The correct answer is Igneous rocks.

Igneous rocks are formed through the cooling and solidification of molten rock (magma or lava). This process, known as crystallization, occurs at relatively high temperatures. Magma, found beneath the Earth's surface, cools slowly, leading to the formation of coarse-grained igneous rocks like granite. Lava, which erupts onto the Earth's surface, cools rapidly, resulting in fine-grained igneous rocks such as basalt. The high temperatures involved in the magma and lava formation and subsequent crystallization are key to the formation of these rocks. Metamorphic rocks form from the transformation of existing rocks under high pressure and temperature, not primarily through crystallization of molten material. Sedimentary rocks are formed from the accumulation and cementation of sediments, a process that does not involve high-temperature crystallization. Volcanic rocks are a specific type of extrusive igneous rock formed from the rapid cooling of lava, which is still a high-temperature crystallization process. Therefore, the formation of igneous rocks directly aligns with the question's description of high temperatures and solid crystallization.