CBSE Class 11 Geography Chapter 5: Minerals and Rocks NCERT Solutions

Solution: Granite is a common type of intrusive igneous rock. Its primary mineral components are feldspar and quartz. Feldspar is typically an aluminum silicate, and quartz is silicon dioxide. Therefore, the two main constituents that form the basis of granite are silica and aluminum.

The correct option is (c) Silica and aluminum.

Solution: Metamorphic rocks are formed when existing rocks are transformed by heat, pressure, or chemical reactions. A significant characteristic of many metamorphic rocks is foliation. Foliation refers to the parallel alignment of mineral grains or the banding within the rock, which develops under directed pressure. While metamorphic rocks can be crystalline, foliation is a more specific and salient feature that distinguishes many of them.

The correct option is (d) Foliation.

Solution: Single element minerals, also known as native elements, are composed of only one type of atom. Gold (Au), silver (Ag), and graphite (a form of carbon, C) are examples of native elements. Mica, however, is a complex silicate mineral group, typically containing aluminum, potassium, iron, magnesium, and other elements bonded together. Therefore, mica is not a single element mineral.

The correct option is (c) Mica.

Solution: The hardness of minerals is often measured using the Mohs scale. Diamond is known to be the hardest naturally occurring mineral, ranking 10 on the Mohs scale. Topaz ranks 8, Quartz ranks 7, and Feldspar typically ranks 6. Thus, diamond is significantly harder than the other options listed.

The correct option is (b) Diamond.

Solution: Sedimentary rocks are formed from the accumulation and cementation of sediments. Tillite is a sedimentary rock formed from compacted glacial till. Borax is a mineral that can form sedimentary deposits. Breccia is a clastic sedimentary rock composed of angular fragments. Marble, on the other hand, is a metamorphic rock formed from the recrystallization of limestone or dolomite under heat and pressure.

The correct option is (d) Marble.

Solution: Rocks can be broadly defined as naturally occurring solid aggregates of one or more minerals or mineraloids. They constitute the solid crust of the Earth. Rocks can vary greatly in hardness and texture, from hard materials like granite to softer substances like clay, gravel, or sandstone. The three major classes of rocks are:

1. Igneous rocks: Formed from the cooling and solidification of molten rock (magma or lava).
2. Sedimentary rocks: Formed from the accumulation and cementation of sediments.
3. Metamorphic rocks: Formed when existing rocks are transformed by heat, pressure, or chemical reactions.

The scientific study of rocks is called Petrology.

Solution: An igneous rock is one of the three main rock types, formed through the cooling and solidification of molten rock material. This molten material is called magma when it is beneath the Earth's surface and lava when it erupts onto the surface.

Method of Formation: Igneous rocks originate from the cooling and crystallization of magma or lava. If the cooling happens slowly deep within the Earth, large crystals can form (intrusive or plutonic igneous rocks). If the cooling happens rapidly on the Earth's surface, smaller crystals or a glassy texture results (extrusive or volcanic igneous rocks).

Characteristics:

Often composed of interlocking crystals.

Can range in texture from fine-grained (aphanitic) to coarse-grained (phaneritic) or glassy.

May contain vesicles (gas bubbles) if formed from lava.

Generally lack fossils.

Considered 'parent rocks' or 'primary rocks' because all other rock types are believed to be derived from them through various geological processes.

Solution: Sedimentary rocks are formed from the accumulation and consolidation of sediments. Sediments are particles of rock and minerals that have been broken down by weathering and erosion, or organic materials, which are then transported by agents like rivers, glaciers, wind, and ocean waves.

Mode of Formation: The process begins with the weathering and erosion of pre-existing rocks, breaking them down into smaller fragments (sediments). These sediments are then transported by various agents of denudation (like water, wind, ice) and deposited in layers at favourable locations, such as ocean basins, lake beds, or river valleys. Over time, these deposited layers are buried under more sediment. The weight of the overlying material compacts the lower layers (compaction), and dissolved minerals in the groundwater precipitate between the sediment grains, binding them together (cementation). This process transforms the loose sediments into solid sedimentary rock.

Solution: The rock cycle explains the dynamic and continuous process through which the three major types of rocks—igneous, sedimentary, and metamorphic—are transformed from one type into another over geological time. Rocks are not static; they constantly change.

The cycle illustrates that:

• Igneous rocks, formed from molten material, can be weathered and eroded to form sediments, which then form sedimentary rocks.
• Both igneous and sedimentary rocks can be subjected to intense heat and pressure deep within the Earth, transforming them into metamorphic rocks.
• Metamorphic rocks, if subjected to even higher temperatures, can melt to form magma, which then cools to create new igneous rocks.
• Sedimentary rocks can also be buried deeply, melt, and form igneous rocks.

This interconnected process shows that any rock type can eventually become any other rock type, demonstrating a fundamental relationship and continuous transformation within the Earth's crust.