Quartzite is metamorphosed from

1. Composition of the Earth's Crust (basic)

The Earth's crust is the outermost solid shell of our planet, often compared to the thin skin of an apple. Although it is the part of the Earth we live on and study most, it makes up only a tiny fraction—less than 1%—of the Earth’s total volume and mass Physical Geography by PMF IAS, Earths Interior, p.52. This layer is fundamentally brittle, meaning it tends to break or fracture under stress rather than flow like the deeper layers. Geographers and geologists study the crust because its composition and structure directly determine the landforms we see, from the deepest ocean trenches to the highest mountain peaks Certificate Physical and Human Geography GC Leong, The Earth's Crust, p.17.

The crust is not uniform; it is divided into two distinct types with very different physical and chemical personalities: Continental Crust and Oceanic Crust. The continental crust is much thicker, averaging about 30 km, but reaching up to 70–100 km beneath massive mountain ranges like the Himalayas FUNDAMENTALS OF PHYSICAL GEOGRAPHY NCERT, Interior of the Earth, p.22. In contrast, the oceanic crust is remarkably thin, averaging only about 5 km. Even though the continental crust is thicker, it is actually less dense (avg. 2.7 g/cm³) than the oceanic crust, which is why the continents "float" higher on the mantle than the ocean floors.

Feature	Continental Crust	Oceanic Crust
Thickness	Thick (30–70 km)	Thin (approx. 5 km)
Dominant Minerals	Silica & Aluminium (Sial)	Silica & Magnesium (Sima)
Rock Type	Granitic (Lighter)	Basaltic (Denser)

Chemically, the crust is enriched with lighter elements. The major elements found in the crust include Oxygen (O), Silicon (Si), Aluminium (Al), Iron (Fe), Calcium (Ca), Sodium (Na), Potassium (K), and Magnesium (Mg). Traditionally, geographers used the terms Sial (Silica + Aluminium) to describe the continental crust and Sima (Silica + Magnesium) to describe the oceanic crust Physical Geography by PMF IAS, Earths Interior, p.53. While modern science uses more complex models, these terms remain helpful for remembering that continents are dominated by lighter silicates, while the ocean floors are composed of heavier, darker basaltic rocks.

Sources: Physical Geography by PMF IAS, Earths Interior, p.52-53; FUNDAMENTALS OF PHYSICAL GEOGRAPHY NCERT, Interior of the Earth, p.22; Certificate Physical and Human Geography GC Leong, The Earth's Crust, p.17

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

In geology, nothing is permanent. The Rock Cycle is a continuous, dynamic process through which rocks are transformed from one type into another over millions of years. Think of it as nature's ultimate recycling program. It ensures that the Earth's crust is constantly being renewed and reshaped by both internal forces (like volcanic activity) and external forces (like weathering and erosion). As noted in Physical Geography by PMF IAS, Types of Rocks & Rock Cycle, p.174, this cycle explains how old rocks are systematically destroyed and reborn as new ones.

The cycle begins with Igneous rocks, often called "primary rocks" because they are the ancestors of all other rock types. When molten magma or lava cools and solidifies, igneous rocks are born. However, the story doesn't end there. Once these rocks reach the surface, they are attacked by agents of weathering like rain, wind, and ice. They break down into tiny fragments which, when compressed over ages, form Sedimentary rocks. If any rock type—be it igneous or sedimentary—is buried deep underground and subjected to intense heat and pressure, it undergoes a chemical and structural makeover to become a Metamorphic rock Certificate Physical and Human Geography, GC Leong, Chapter 2, p.19.

What makes this a true cycle is its interdependence. The process doesn't just move in one direction. For example:

• Igneous to Sedimentary: Through weathering and erosion.
• Metamorphic to Sedimentary: Even a metamorphic rock can be weathered back into fragments.
• Any rock to Magma: Through the process of subduction, crustal rocks are pushed down into the Earth's mantle, where they melt back into molten magma, eventually cooling to become igneous rocks once again Physical Geography by PMF IAS, Types of Rocks & Rock Cycle, p.174.

