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The geology of volcanic islands is inherently dramatic and complex. When thinking specifically about their formation, it's essential to recognize that these landforms are born from the Earth’s mantle. Molten rock, known as magma, escapes through cracks in the Earth’s crust, reaching the surface and erupting as lava.

Upon eruption, lava cools and solidifies to form igneous rocks. Volcanic islands are therefore initially stacked layers of these solidified materials. Over time, the forces of erosion and sedimentation can add other rock types to the mix, like sedimentary rocks formed from the accumulation of debris and organic matter. However, volcanic islands can also host metamorphic rocks, which are not initially present but can form as a result of intense heat and pressure – conditions that can occur due to the geothermal activity of the volcano itself, or tectonic processes that might affect the island.

Igneous rocks represent a foundational chapter in the story of geology. They are the literal bedrock of volcanic islands and form directly from the cooling and solidification of magma or lava. This process can happen either beneath the surface—creating intrusive igneous rocks like granite—or above it, after a volcanic eruption, creating extrusive igneous rocks like basalt.

When molten rock cools quickly, the crystals that form are usually small because they don't have time to grow large; this is common with volcanic eruptions and results in rocks with a fine-grained texture. The initial rock types on a volcanic island, therefore, are usually fine-grained and dense, with basalt being the most common. These rocks can later undergo metamorphism, changing them into new forms of metamorphic rock.

The rock cycle is a fundamental concept in geology that describes the transformation of rocks through various geological processes. All three rock types—igneous, sedimentary, and metamorphic—are interconnected in this cycle, continuously being formed, destroyed, and formed again. Volcanic activity plays a critical role in this cycle, marking the beginning of many igneous rocks' journeys.

Over time, weathering, deposition, and sedimentation might convert these igneous rocks into sedimentary rocks. Then, with the right conditions, such as heat, pressure, and chemical activity—perhaps resulting from the volcanic activity itself or tectonic movements—both igneous and sedimentary rocks can become metamorphic. This means even on a volcanic island, the ongoing processes of the rock cycle can give rise to all rock types, showcasing the dynamic and ever-changing nature of the Earth's crust.