Correct Answer: A. Plutonic rocks
Solution:
Igneous rocks are classified based on the depth at which the magma cools and solidifies.
- Plutonic Rocks (Intrusive): These rocks are formed when magma cools and crystallizes slowly at a considerable depth beneath the Earth's surface. The slow-cooling allows for the formation of large, visible crystals. Granite is a classic example.
- Hypabyssal Rocks: These form at intermediate depths, closer to the surface than plutonic rocks but not on the surface itself.
- Volcanic Rocks (Extrusive): These are formed when lava (magma that has reached the surface) cools rapidly on the Earth's surface. The rapid cooling results in very small crystals or a glassy texture. Basalt is a common example.
- Igneous Rocks: This is the broad category that includes all rocks formed from the cooling of magma or lava. While correct, "Plutonic rocks" is the more specific and accurate answer for rocks formed at great depth.
Correct Answer: A. metamorphic rock
Solution:
Quartzite is a hard, non-foliated metamorphic rock. It originates as pure quartz sandstone and is converted into quartzite through heating and pressure, usually related to tectonic compression within orogenic belts.
- Argillaceous rocks are primarily composed of clay minerals (e.g., shale).
- Calcareous rocks are mainly composed of calcium carbonate (e.g., limestone, marble).
- Igneous rocks are formed from the cooling and solidification of magma or lava.
Correct Answer: A. sedimentary rock
Solution:
Sandstone is a classic example of a clastic sedimentary rock. It is formed from sand-sized grains of minerals, rock fragments, or organic material that have been compacted and cemented together over millions of years.
Study Tip:
The Name is the Clue: Sandstone is made of sand. Sand is a type of sediment. Therefore, sandstone is a sedimentary rock.
Correct Answer: B. Dolerite
Solution:
Hypabyssal rocks are igneous rocks that are formed at a shallow depth below the Earth's surface. Their crystal size is typically between that of deep plutonic rocks and surface volcanic rocks.
- Granite is a plutonic rock, formed deep within the crust.
- Dolerite is a classic example of a hypabyssal rock, often found in sills and dikes.
- Basalt is a volcanic rock, formed from lava cooling on the surface.
Correct Answer: B. argillaceous rock
Solution:
Chemical classification of rocks is based on their primary chemical constituents.
- Argillaceous rocks are those in which clay or alumina (Al₂O₃) is the main constituent. Kaolin, also known as china clay, is almost pure kaolinite, which is a clay mineral. Therefore, it is classified as an argillaceous rock. Other examples include slate and laterite.
- Calcareous rocks have calcium carbonate (CaCO₃) as their main component, like limestone and marble.
- Siliceous rocks have silica (SiO₂) as their main component, like granite and quartzite.
Correct Answer: D. igneous and sedimentary rocks
Solution:
Gneiss is a high-grade metamorphic rock, meaning it has been subjected to intense heat and pressure. The key to this question is that Gneiss can be formed from the metamorphism of both igneous and sedimentary rocks.
- From Igneous Rocks (Orthogneiss): When an igneous rock, most commonly Granite, undergoes intense metamorphism, it transforms into Gneiss.
- From Sedimentary Rocks (Paragneiss): When a fine-grained sedimentary rock, such as Shale, is subjected to high-grade metamorphism, it can also transform into Gneiss.
While options A and C are individually correct, option D is the best and most complete answer because it correctly identifies the dual origin of Gneiss.
Study Tip:
Remember the Prefixes: Ortho- is for Gneiss from an Igneous origin (e.g., Granite). Para- is for Gneiss from a Sedimentary origin (e.g., Shale).
Correct Answer: A. sedimentary rocks
Solution:
Sedimentary rocks are defined by their formation process: the gradual deposition of sediments (particles of rock, minerals, or organic matter). Over time, layers of these sediments are compacted by pressure and cemented together to form solid rock.
- Igneous rocks are formed from the cooling of molten rock.
