately beneath this boundary is the uppermost part of the mantle, not the crust. The asthenosphere and outer core lie much deeper.

Question 27Earth as a Planet: Origin, Interior and Geological Time

According to the nebular hypothesis, the terrestrial planets formed close to the Sun mainly because in the inner solar nebula:

  1. only refractory materials could condense as solids Correct answer.
  2. gravity was too weak to gather any material
  3. solar wind had already ceased
  4. volatile ices could condense readily

Explanation

In the hot inner region of the solar nebula, temperatures were too high for water, ammonia and methane ices to condense, so only refractory substances such as silicates, metal oxides and iron could exist as solids. Accretion of these dense, rocky materials produced the small, high-density terrestrial planets. The giant planets formed farther out where ices could condense.

Question 28Earth as a Planet: Origin, Interior and Geological Time

A granite pluton intrudes folded schist and is itself cut by an undeformed basaltic dyke. Using the principles of relative dating, which sequence is most defensible?

  1. Intrusion of the granite, then folding of the schist, then intrusion of the dyke
  2. Intrusion of the dyke, then folding of the schist, then intrusion of the granite
  3. Folding of the schist, then intrusion of the dyke, then intrusion of the granite
  4. Folding of the schist, then intrusion of the granite, then intrusion of the dyke Correct answer.

Explanation

The folded schist must have existed and been deformed before the granite could intrude it, so folding precedes granite emplacement. Because the undeformed dyke cuts across the granite, the dyke is younger than the granite. This gives the order: folding, granite, dyke.

Question 29Earth as a Planet: Origin, Interior and Geological Time

A basalt flow yields a potassium-argon (K-Ar) age of 60 million years, but the flow is stratigraphically sandwiched between two fossil-bearing sedimentary beds. Which interpretation is most appropriate?

  1. The K-Ar age cannot constrain the sediments at all
  2. The sedimentary beds are exactly 60 million years old
  3. The sediments must be younger than 60 Ma on both sides
  4. The sediments are older than 60 Ma below and younger than 60 Ma above Correct answer.

Explanation

Radiometric dating of an interbedded lava flow gives the age of the flow itself, which by superposition is younger than the beds beneath it and older than the beds above it. The sediments are therefore only bracketed, not dated exactly. This is the standard use of volcanic ash or lava layers as time markers in stratigraphy.

Question 30Earth as a Planet: Origin, Interior and Geological Time

S-waves from a large earthquake are not recorded beyond about 103 degrees from the epicentre, while P-waves reappear beyond about 142 degrees. Which model of the deep Earth best explains both observations together?

  1. A completely molten core in which both P-waves and S-waves travel freely
  2. A rigid mantle with no low-velocity layer anywhere beneath the crust
  3. A solid inner core surrounded by a liquid outer core that blocks S-waves and refracts P-waves into a shadow zone Correct answer.
  4. A crust that is thicker beneath the oceans than beneath the continents

Explanation

S-waves cannot pass through a liquid, so their absence beyond about 103 degrees requires a liquid outer core. P-waves crossing into the outer core are refracted, producing a P-wave shadow zone between roughly 103 and 142 degrees, after which they re-emerge through the solid inner core. Together these define a liquid outer core enclosing a solid inner core.

Question 31Mineralogy: Crystal Systems, Physical Properties and Silicate Structures

In the crystallographic axial system, which crystal system is defined by three mutually perpendicular axes that are all of equal length?

  1. Orthorhombic
  2. Isometric (cubic) Correct answer.
  3. Trigonal
  4. Tetragonal

Explanation

The isometric system requires a1 = a2 = a3 with all interaxial angles at 90 degrees, giving the highest symmetry of the seven systems. Tetragonal and orthorhombic also have 90-degree angles but unequal axial lengths, while trigonal axes are not mutually perpendicular in the same way.

Question 32Mineralogy: Crystal Systems, Physical Properties and Silicate Structures

A mineral specimen shows two cleavages meeting at 90 degrees and a third cleavage also at right angles to both. Which mineral most likely shows this cleavage pattern?

  1. Muscovite
  2. Calcite
  3. Halite Correct answer.
  4. Quartz

Explanation

Halite has cubic cleavage: three cleavages mutually at right angles because of its isometric NaCl structure. Muscovite shows one perfect basal cleavage, calcite shows three rhombohedral cleavages at about 75 degrees, and quartz shows no true cleavage.

Question 33Mineralogy: Crystal Systems, Physical Properties and Silicate Structures

On the Mohs scale, which mineral scratches fluorite but is itself scratched by orthoclase?

  1. Apatite Correct answer.
  2. Corundum
  3. Gypsum
  4. Topaz

Explanation

Apatite has hardness 5, so it scratches fluorite (4) and is scratched by orthoclase (6). Gypsum (2) cannot scratch fluorite, while topaz (8) and corundum (9) are both harder than orthoclase.

