What causes metamorphic rocks to form?

• A. Cooling of lava
• B. Accumulation of sediments
• C. Physical or chemical alteration from heat and pressure
• D. Weathering of existing rocks

Answer: (C)

Metamorphic rocks are formed through the process of metamorphism, which involves the physical and chemical alteration of existing rocks due to exposure to high temperatures and pressures over time. This process can occur deep within the Earth where tectonic activity causes rocks to experience intense conditions that change their mineral composition and structure, often resulting in the formation of new minerals that are stable under these conditions.

The key aspect of this process is that the original rock, whether igneous, sedimentary, or another metamorphic rock, undergoes transformation without melting. Instead, the solid-state changes allow for significant modifications in texture and mineralogy, leading to the unique characteristics of metamorphic rocks, such as foliation or banding.

In contrast, the cooling of lava pertains to igneous rock formation, while accumulation of sediments relates to sedimentary rocks. Weathering of existing rocks typically results in soil or sediment rather than the transformation into metamorphic rocks. Through understanding these distinct processes, it's clear why the transformation involving heat and pressure is the fundamental characteristic defining how metamorphic rocks are formed.