Process	Agent of Change	Resulting Rock Type
Cooling/Solidification	Magma/Lava cooling	Igneous
Lithification	Weathering, Deposition, Pressure	Sedimentary
Metamorphism	Intense Heat & Pressure	Metamorphic

Sources: Physical Geography by PMF IAS, Types of Rocks & Rock Cycle, p.174; Certificate Physical and Human Geography, GC Leong, Chapter 2: The Earth's Crust, p.19

3. Sedimentary Rocks: Formation and Examples (basic)

Welcome back! Now that we’ve explored the internal heat and fire of igneous rocks, let’s look at the rocks that tell the history of the Earth’s surface: Sedimentary Rocks. The name comes from the Latin word sedimentum, which literally means "settling." Unlike igneous rocks that form from cooling magma, sedimentary rocks are formed from the accumulation of debris—fragments of older rocks, minerals, or even organic remains—that settle over time in layers. This is why they are often called stratified rocks, as they appear in distinct horizontal layers or 'strata' Physical Geography by PMF IAS, Types of Rocks & Rock Cycle, p.171.

The journey from loose sand or mud to a solid rock involves a process called lithification. Think of it as a natural "compacting and cementing" process. First, denudation (weathering and erosion) breaks down existing rocks into sediments. These sediments are then transported by agents like water, wind, or ice and deposited in basins. Over millions of years, the weight of the upper layers squeezes the lower layers (compaction), and minerals acting like natural glue bind the particles together (cementation) Certificate Physical and Human Geography, GC Leong, Chapter 2, p.19. Interestingly, while these rocks cover about 75% of the Earth's land surface, they actually make up only about 5% of the total crustal volume because they are mostly found as a thin veneer on the surface Physical Geography by PMF IAS, Types of Rocks & Rock Cycle, p.171.

We classify these rocks based on how they were formed. This is a crucial distinction for your exams:

Mode of Formation	Process	Examples
Mechanically Formed	Formed from the physical accumulation of rock fragments.	Sandstone (made of quartz grains), Shale (clay), Loess (wind-blown dust).
Organically Formed	Formed from the remains of living organisms (shells, corals, plants).	Coal (vegetation), Chalk and Limestone (marine organisms), Geyserite.
Chemically Formed	Formed when minerals precipitate out of a water solution.	Halite (rock salt), Potash, and some types of Limestone.

In India, these rocks are of immense economic and geographical importance. For instance, the Indo-Gangetic plains are made of vast sedimentary accumulations, and our major energy reserves—coal—are found in the Gondwana sedimentary deposits of river basins like the Damodar and Mahanadi Physical Geography by PMF IAS, Types of Rocks & Rock Cycle, p.172.

Sources: Physical Geography by PMF IAS, Types of Rocks & Rock Cycle, p.171-172; Certificate Physical and Human Geography, GC Leong, Chapter 2: The Earth's Crust, p.19

4. Igneous Rocks: Plutonic and Volcanic (intermediate)

To understand the architecture of the Earth's crust, we must start with the 'Primary Rocks' — the Igneous rocks. These are the first rocks to form from the cooling and solidification of molten material. When this molten material is deep underground, we call it magma; once it breaks through to the surface, it is known as lava. The fundamental difference between Plutonic and Volcanic rocks lies entirely in where this cooling happens and how fast it occurs NCERT Class XI, Interior of the Earth, p.24.

Plutonic (Intrusive) Rocks are the 'slow-cooked' rocks of the interior. Because they are buried deep within the crust, they are insulated by the surrounding rock layers, which forces the magma to cool at an incredibly slow pace. This leisurely cooling gives atoms enough time to migrate and arrange themselves into large, easily-recognized crystals. A classic example is Granite. You won't see these rocks forming in real-time; they only appear on the surface after millions of years of uplift and the wearing away (denudation) of the overlying earth GC Leong, Chapter 2, p.18.

On the other hand, Volcanic (Extrusive) Rocks are formed when lava reaches the surface and is suddenly exposed to the cooler atmosphere or ocean water. This 'thermal shock' causes rapid cooling, which prevents large crystals from forming. Instead, these rocks are fine-grained or even glassy in texture. Basalt is the most famous example, covering vast areas like the Deccan Traps in India. Sometimes, basalt solidifies into striking polygonal columns, like those seen at the Giant's Causeway PMF IAS, Types of Rocks & Rock Cycle, p.170.

