Quartizite is metamorphosed from

1. Earth's Crust and Mineral Composition (basic)

The Earth’s crust is the thin, fragile "skin" that forms the outermost layer of our planet. While it feels massive to us, it actually makes up less than 1% of the Earth's total mass and volume. Think of it as a protective shell made of various rocks that differ in texture, color, and resistance to erosion Certificate Physical and Human Geography, The Earth's Crust, p.17. The density of this layer averages around 2.7 g/cm³, which is significantly lighter than the Earth's overall average density of 5.51 g/cm³ Physical Geography by PMF IAS, Earths Interior, p.52.

The crust is not uniform; it varies significantly between the oceans and the continents. The Oceanic Crust is relatively thin (5–30 km) but denser, whereas the Continental Crust is much thicker (50–70 km) but lighter. In massive mountain ranges like the Himalayas, the continental crust can even reach depths of 70–100 km Physical Geography by PMF IAS, Earths Interior, p.52.

Feature	Continental Crust	Oceanic Crust
Thickness	Thicker (50-70 km)	Thinner (5-30 km)
Common Minerals	Silica + Aluminium (Sial)	Silica + Magnesium (Sima)
Density	Lighter	Heavier

Chemically, the crust is enriched with lighter elements like Oxygen, Silicon, and Aluminium. Geologists traditionally classified the continental crust as Sial (Silica + Aluminium) and the oceanic crust as Sima (Silica + Magnesium). This mineral composition explains the buoyancy of the continents; the lighter "Sial" essentially sits atop the denser materials below Physical Geography by PMF IAS, Earths Interior, p.53.

Sources: Certificate Physical and Human Geography, The Earth's Crust, p.17; Physical Geography by PMF IAS, Earths Interior, p.52; Physical Geography by PMF IAS, Earths Interior, p.53

2. The Rock Cycle: Interdependence of Rock Types (basic)

Think of the Earth's crust not as a static floor, but as a massive, slow-motion recycling plant. The Rock Cycle is the continuous process through which old rocks are transformed into new ones, ensuring that no rock is truly "permanent." At the heart of this cycle are Igneous rocks, often called Primary rocks because they are the first to form from molten magma. All other rock types—sedimentary and metamorphic—can eventually be traced back to these primary sources Physical Geography by PMF IAS, Types of Rocks & Rock Cycle, p.174.

The interdependence between these types is fascinating. When igneous or metamorphic rocks are exposed to the elements, they are broken down into fragments. These fragments, or sediments, accumulate over long periods (often underwater) and harden into Sedimentary rocks, characterized by their distinct layers or strata Certificate Physical and Human Geography, The Earth's Crust, p.18. However, the cycle doesn't stop there. If these sedimentary or igneous rocks are subjected to intense heat and pressure—perhaps during mountain-building movements—they undergo metamorphism. This "change of form" can completely alter their appearance and mineral structure, turning soft sandstone into hard quartzite or common limestone into elegant marble Physical Geography by PMF IAS, Types of Rocks & Rock Cycle, p.173.

Original Rock (Protolith)	Metamorphic Result	Process Driver
Sandstone (Sedimentary)	Quartzite	High Heat/Pressure
Limestone (Sedimentary)	Marble	Thermal Metamorphism
Clay/Shale (Sedimentary)	Slate/Schist	Intense Pressure
Granite (Igneous)	Gneiss	Regional Metamorphism

To close the loop, any of these rocks—igneous, sedimentary, or metamorphic—can be pushed deep into the Earth's interior through a process called subduction. Once they reach the mantle, the extreme heat melts them back into molten magma, providing the raw material for new igneous rocks to form once again Physical Geography by PMF IAS, Types of Rocks & Rock Cycle, p.174. This constant transformation explains why the Earth's surface is a complex mosaic of rocks with vastly different histories.

Sources: Physical Geography by PMF IAS, Types of Rocks & Rock Cycle, p.173-174; Certificate Physical and Human Geography, The Earth's Crust, p.18-19

3. Sedimentary Rocks: Formation and Examples (basic)

Sedimentary rocks are the Earth’s "storytellers" because they form layer by layer, often trapping fossils and climatic clues within them. The process begins with denudation—the weathering and erosion of pre-existing rocks (igneous, metamorphic, or even older sedimentary rocks). These broken-down fragments, called sediments, are transported by agents like water, wind, or ice and deposited in layers, usually in low-lying areas or water bodies. Over time, the weight of overlying layers and chemical changes lead to lithification—the process of turning loose sediments into solid rock through compaction and cementation Physical Geography by PMF IAS, Chapter 13, p.171. Because of this layering, they are often called stratified rocks, with individual layers (strata) varying in thickness from a few centimeters to many meters Certificate Physical and Human Geography, Chapter 2, p.18.

