Question

Which type of rock forms because of high heat and pressure without melting? A. igneous rock C. sedimentary rock B. intrusive rock D. metamorphic rock

Short answer

The correct answer is D. Metamorphic rock.

Step-by-step solution

Understanding Types of Rocks

Begin by identifying the different types of rocks mentioned in the exercise. Igneous rocks form from the cooling and solidification of magma or lava. Sedimentary rocks form from the compaction and cementation of sediment. Intrusive rocks are a type of igneous rock that cools slowly beneath the Earth's surface. Metamorphic rocks form from existing rocks that are changed by heat, pressure, and chemical processes.

Matching the Description

The problem asks which rock forms due to high heat and pressure without melting. Igneous rocks require melting to form. Sedimentary rocks form from sediment, not heat and pressure. Intrusive rocks are igneous rocks. Only metamorphic rocks form from existing rocks undergoing change by high heat and pressure without melting.

Selecting the Correct Option

Since metamorphic rocks form due to high heat and pressure without melting the original rock, they match the given criteria. Thus, the correct option that describes a rock forming due to high heat and pressure without melting is D. Metamorphic rock.

Key concepts

Rock Formation

Rocks form in various ways, each associated with a specific process in nature. The Earth's geological processes give rise to three primary types of rocks: igneous, sedimentary, and metamorphic. Understanding these processes is essential to grasping how each rock type is created.
Igneous rocks originate from the solidification of molten material known as magma or lava. This can occur either beneath the Earth's surface or on it. When magma cools slowly below the Earth's crust, it forms intrusive rocks, which are a subgroup of igneous rocks. In contrast, when lava cools rapidly above the surface, it creates extrusive igneous rocks.
In contrast, sedimentary rocks develop from accumulated sediments. These sediments, which can include fragments of other rocks, minerals, and organic matter, are compacted and cemented over time. This type of rock often forms in layers, reflecting its origin from deposits of material in bodies of water, deserts, or glaciers.
Metamorphic rocks form through the transformation of existing rock types. This change occurs without melting, unlike igneous processes. Various conditions like high heat, enormous pressure, and sometimes chemical reactions cause the transformation, resulting in new mineral structures within the rock.

Heat and Pressure

The role of heat and pressure is crucial in forming metamorphic rocks. These two forces can induce profound changes in existing rocks, altering their physical and chemical states without melting them into a liquid form. This is the key transformation factor that sets metamorphic rock formation apart from the creation of igneous rocks.
Heat typically originates from the Earth's interior. It can increase due to the deep burial of rocks or proximity to molten magma. When rocks experience elevated temperatures, the minerals inside them can recrystallize into new formations.
Alongside heat, pressure is another transformative force. Pressure is usually the result of tectonic processes, such as continental collisions or the deep burial of rocks over time. It can cause the existing minerals to realign, exhibiting a finely banded or foliated appearance in some metamorphic rocks.
It is important to know that the conditions of heat and pressure do not reach a point where complete melting occurs. Instead, these sets of conditions reshape the rock at a solid-state level, enhancing or altering its texture and mineral composition.

Types of Rocks

Rocks can be classified into three main types: igneous, sedimentary, and metamorphic, each defined by the processes that form them. Each type showcases the dynamic nature of the Earth’s crust and the events it has undergone over millions of years.
Igneous rocks, such as basalt and granite, arise from solidified magma or lava. If formed beneath the Earth's surface, these rocks are termed intrusive, while those that cool on the surface are labeled extrusive. This cooling determines not just the rock's appearance but also its crystal structure.
Sedimentary rocks, including limestone and sandstone, form from sediment accumulation. Over time, layers of sediment are buried, compressed, and naturally cemented into rock, often right in water environments. They can contain fossils, providing insights into past life on Earth.
Metamorphic rocks result from the transformation of pre-existing rocks due to intense heat, pressure, or chemical activities. Common examples are marble, which originates from limestone, and schist, which is derived from shale. These rocks often display a foliated or banded texture, a testament to the pressures they underwent.

• Igneous: Formed from cooled magma or lava (granite, basalt)
• Sedimentary: Formed from compacted sediments (limestone, sandstone)
• Metamorphic: Formed under heat and pressure (marble, schist)