Rock Cycle

Question

The rock cycle is the way that rocks on Earth change from one type of rock to another.

The three types of rocks are igneous, sedimentary, and metamorphic. Igneous rocks form when rock that has been melted to form liquid magma is cooled again. Sedimentary rocks form from small particles of rock that have been pressed tightly together. Metamorphic rocks form underground from heat and pressure. Processes that contribute to the rock cycle can occur quickly or take a very long time.

The model shows the rock cycle.

The rock cycle shows how energy from Earth contributes to metamorphic rock melting. The magma rises up through the volcano where it cools, creating igneous rock. The Sun's energy makes wind and water move. Wind and water cause weathering and erosion. Gravity causes landslides. These processes turn igneous rock into sediment, which settles in water. The sediment turns into sedimentary rock. Sedimentary rock undergoes heat and pressure, which turn it into metamorphic rock.

Constructed Response Question
A scientist finds a rock that is smooth and glassy. Identify the type of rock that the scientist most likely found and describe how it formed.

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Answer 1

The scientist most likely found an igneous rock, specifically a volcanic glass such as obsidian. This type of rock is characterized by its smooth and glassy appearance, which occurs when lava cools rapidly after being expelled from a volcano.

When magma from below the Earth's surface erupts during a volcanic event, it can flow out as lava. If this lava cools quickly, often due to exposure to air or water, it does not have enough time for crystalline structures to form. As a result, the lava solidifies into a glass-like texture, leading to the formation of rocks such as obsidian. Thus, the smooth and glassy characteristics of the rock indicate that it is an igneous rock formed through rapid cooling of molten material.