To master this topic, we classify these rocks based on their mode of formation:

• Mechanically Formed (Clastic): These are created from the physical accumulation of rock fragments. Sandstone (made of sand grains, usually quartz) and Shale (made of fine clay) are the most common. When sediments are deposited by wind, they form Loess; when deposited by glaciers, they form Tillite Physical Geography by PMF IAS, Chapter 13, p.171.
• Organically Formed: These derive from the remains of living organisms like corals, shellfish, or plants. Over time, the fleshy parts decompose, leaving behind hard shells (which form Chalk or Limestone) or carbon-rich plant matter (which forms Coal) Certificate Physical and Human Geography, Chapter 2, p.19.
• Chemically Formed: These occur when minerals precipitate out of a water solution, often due to evaporation. Halite (rock salt), potash, and certain types of limestone are formed this way Physical Geography by PMF IAS, Chapter 13, p.171.

Formation Mode	Description	Key Examples
Mechanical	Physical accumulation of debris	Sandstone, Shale, Conglomerate, Loess
Organic	Remains of plants and animals	Coal, Chalk, Limestone, Geyserite
Chemical	Precipitation from solution	Halite (Salt), Potash, Gypsum

It is a common point of confusion in exams, but remember: while sedimentary rocks cover about 75% of the Earth's land surface, they are just a thin "veneer," making up only 5% of the total volume of the Earth's crust Physical Geography by PMF IAS, Chapter 13, p.171. In the Indian context, the Vindhyan system is famous for its red sandstone, which provided the building blocks for the Red Fort, Qutub Minar, and Hawa Mahal Geography of India, Chapter: Geological Structure and formation of India, p.14.

Sources: Physical Geography by PMF IAS, Types of Rocks & Rock Cycle, p.171; Certificate Physical and Human Geography, The Earth's Crust, p.18-19; Geography of India, Geological Structure and formation of India, p.14

4. Igneous Rocks: Intrusive and Extrusive (intermediate)

To understand igneous rocks, we must start with the 'parent' material: molten rock. When this material is beneath the Earth's surface, we call it magma; once it erupts onto the surface, it is known as lava. Igneous rocks are essentially the 'Primary Rocks' of our planet, forming the foundation upon which other rocks eventually develop NCERT Class XI: Fundamentals of Physical Geography, Interior of the Earth, p.24.

The defining characteristic of an igneous rock—its texture—is determined almost entirely by its cooling rate. This leads to a fundamental classification based on the location of cooling:

• Intrusive (Plutonic) Rocks: These form when magma is trapped deep inside the Earth's crust. Because the surrounding rocks act as a thick blanket of insulation, the magma cools very slowly over thousands of years. This slow pace gives mineral atoms enough time to migrate and organize into large, coarse crystals. Granite is the quintessential example of an intrusive rock PMF IAS: Physical Geography, Volcanism, p.149.
• Extrusive (Volcanic) Rocks: These form when lava reaches the surface. Exposed to the much cooler atmosphere or ocean water, the lava solidifies rapidly. This 'sudden' cooling prevents large crystals from growing, resulting in a fine-grained or even glassy texture. Basalt, which makes up the famous Deccan Traps in India, is the most common extrusive rock PMF IAS: Physical Geography, Types of Rocks & Rock Cycle, p.170.

Cooling Rate

Feature	Intrusive (Plutonic)	Extrusive (Volcanic)
Cooling Location	Deep within the crust	On or near the surface
Slow	Rapid/Sudden
Crystal Size	Large (Coarse-grained)	Small (Fine-grained)
Example	Granite	Basalt

Chemically, many extrusive rocks like basalt are mafic, meaning they are rich in iron and magnesium (Fe and Mg) and low in silica. This makes them denser, darker in color, and highly fluid when molten, allowing them to spread over vast areas to form plateaux like the Columbia-Snake Plateau GC Leong: Certificate Physical and Human Geography, The Earth's Crust, p.18.