Question 34Mineralogy: Crystal Systems, Physical Properties and Silicate Structures

The basic building block of all silicate minerals is which structural unit?

  1. The alumina octahedron
  2. The carbonate triangle
  3. The silica tetrahedron Correct answer.
  4. The sulphate tetrahedron

Explanation

Silicate structures are built from the SiO4 tetrahedron, in which one silicon atom is coordinated by four oxygen atoms. Carbonate and sulphate groups contain carbon and sulphur respectively, and the alumina octahedron is a coordination polyhedron in phyllosilicates rather than the fundamental silicate unit.

Question 35Mineralogy: Crystal Systems, Physical Properties and Silicate Structures

Which silicate structure type is characterised by single chains of linked SiO4 tetrahedra?

  1. Inosilicate Correct answer.
  2. Nesosilicate
  3. Phyllosilicate
  4. Tectosilicate

Explanation

Inosilicates include single-chain silicates such as pyroxenes and double-chain silicates such as amphiboles. Nesosilicates have isolated tetrahedra, phyllosilicates have sheets, and tectosilicates have three-dimensional frameworks.

Question 36Mineralogy: Crystal Systems, Physical Properties and Silicate Structures

A mineral is soft, has a greasy feel, and leaves a white streak on a plate. Which physical property is being directly described by the greasy feel?

  1. Lustre Correct answer.
  2. Taste
  3. Tenacity
  4. Habitus

Explanation

Greasy feel is a variety of lustre, describing how light is reflected from the mineral surface. Tenacity describes behaviour under stress, taste is a chemical sense property, and habitus refers to the crystal's overall shape.

Question 37Mineralogy: Crystal Systems, Physical Properties and Silicate Structures

Which of the following minerals is a common dark-coloured ferromagnesian silicate found in basalt?

  1. Muscovite
  2. Quartz
  3. Orthoclase
  4. Augite Correct answer.

Explanation

Augite is a clinopyroxene, a ferromagnesian inosilicate that is a major mafic mineral in basalt. Orthoclase, quartz and muscovite are felsic minerals and are typically light coloured.

Question 38Mineralogy: Crystal Systems, Physical Properties and Silicate Structures

Which crystal system is represented by a mineral with three equal axes inclined at 60 degrees to each other and a vertical axis perpendicular to them?

  1. Monoclinic
  2. Hexagonal Correct answer.
  3. Isometric
  4. Triclinic

Explanation

The hexagonal system has three horizontal axes of equal length intersecting at 60 degrees, with a vertical c-axis perpendicular to them. Monoclinic and triclinic axes are unequal and inclined differently, and isometric requires perpendicular equal axes.

Question 39Mineralogy: Crystal Systems, Physical Properties and Silicate Structures

A mineral shows two sets of cleavage planes intersecting at about 56 and 124 degrees. Which mineral is most consistent with this measurement?

  1. Amphibole Correct answer.
  2. Pyroxene
  3. Halite
  4. Galena

Explanation

Amphiboles typically show two cleavages at approximately 56 and 124 degrees, reflecting their double-chain structure. Pyroxenes show cleavages near 87 and 93 degrees, while halite and galena show cubic cleavage at 90 degrees.

Question 40Mineralogy: Crystal Systems, Physical Properties and Silicate Structures

What is the coordination number of silicon in the SiO4 tetrahedron, and how does this relate to Pauling's first rule?

  1. 4, because the radius ratio of Si to O allows fourfold coordination Correct answer.
  2. 2, because each oxygen bonds to only one silicon
  3. 6, because silicon fits an octahedral site
  4. 8, because silicon is a large cation

Explanation

Each silicon is surrounded by four oxygens, giving a coordination number of 4, consistent with the radius ratio of Si to O. Pauling's first rule states that the coordination number is determined by the ratio of cation to anion radii.

Question 41Mineralogy: Crystal Systems, Physical Properties and Silicate Structures

Which statement correctly distinguishes the double-chain amphibole structure from the single-chain pyroxene structure?

  1. Amphiboles share two oxygen atoms per tetrahedron between chains, giving a 2:11 silicon-to-oxygen ratio Correct answer.
  2. Amphiboles have isolated tetrahedra joined only by cations
  3. Amphiboles contain no silicon-oxygen bonds
  4. Pyroxenes have sheet structures while amphiboles have frameworks

Explanation

In amphiboles two chains are linked by sharing oxygens, giving the ideal ratio Si4O11 per formula unit, whereas pyroxenes have single chains with Si2O6. The double chain also creates the characteristic 56 and 124 degree cleavage.

Question 42Mineralogy: Crystal Systems, Physical Properties and Silicate Structures

A crystal shows a sixfold axis of symmetry and a horizontal mirror plane. Which symmetry element is present in the hexagonal system?

