Which of the following is not classified as a rock?

A mineral is a naturally occurring inorganic substance with a definite chemical composition and a crystalline structure. While minerals are the building blocks of rocks, they themselves do not qualify as rocks. Rocks are classified into three main categories—igneous, sedimentary, and metamorphic—based on their formation processes. Igneous rocks form from the solidification of molten magma or lava, sedimentary rocks are formed through the accumulation and compaction of mineral and organic particles, and metamorphic rocks arise from the transformation of existing rocks under heat and pressure. In contrast, minerals are the individual elements or components that can combine in various ways to form different types of rocks.