- Metamorphic rocks are formed when existing rocks are changed by heat and pressure.
Study Tip:
The name tells the story: "Sedimentary" rocks are made from "sediment" that has been deposited in layers.
Correct Answer: D. all the above
Solution:
For a stone to be considered good quality for construction, it must possess a combination of essential properties. All the listed options are critical requirements:
- Be durable: The stone must be hard, tough, and strong enough to withstand the forces of nature (weathering) and structural loads over a long period without deteriorating.
- Be free from clay: Clay and other soft impurities within a stone can absorb water, leading to decay, disintegration, and a loss of strength.
- Resist action of acids: Stones used in urban or industrial areas are exposed to acid rain. A good quality stone should not be easily weathered or discolored by these acidic actions.
Since all three are necessary characteristics, "all the above" is the correct choice.
Correct Answer: B. argillaceous rocks
Solution:
The chemical classification of rocks is based on their dominant mineral content. The word "argil" is another term for clay.
- Argillaceous rocks are those in which clay minerals (alumina) are the main component. Examples include slate, shale, and kaolin.
- Siliceous rocks are dominated by silica (e.g., granite, quartz).
- Calcareous rocks are dominated by calcium carbonate (e.g., limestone, marble).
Since argil means clay, rocks where it predominates are called argillaceous.
Correct Answer: C. slate
Solution:
Slate is the ideal rock for roofing due to its unique properties. It is a metamorphic rock that has perfect cleavage, meaning it can be easily split into thin, durable, and waterproof sheets. This makes it an excellent barrier against rain and snow.
- Granite and Basalt are too heavy and difficult to shape into thin tiles for roofing.
- Pumice is a volcanic rock that is very porous and lightweight, making it unsuitable for roofing as it would absorb water.
Correct Answer: D. All the above
Solution:
This question tests the understanding of selecting the right type of stone for a specific purpose. Each statement represents a correct principle in construction:
- Soft stones for carving: Intricate carvings and ornamental work require stones that are soft enough to be worked easily without fracturing.
- Light stones for arches: Reducing the self-weight of an arch is crucial for its stability. Using lighter stones helps minimize the load on the supporting abutments.
- Hard stones for high pressure: For structural elements like foundations and columns that bear significant loads, a stone with high compressive strength (a hard stone) is essential.
Since all individual statements are correct applications of stone properties, "All the above" is the correct choice.
Correct Answer: A. Granite
Solution:
Plutonic rocks are a type of intrusive igneous rock that solidifies from magma slowly cooling below the surface of the Earth.
- Granite is the most common and well-known example of a plutonic rock.
- Dolerite is a hypabyssal rock, cooling at intermediate depths.
- Basalt is a volcanic (extrusive) rock, cooling rapidly on the surface.
Correct Answer: C. metamorphic rocks
Solution:
The process described is the definition of metamorphism. Metamorphic rocks are created when existing rocks (called parent rocks) are subjected to intense heat, high pressure, or chemical alterations. This "metamorphosis" (change in form) creates a new type of rock.
- Igneous rocks are formed from cooled magma.
- Sedimentary rocks are formed from deposited sediments.
Correct Answer: A. 5%
Solution:
Water absorption is a key indicator of a stone's durability. For a high-quality building stone, the percentage of water absorbed by weight after 24 hours of immersion should be very low, ideally less than 5%. Stones with high absorption are more susceptible to damage from weathering, especially freeze-thaw cycles.
Correct Answer: C. metamorphic rock
Solution:
Marble is a classic example of a metamorphic rock. It is formed when limestone, which is a sedimentary rock, is subjected to intense heat and pressure (metamorphism). This process recrystallizes the original calcite in the limestone, forming a dense, crystalline rock.
- Stratified rock is a physical classification (describing rocks in layers) and often applies to sedimentary rocks, but "metamorphic" is the correct geological classification for marble.