A classmate states that igneous rock must always become a sedimentary rock next, according to the rock cycle. Explain why this is not correct.

Igneous gets spewed hot from the earth and solidifies as it cools.

Sedimentary is deposited cool from oceans and streams and hardens with age and pressure.

Your book must say something like that.
see:
http://geology.com/rocks/igneous-rocks.shtml
and
http://geology.about.com/cs/basics_roxmin/a/aa011804b.htm

The classmate's statement that igneous rock must always become a sedimentary rock next, according to the rock cycle, is not correct. The rock cycle is a model that describes the different processes through which rocks can change and transform into other types of rocks. While it is true that igneous rocks can sometimes be weathered and eroded to form sediments, these sediments do not always immediately go on to become sedimentary rocks.

To explain why this is not always the case, we need to first understand the different types of rocks in the rock cycle. The rock cycle consists of three main types of rocks: igneous, sedimentary, and metamorphic.

Igneous rocks are formed from the solidification of molten magma or lava. They can be classified as intrusive (formed inside the Earth's crust) or extrusive (formed on the Earth's surface). Examples of igneous rocks include granite, basalt, and obsidian.

Sedimentary rocks, on the other hand, are formed from the accumulation and lithification (compaction and cementation) of sediments. Sediments can be derived from the weathering and erosion of all types of rocks—igneous, sedimentary, and even metamorphic. Over time, these sediments can be deposited and undergo compaction and cementation to form sedimentary rocks such as sandstone, limestone, and shale.

Metamorphic rocks are formed when existing rocks, either igneous or sedimentary, undergo immense heat and pressure within the Earth's crust. These conditions cause the minerals within the rocks to recrystallize and form new minerals, resulting in the formation of metamorphic rocks like marble, slate, and gneiss.

Now, coming back to the classmate's statement, while it is possible for igneous rocks to erode and weather into sediments, what happens to these sediments next can vary. Sediments may become lithified and form sedimentary rocks, but they can also undergo other processes.

For example, sediments can be buried deep within the Earth's crust, subjecting them to significant heat and pressure, which can lead to the formation of metamorphic rocks. Alternatively, sediments may be exposed to melting temperatures, causing them to melt and form new igneous rocks. These processes clearly demonstrate that while sediments can indeed form sedimentary rocks, they can also transform into either metamorphic or igneous rocks, depending on the specific conditions they undergo.

In summary, the rock cycle is a continuous process of rock formation and transformation. While it is possible for some igneous rocks to become sedimentary rocks through weathering and erosion, it is not the only possible outcome. Sediments can also undergo metamorphism or recrystallization to form metamorphic rocks, or they can melt and solidify to form new igneous rocks. Therefore, it is not accurate to state that igneous rocks must always become sedimentary rocks next in the rock cycle.