The rocks formed by gradual deposition, are called
🪨 Understanding Rock Formation by Deposition
The key term in this question is "deposition". Understanding this process is fundamental to classifying rocks.
Sediments: These are small, naturally occurring particles of rock, minerals, or organic matter that have been broken down by weathering and erosion.
Deposition: This is the geological process where sediments, soil, and rocks are added to a landform or land mass. Wind, ice, water, and gravity transport previously weathered surface material, which, losing energy, is deposited, building up in layers.
🔬 Detailed Analysis of the Options
A. Sedimentary Rocks
This is the correct answer. Sedimentary rocks are defined by their formation process, which is the gradual deposition of sediments. Over vast periods, these layers of sediment build up, and the pressure from the upper layers compacts the lower layers. Water carrying dissolved minerals then percolates through the spaces, cementing the particles together into solid rock in a process called lithification.
- Formation: Deposition, Compaction, and Cementation of sediments.
- Key Feature: Often found in distinct layers or strata. They are the only type of rock that can contain fossils.
- Examples: Sandstone, Limestone, Shale.
B. Igneous Rocks
This is incorrect. Igneous rocks are not formed by deposition. They are formed from the cooling and solidification of molten rock (magma or lava). The process is about temperature change, not the settling of particles.
C. Metamorphic Rocks
This is incorrect. Metamorphic rocks are formed when existing igneous or sedimentary rocks are transformed by intense heat and pressure. The process is about changing a rock's form (metamorphosis), not depositing new material.
D. None of these
This is incorrect as the definition perfectly describes sedimentary rocks.
➡️ The Journey of a Sedimentary Rock
The formation of sedimentary rock is a clear, step-by-step process:
- Weathering & Erosion: An existing rock on the Earth's surface is broken down into smaller pieces (sediments) by wind, rain, or ice.
- Transportation: These sediments are carried away from their source by rivers, wind, or glaciers.
- Deposition: As the transporting force (like a river) slows down, it loses energy and drops the sediments. They settle in a new location, often a lakebed or ocean floor, forming a layer.
- Compaction & Cementation (Lithification): Over millions of years, more layers are deposited on top. The weight compacts the lower layers, squeezing out water. Minerals dissolved in the remaining water crystallize, gluing the sediments together to form solid rock.
💡 Study Tips
- Deposition -> Deposit: Think of making a "deposit" at a bank. You are adding something. In geology, deposition is the process of adding layers of sediment.
- "Sedimentary" has "Sediment" in it: The name of the rock tells you exactly what it's made from.
- Picture a Layer Cake: Sedimentary rocks are the layer cakes of geology. Each layer was deposited at a different time.