  1. A fourfold inversion axis only
  2. No rotation axes, only a centre of symmetry
  3. A sixfold rotation axis perpendicular to a mirror plane Correct answer.
  4. A threefold screw axis parallel to the c-axis only

Explanation

The hexagonal system is defined by a sixfold rotation axis, often perpendicular to a horizontal mirror plane. Fourfold inversion axes belong to the tetragonal and isometric systems, and a centre of symmetry alone does not define a crystal system.

Question 43Mineralogy: Crystal Systems, Physical Properties and Silicate Structures

Which mineral is a tectosilicate with a three-dimensional framework of SiO4 tetrahedra and no cleavage?

  1. Talc
  2. Biotite
  3. Olivine
  4. Quartz Correct answer.

Explanation

Quartz is a framework silicate in which every oxygen is shared between tetrahedra, giving a rigid three-dimensional structure with no cleavage. Olivine is a nesosilicate, biotite is a phyllosilicate, and talc is also a phyllosilicate.

Question 44Mineralogy: Crystal Systems, Physical Properties and Silicate Structures

A mineral specimen is black, has a metallic lustre, and leaves a grey-black streak. Which property is most diagnostic for identifying it as magnetite rather than hematite?

  1. Low specific gravity
  2. Perfect basal cleavage
  3. Reddish-brown streak
  4. Strong attraction to a magnet Correct answer.

Explanation

Magnetite is strongly magnetic, which distinguishes it from hematite. Hematite gives a reddish-brown streak, while magnetite gives a black streak and is not characterised by perfect basal cleavage or low density.

Question 45Mineralogy: Crystal Systems, Physical Properties and Silicate Structures

Which silicate mineral group contains isolated SiO4 tetrahedra linked only by interstitial cations?

  1. Nesosilicates Correct answer.
  2. Cyclosilicates
  3. Tectosilicates
  4. Sorosilicates

Explanation

Nesosilicates contain independent SiO4 tetrahedra held together by cations such as Mg and Fe, as in olivine and garnet. Sorosilicates share one oxygen between paired tetrahedra, cyclosilicates form rings, and tectosilicates form frameworks.

Question 46Mineralogy: Crystal Systems, Physical Properties and Silicate Structures

A crystal has three unequal axes, one of which is inclined to the other two, which are perpendicular to each other. Which system does this describe?

  1. Triclinic
  2. Tetragonal
  3. Monoclinic Correct answer.
  4. Orthorhombic

Explanation

Monoclinic crystals have three unequal axes with one inclined axis and two mutually perpendicular axes. Triclinic has all three axes inclined, orthorhombic has all three perpendicular, and tetragonal has two equal axes.

Question 47Mineralogy: Crystal Systems, Physical Properties and Silicate Structures

Which physical property describes a mineral's resistance to being scratched, and which mineral defines hardness 7 on the Mohs scale?

  1. Cleavage; calcite
  2. Fracture; topaz
  3. Tenacity; garnet
  4. Hardness; quartz Correct answer.

Explanation

Hardness measures resistance to scratching, and quartz defines position 7 on the Mohs scale. Tenacity refers to behaviour under stress, cleavage to breakage along planes, and fracture to irregular breakage.

Question 48Mineralogy: Crystal Systems, Physical Properties and Silicate Structures

Which of the following best explains why graphite is much softer than diamond despite both being made of carbon?

  1. Graphite has a higher density than diamond
  2. Graphite has a layered structure with weak van der Waals bonds between sheets Correct answer.
  3. Diamond contains ionic bonds while graphite contains covalent bonds
  4. Diamond has a lower melting point than graphite

Explanation

Graphite consists of strongly bonded hexagonal sheets held together by weak van der Waals forces, so the sheets slide easily. Diamond has a rigid three-dimensional covalent framework, making it the hardest natural mineral.

Question 49Mineralogy: Crystal Systems, Physical Properties and Silicate Structures

Which mineral shows a rhombohedral cleavage with three planes inclined at about 75 degrees, and what does this reveal about its structure?

  1. Halite, reflecting its cubic structure
  2. Calcite, reflecting its trigonal carbonate structure Correct answer.
  3. Gypsum, reflecting its monoclinic structure
  4. Quartz, reflecting its framework structure

Explanation

Calcite has three cleavage directions that follow the rhombohedral carbonate structure, giving angles near 75 degrees. Halite shows cubic cleavage, quartz shows no cleavage, and gypsum shows one perfect cleavage.

Question 50Mineralogy: Crystal Systems, Physical Properties and Silicate Structures

Which phyllosilicate mineral is characterised by a perfect basal cleavage producing thin, flexible, elastic sheets and is colourless in thin section?

  1. Chlorite
  2. Muscovite Correct answer.
  3. Biotite
  4. Kaolinite

Explanation

Muscovite is a dioctahedral white mica with perfect basal cleavage and elastic sheets. Biotite is dark and iron-rich, chlorite is green, and kaolinite occurs as earthy masses rather than elastic sheets.