Question

What sedimentary rock is made of large, angular pieces of sediments? A) conglomerate C) limestone B) breccia D) chalk

Short answer

The rock is breccia.

Step-by-step solution

Understand the Question

The question asks which sedimentary rock is made up of large, angular pieces of sediment. Sedimentary rocks are categorized by the size and shape of their sediments.

Identify Sedimentary Rock Types

We need to consider each rock type provided: conglomerate, limestone, breccia, and chalk. Conglomerate has rounded fragments, limestone is primarily formed from calcium carbonate, breccia consists of large, angular fragments, and chalk is formed from microscopic plankton.

Focus on Angular Sediments

Identify that the key term is 'angular'. Among the options, conglomerate features rounded clasts, whereas breccia features angular clasts.

Select the Right Rock Type

Since breccia is known for its composition of large, angular sediments, it matches the description given in the question.

Key concepts

Angular Sediments

When we talk about sediments being angular, we refer to their sharp, jagged edges. These pieces of material haven't traveled far from their source, so they haven't been subject to much natural wear. In contrast, sediments with rounded edges have typically been transported by forces such as water or wind over longer distances, smoothing out their roughness.
Characterizing sediments by their shape is crucial in geology. Identifying angular sediments helps us understand the conditions of their formation and deposition.

• Angular shape indicates limited transportation, offering clues about the environment where sediment deposition occurs.
• Angular sediments are typically found near the source rock due to minimal erosion.

Understanding angular sediments allows geologists to map ancient landscapes and reconstruct historical geological events.

Breccia

Breccia is a fascinating rock that is distinct because of its composition of large, angular fragments. Think of it as a collection of rock debris, cemented together over time.
The angular nature of the fragments in breccia shows that they haven't moved very far from their original location. The term 'angular' signifies the sharp, unrounded edges of the pieces which have been quickly deposited and compacted into rock form.
Breccia can form through various processes including:

• Volcanic activity, where fragments solidify in place after an eruption.
• Sedimentary processes, where materials collect in steep terrains or fault zones.
• Meteorite impacts, which rapidly break up rocks and redeposit them.

Each type of breccia shares its core characteristic: the presence of large, angular fragments.

Rock Composition

The composition of a rock tells us about its origins and the minerals it contains. For sedimentary rocks like breccia, composition is primarily defined by the fragments or clasts.
In the case of breccia, the clasts are the angular segments that define its texture. These clasts can be composed of various rock types, pointing to the varied sources they come from. Understanding rock composition involves:

• Identifying the mineral makeup of the clasts.
• Determining the source and transport history of these fragments.
• Analyzing the material that binds these fragments together.

The study of rock composition not only uncovers the story of breccia's formation but also its geologic history and the processes that led to its creation.

Sediment Size and Shape

Sediment size and shape are two critical factors in classifying sedimentary rocks. Size can range from fine silt to large boulders, and shape can be angular or rounded.
Sediment size is measured by diameter, and each size class has distinct characteristics and implications for the energy of the environment in which they were deposited.

• Smaller sediments usually suggest a calm environment, like a lake or deep ocean.
• Larger boulders indicate higher energy settings, such as fast-flowing rivers or landslides.

Shape determines how far the sediment has traveled. Angular sediments, as seen in breccia, indicate minimal travel and high-energy conditions close to their origin. Conversely, rounded sediments signify longer transport paths, where friction has smoothed their edges. Understanding sediment size and shape gives us a detailed picture of a sedimentary rock's journey from erosion to final deposition.