Feature	Plutonic (Intrusive)	Volcanic (Extrusive)
Cooling Location	Deep within the crust	At or near the surface
Cooling Rate	Very Slow	Very Rapid
Grain/Crystal Size	Large, coarse grains (e.g., Granite)	Small, fine grains (e.g., Basalt)

Sources: FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.), Interior of the Earth, p.24; Certificate Physical and Human Geography, GC Leong, Chapter 2: The Earth's Crust, p.18; Physical Geography by PMF IAS, Types of Rocks & Rock Cycle, p.170

5. Exogenic Processes: Weathering and Denudation (intermediate)

While endogenic forces like tectonics and volcanism act as the 'builders' of the Earth’s crust, exogenic forces act as the 'sculptors.' These external forces, primarily driven by solar energy and gravity, work relentlessly to level the Earth's surface through a process called gradation. This involves a dual action: degradation (the wearing down of high reliefs) and aggradation (the filling up of low-lying basins or depressions) NCERT Class XI, Geomorphic Processes, p.37. Because endogenic forces are constantly elevating new land, the exogenic processes never truly finish their job, resulting in the diverse landscapes we see today.

The primary mechanism behind this sculpting is weathering. Unlike erosion, weathering is an in-situ (on-site) process—it is the mechanical disintegration or chemical decomposition of rocks without any significant motion of the materials PMF IAS, Geomorphic Movements, p.83. We generally categorize weathering into three types:

• Physical (Mechanical) Weathering: Rocks break into smaller fragments due to temperature changes, frost action, or pressure release, without changing their chemical identity.
• Chemical Weathering: The internal structure of minerals is altered by reactions with water, oxygen, or acids. Processes include oxidation (rusting), carbonation (reaction with dissolved CO₂), and hydration PMF IAS, Geomorphic Movements, p.90.
• Biological Weathering: Living organisms like plant roots, burrowing animals, or microbes contribute to rock breakdown through both physical pressure and chemical secretions.

When we look at the bigger picture, we use the term denudation. Denudation is an umbrella term that covers the entire sequence of 'stripping off' the Earth's covering. It encompasses weathering, mass wasting (downslope movement under gravity), erosion, and transportation. Essentially, weathering prepares the rock by weakening it, and erosion (via water, wind, or ice) carries it away NCERT Class XI, Geomorphic Processes, p.37.

Feature	Weathering	Erosion
Movement	Static / In-situ (no transport)	Dynamic (involves transport)
Agents	Temperature, moisture, organisms	Running water, wind, glaciers, waves
Outcome	Weakens and fragments rock	Sculpts landforms and removes debris

Sources: FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.), Geomorphic Processes, p.37; Physical Geography by PMF IAS, Geomorphic Movements, p.83, 90

6. Mechanisms of Metamorphism (intermediate)

The word metamorphism literally translates to a 'change of form' (meta = change, morphe = form). It is a process where the original minerals within a rock undergo recrystallisation and reorganisation without the rock ever melting into magma. This is a crucial distinction: metamorphism happens in the solid state, driven by changes in Pressure (P), Volume (V), and Temperature (T) Fundamentals of Physical Geography, NCERT 2025 ed., Geomorphic Processes, p.38. When rocks are forced deep into the crust by tectonic movements or baked by rising magma, their chemical bonds break and reform into more stable structures suited for their new, high-energy environment Physical Geography by PMF IAS, Types of Rocks & Rock Cycle, p.173.

There are two primary 'styles' of metamorphism based on the dominant force at play:

Mechanism	Driving Force	Resulting Feature
Thermal (Contact)	Extreme Heat (usually from nearby magma)	Recrystallisation into hard, dense rocks (e.g., Limestone to Marble).
Dynamic (Regional)	Extreme Pressure (usually from tectonic plates colliding)	Mechanical crushing or mineral alignment (Foliation).

During these processes, minerals may align themselves in layers or lines, a phenomenon known as foliation or lineation Physical Geography by PMF IAS, Types of Rocks & Rock Cycle, p.173. For instance, the intense pressure during mountain building can transform soft shale into hard, sheet-like slate or schist. Conversely, if a rock like sandstone is baked by heat, its quartz grains fuse together to form quartzite, a rock so tough it can form the jagged peaks of great mountain ranges Certificate Physical and Human Geography, GC Leong, The Earth's Crust, p.19.

