All questions of Rocks for Grade 2 Exam

Explanation:
A hard rock is a type of rock that has a high resistance to scratching and abrasion. It is characterized by its strong and durable nature. While all of the options given (granite, marble, diamond, and graphite) are types of rocks, only one of them is not considered a hard rock.

Granite:
Granite is a type of igneous rock that is formed from cooled and solidified magma or lava. It is composed mainly of quartz, feldspar, and mica. Granite is known for its durability and strength, making it a popular choice for construction and countertops.

Marble:
Marble is a metamorphic rock that is formed from limestone under heat and pressure. It is composed mainly of calcite or dolomite minerals. Marble is prized for its beauty and is often used in sculptures, building materials, and decorative purposes. While marble is relatively soft compared to other rocks, it is still considered a hard rock.

Diamond:
Diamond is a mineral composed of carbon atoms arranged in a crystal lattice structure. It is the hardest known natural substance, scoring 10 on the Mohs scale of mineral hardness. Diamonds are formed deep within the Earth's mantle under high pressure and temperature. They are commonly used in jewelry and industrial applications such as cutting and grinding due to their extreme hardness.

Graphite:
Graphite is a form of carbon that occurs naturally as a mineral. It is composed of stacked layers of carbon atoms arranged in a hexagonal lattice structure. Graphite is very soft and has a low hardness value on the Mohs scale. It is commonly used in pencils and lubricants due to its slippery and low-friction properties. Unlike the other options, graphite is not considered a hard rock.

Therefore, the correct answer is option 'D' (Graphite).

Chalk as a Writing Tool
Chalk is a soft, white rock that is commonly used to write on blackboards. Here's why chalk is the correct answer for this question:

Composition:
- Chalk is primarily composed of calcium carbonate, which gives it its characteristic white color and soft texture.
- The softness of chalk makes it easy to write with on a blackboard, as it leaves a visible mark without damaging the surface.

Usage on Blackboards:
- Chalk has been used as a writing tool on blackboards for centuries due to its effectiveness and affordability.
- When writing with chalk on a blackboard, the calcium carbonate in the chalk leaves a white mark on the dark surface, making it highly visible.

Alternative Options:
- Graphite is a dark, metallic mineral used in pencils, not chalk.
- Talc is a soft mineral often used in cosmetics and baby powder, not chalk.
- Quartz is a hard mineral commonly used in jewelry and construction, not chalk.
In conclusion, chalk is the correct answer for a soft, white rock used to write on blackboards due to its composition, historical usage, and distinctive properties that make it suitable for this purpose.

Explanation:

Introduction:
Diamond is a precious gemstone that has been highly valued for its beauty and durability for centuries. It is one of the hardest naturally occurring substances found on Earth.

Properties of Diamond:
1. Transparency and Color: Diamond is transparent, meaning it allows light to pass through it. It is colorless, but it can also come in various colors such as yellow, blue, pink, etc., depending on impurities present in the crystal lattice. So, option (a) is correct.

2. Cutting Glass: Diamond is extremely hard and has a high refractive index, which means it can be used for cutting and shaping other materials. Due to its hardness, it can easily scratch and cut glass. This property makes diamond an ideal tool for industrial use, especially in cutting and grinding operations. So, option (b) is correct.

3. Use in Jewellery: Diamond is highly prized for its beauty and is extensively used in making jewellery. It is cut into various shapes and sizes, such as round, princess, oval, etc., and set in precious metals like gold or platinum to create stunning pieces of jewellery. Diamonds are often used as center stones in engagement rings, earrings, necklaces, and bracelets. So, option (c) is correct.

4. Hardness: Diamond is the hardest known natural material. It scores a perfect 10 on the Mohs scale of mineral hardness, which measures a mineral's resistance to scratching. This means that diamond is extremely durable and resistant to wear. It can only be scratched by another diamond. So, option (d) is incorrect. Diamond is not a soft rock but the hardest naturally occurring substance.

Conclusion:
In conclusion, diamond is a transparent gemstone that can cut glass and is extensively used in jewellery making. It is not a soft rock but the hardest natural material. Therefore, option (d) is not correct.

What happens to the pieces when rocks break up?

When rocks are broken up by water and wind, the smaller pieces that are produced are not simply discarded or destroyed. Instead, they go through a natural process that allows them to become an essential part of the environment. The correct answer to the question is option 'B' - they become part of the soil. Let's explore this in more detail.

1. Weathering and erosion:
- Water and wind are agents of weathering and erosion, meaning they have the ability to break down rocks into smaller pieces.
- Water enters the cracks and crevices of rocks, and when it freezes and expands, it exerts pressure that causes the rock to break apart.
- Wind can carry small particles such as sand, which can act as abrasives, wearing down rocks over time.

2. Formation of soil:
- The smaller pieces of rock that result from weathering and erosion are called sediment.
- Sediment can vary in size, from tiny particles like clay to larger fragments like sand and gravel.
- Over time, these sediments accumulate and mix with organic matter, such as dead plants and animals, to form soil.
- The process of soil formation is called pedogenesis.

3. Importance of soil:
- Soil is a vital resource for plants, animals, and humans.
- It provides a medium for plant growth, supplying nutrients, water, and anchorage for roots.
- Soil also serves as a habitat for a wide range of organisms, including earthworms, insects, microorganisms, and burrowing animals.
- It acts as a filter, purifying water as it percolates through the soil layers.

4. Nutrient cycling:
- As rocks break down and become part of the soil, they release minerals and nutrients that are essential for plant growth.
- This process, known as nutrient cycling, ensures that these vital elements are continuously recycled and available for use by living organisms.

Conclusion:
In summary, when rocks break up due to the forces of water and wind, the smaller pieces become part of the soil. This process is important for the formation of soil, which provides essential nutrients and support for plant growth, serves as a habitat for various organisms, and plays a crucial role in nutrient cycling.

Explanation:

Pebbles are a kind of rock:
- Pebbles are small, rounded rocks that are typically smooth and often found on beaches, riverbeds, or in other natural environments.
- They are formed through the natural process of erosion and weathering, which breaks down larger rocks into smaller pieces over time.
- Pebbles are composed of various minerals and can vary in color, size, and shape depending on their geological origin.

Pebbles are not a kind of mineral or soil:
- While pebbles are made up of minerals, they are not classified as a specific type of mineral themselves.
- Similarly, pebbles are not considered soil, as soil is a mixture of organic and inorganic materials that support plant life and is typically found on the Earth's surface.

Conclusion:
Pebbles are a type of rock that can be found in various natural environments, and they are formed through the process of erosion and weathering. They are not classified as a mineral or soil, but rather as small, rounded rocks composed of different minerals.