Sources: NCERT Class XI: Fundamentals of Physical Geography, Interior of the Earth, p.24; PMF IAS: Physical Geography, Volcanism, p.149; PMF IAS: Physical Geography, Types of Rocks & Rock Cycle, p.170; GC Leong: Certificate Physical and Human Geography, The Earth's Crust, p.18

5. Plate Tectonics and Metamorphic Environments (intermediate)

To understand how rocks change, we must look at the Earth's most powerful engine: Plate Tectonics. Metamorphism is the process where rocks are physically or chemically transformed by intense heat and pressure without melting. The most dramatic metamorphic changes occur at convergent boundaries, where tectonic plates collide. Depending on the type of crust involved, the environment for rock transformation changes significantly. In Ocean-Continent (O-C) convergence, the denser oceanic plate subducts (dives) beneath the lighter continental plate. As it descends, it carries surface sediments and rocks deep into the Earth's interior. These rocks are subjected to a 'pressure cooker' environment: rising temperatures from the mantle and immense pressure from the overlying crust. This leads to regional metamorphism, altering the rock's structure across vast areas Physical Geography by PMF IAS, Convergent Boundary, p.116. However, in Continent-Continent (C-C) convergence, such as the collision that formed the Himalayas, neither plate is dense enough to subduct deeply. Instead of diving, the plates buckle, fold, and fault. This creates massive Fold Mountains Physical Geography by PMF IAS, Convergent Boundary, p.119. The intense horizontal pressure during these collisions is a primary driver for the creation of metamorphic rocks. For example, when sandstone (a sedimentary rock) is caught in these high-pressure zones, its quartz grains recrystallize and fuse together to form Quartzite—a much harder, non-foliated metamorphic rock Certificate Physical and Human Geography, The Earth's Crust, p. 19.

Feature	O-C Convergence	C-C Convergence
Primary Action	Subduction of oceanic plate	Collision and buckling (Suturing)
Metamorphic Setting	High P-T at depth in subduction zones	Horizontal compression and crustal thickening
Landform Example	Andes, Rockies Physical Geography by PMF IAS, Convergent Boundary, p.123	Himalayas, Alps Physical Geography by PMF IAS, Convergent Boundary, p.123

Sources: Physical Geography by PMF IAS, Convergent Boundary, p.116; Physical Geography by PMF IAS, Convergent Boundary, p.119; Physical Geography by PMF IAS, Convergent Boundary, p.123; Certificate Physical and Human Geography, The Earth's Crust, p.19

6. Types of Metamorphism: Contact vs. Regional (intermediate)

Metamorphism, literally meaning 'change of form', is the process by which the mineralogy and texture of a rock are reorganized due to changes in Pressure, Volume, and Temperature (PVT). This transformation occurs without the rock melting into magma; instead, it happens in a solid state through recrystallization Physical Geography by PMF IAS, Types of Rocks & Rock Cycle, p.173. Depending on which of these agents—heat or pressure—dominates and the scale at which they act, we categorize metamorphism into two primary types: Contact and Regional.

Contact Metamorphism (also known as Thermal Metamorphism) occurs when rocks come into direct contact with intense heat, usually from a magmatic intrusion. Imagine a hot iron being placed on a piece of fabric; only the area touched by the iron changes. Similarly, when molten magma rises through the crust, it 'bakes' the surrounding rocks. Because temperature is the primary driver here, the resulting rocks are often non-foliated (lacking layers). A classic example is sandstone recrystallizing into quartzite or limestone turning into marble Certificate Physical and Human Geography (GC Leong), The Earth's Crust, p.19. Interestingly, the peak of Mount Everest actually consists of metamorphosed limestone created through such thermal processes Physical Geography by PMF IAS, Types of Rocks & Rock Cycle, p.173.

Regional Metamorphism, by contrast, happens over vast areas and is driven by both high pressure and high temperature. This typically occurs during orogeny (mountain building), where tectonic plates collide and bury rocks deep within the Earth's crust Geography Class XI NCERT, Geomorphic Processes, p.38. The immense directional pressure causes minerals to align in parallel layers or bands, a texture known as foliation. This is why regional metamorphic rocks like slate, schist, and gneiss often look striped or layered. For instance, the Bengal Gneiss found in the Eastern Ghats is highly foliated due to these intense tectonic forces Geography of India (Majid Husain), Geological Structure and formation of India, p.4.

