How are the three main rock types formed?

How are the three main rock types formed?

• A. Igneous rocks formed by cooling magma or lava.
• B. Metamorphic rocks formed by existing rocks transformed by heat and pressure.
• C. Sedimentary rocks formed by weathering and cementation.
• D. Crystalline rocks formed by evaporation.

Answer: (B)

Heat and pressure inside Earth transform existing rocks into metamorphic rocks. The rocks don’t melt; instead the minerals recrystallize and rearrange under higher temperatures and strained conditions, which changes the rock’s texture and mineral makeup. This can produce foliated forms like slate and schist, where minerals align into layers, or non-foliated forms like marble or quartzite where crystals grow more randomly. The key idea is that metamorphism reshapes rocks without melting, driven by conditions such as deep burial or contact with surrounding magma and by tectonic forces squeezing rocks at convergent boundaries. This explanation fits the concept of one of the main rock types forming through the transformation of existing rocks by heat and pressure, distinct from igneous rocks that form by cooling molten material and sedimentary rocks that form from weathering, erosion, deposition, and cementation.

Heat and pressure inside Earth transform existing rocks into metamorphic rocks. The rocks don’t melt; instead the minerals recrystallize and rearrange under higher temperatures and strained conditions, which changes the rock’s texture and mineral makeup. This can produce foliated forms like slate and schist, where minerals align into layers, or non-foliated forms like marble or quartzite where crystals grow more randomly. The key idea is that metamorphism reshapes rocks without melting, driven by conditions such as deep burial or contact with surrounding magma and by tectonic forces squeezing rocks at convergent boundaries. This explanation fits the concept of one of the main rock types forming through the transformation of existing rocks by heat and pressure, distinct from igneous rocks that form by cooling molten material and sedimentary rocks that form from weathering, erosion, deposition, and cementation.