Sources: Fundamentals of Physical Geography, NCERT 2025 ed., Geomorphic Processes, p.38; 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

7. Metamorphic Pairs: Protoliths and their Products (exam-level)

In the fascinating cycle of geology, no rock is truly finished. Metamorphism is the process by which existing rocks—whether igneous or sedimentary—undergo a profound transformation in mineralogy, texture, and chemical composition due to extreme heat and pressure. The original rock from which a metamorphic rock forms is known as the protolith (or parent rock). Think of it like a piece of dough; the heat and pressure of the oven don't change its chemical essence, but they fundamentally alter its structure and appearance into bread. As noted in Certificate Physical and Human Geography, Chapter 2, p.19, these forces are particularly intense during tectonic earth movements.

One of the most classic examples is the transformation of sandstone into quartzite. Under intense thermal or regional metamorphism, the individual quartz grains and the silica cement holding them together in sandstone recrystallize. They fuse into a hard, crystalline, and non-foliated rock that is incredibly resistant to weathering. Similarly, limestone (which is primarily calcium carbonate) recrystallizes to form marble. This change is so powerful that even the fossils originally present in the limestone are usually destroyed, resulting in the beautiful, sugary texture we see in the marbles of Makrana Geography of India, Resources, p.29. Interestingly, thermal metamorphism is so pervasive that the very peak of Mount Everest consists of metamorphosed limestone Physical Geography by PMF IAS, Types of Rocks & Rock Cycle, p.173.

The transformation isn't always a simple one-to-one step. For instance, shale (a fine-grained sedimentary rock) can follow a progression based on the intensity of pressure and heat: first becoming slate, then phyllite, and eventually schist. Even igneous rocks aren't immune; the coarse-grained granite often undergoes metamorphism to become gneiss (pronounced 'nice'), characterized by distinct mineral banding. This chemical "repackaging" allows minerals to align themselves in ways that best withstand the tectonic stress being applied to them.

Protolith (Original Rock)	Metamorphic Product	Primary Characteristic
Sandstone	Quartzite	Extremely hard; high silica content
Limestone	Marble	Calcite crystals; used in architecture
Shale / Clay	Slate / Schist	Foliated (layered); splits easily
Granite	Gneiss	Banded appearance; high-grade metamorphism
Coal	Graphite	Pure carbon transition

Sources: Certificate Physical and Human Geography, Chapter 2: The Earth's Crust, p.19; Physical Geography by PMF IAS, Types of Rocks & Rock Cycle, p.173; Geography of India by Majid Husain, Resources, p.29

8. Solving the Original PYQ (exam-level)

Now that you have mastered the basics of the Rock Cycle and the process of Metamorphism, this question tests your ability to link a specific protolith (parent rock) to its metamorphic descendant. In your previous modules, we discussed how intense heat and pressure cause minerals to recrystallize without melting. The name Quartzite itself provides a linguistic clue; it is almost entirely composed of the mineral quartz. To solve this, you must recall which sedimentary rock is primarily made of quartz grains cemented together. That rock is sandstone, making (C) sandstone the only logical origin for a rock defined by its dense, silica-rich crystalline structure.

As a UPSC aspirant, you must develop the habit of active elimination by identifying the specific transformations of the other options. UPSC often uses these as traps to see if you have memorized the distinct categories of the rock cycle. For instance, Limestone (A) is composed of calcium carbonate and transforms into Marble, while Shale (D), which is clay-rich, undergoes a sequence of changes starting with Slate. Plutonic rocks (B) like granite typically metamorphose into Gneiss. By knowing these specific pairings, you can confidently isolate the arenaceous (sandy) origin of Quartzite.

This relationship is a fundamental concept explained in Certificate Physical and Human Geography, GC Leong, where the distinction between various sedimentary origins is key to understanding landforms. During the metamorphism of sandstone, the individual quartz grains and the silica cement fuse together to create a rock so hard that it often breaks through the grains rather than around them. This level of conceptual clarity is exactly what the UPSC expects when they ask you to trace the lineage of the Earth's crustal materials.