Feature	Contact Metamorphism	Regional Metamorphism
Primary Agent	Extreme Heat (Magma)	Pressure + Heat (Tectonics)
Scale	Local (near intrusions)	Large-scale (mountain ranges)
Texture	Non-foliated (Massive)	Foliated (Layered/Banded)
Examples	Quartzite, Marble	Slate, Schist, Gneiss

Sources: Physical Geography by PMF IAS, Types of Rocks & Rock Cycle, p.173; Certificate Physical and Human Geography (GC Leong), The Earth's Crust, p.19; Geography Class XI NCERT, Geomorphic Processes, p.38; Geography of India (Majid Husain), Geological Structure and formation of India, p.4

7. Protoliths and Metamorphic Transformation Pairs (exam-level)

In the study of geology, every metamorphic rock has an "ancestor" known as a protolith (from the Greek proto meaning first and lithos meaning rock). When a pre-existing rock—whether it is igneous, sedimentary, or even an older metamorphic rock—is subjected to intense heat, pressure, or chemically active fluids, it undergoes a transformation in its mineralogy and texture without melting. This process of recrystallization creates a new rock with entirely different physical properties, even though the chemical composition often remains similar to its parent Certificate Physical and Human Geography, Chapter 2: The Earth's Crust, p.19.

One of the most distinct transformations is the birth of Quartzite. Its protolith is Sandstone, a sedimentary rock rich in quartz grains. Under high temperatures and pressures, the individual quartz grains in the sandstone do not just stick together; they fuse and recrystallize into an interlocking mosaic of quartz crystals. This makes quartzite incredibly hard and resistant to weathering. Unlike sandstone, which might feel gritty, a freshly broken piece of quartzite will have a smooth, glassy appearance because the break occurs through the quartz grains rather than around them Physical Geography by PMF IAS, Chapter 13: Types of Rocks & Rock Cycle, p.174.

Understanding these "transformation pairs" is essential for identifying the geological history of a region. For instance, in India’s Papaghani river valley, we see clear evidence of magma intrusions (dykes and sills) providing the necessary heat to turn limestone into marble and sandstone into quartzite Geography of India, Geological Structure and formation of India, p.14. Below is a summary of the key pairs you should master for the exam:

Protolith (Original Rock)	Metamorphic Result	Primary Factor
Sandstone	Quartzite	Heat / Pressure
Limestone / Chalk	Marble	Heat
Shale / Clay	Slate → Schist	Pressure / Heat
Granite	Gneiss	Pressure
Coal	Graphite	Heat

Sources: Certificate Physical and Human Geography, Chapter 2: The Earth's Crust, p.19; Physical Geography by PMF IAS, Chapter 13: Types of Rocks & Rock Cycle, p.174; Geography of India, Geological Structure and formation of India, p.14

8. Solving the Original PYQ (exam-level)

You’ve just mastered how metamorphic rocks form through the recrystallization of pre-existing rocks under extreme heat and pressure. This question tests your ability to identify the protolith (parent rock) for specific metamorphic outcomes. Since Quartzite is characterized by its high silica content and interlocking quartz crystals, you must look for a parent rock that is predominantly composed of quartz grains to satisfy the chemical consistency required during metamorphism.

The logical choice is (C) Sandstone. During the process of thermal or regional metamorphism, the individual sand grains in sandstone fuse together to create a much harder, non-foliated rock. This transition from a granular texture to a crystalline one is a classic example of how mineral composition remains consistent while the physical structure is transformed. As explained in Certificate Physical and Human Geography by GC Leong, the fusion of quartz grains into an interlocking fabric is what gives quartzite its signature durability compared to its parent sandstone.

Understanding why the other options are incorrect is crucial for avoiding UPSC traps. Limestone is the parent rock for Marble, which is a common confusion point because both are non-foliated metamorphic rocks, but their mineral chemistry (calcite vs. silica) is entirely different. Shale, being a fine-grained clay-rich rock, undergoes a sequence of changes starting with Slate and Phyllite. Finally, Obsidian is an extrusive igneous rock (volcanic glass) and does not serve as the precursor to quartzite. By isolating the mineralogical link—quartz grains to quartzite—you can confidently arrive at the correct answer.