Which type of sedimentary rock is considered a secondary rock type?

The concept of a secondary rock type relates to how rocks are formed and the processes they undergo. In geology, sedimentary rocks are divided into two main categories: primary and secondary. Primary sedimentary rocks are those that form directly from the accumulation and lithification of sediments. Secondary sedimentary rocks, on the other hand, are typically formed from the alteration or reworking of already existing rocks, which can include both metamorphic and sedimentary origins.

Metamorphic rocks, which is the correct answer, are formed when existing rocks—either igneous, sedimentary, or other metamorphic rocks—undergo transformation due to heat, pressure, and chemically active fluids. This transformation can lead to the creation of new minerals or structures within the rock, categorizing them as secondary because they exist as a result of the alteration of another rock type.

In contrast, igneous rocks form from the solidification of molten material (magma or lava) and do not fit into the category of sedimentary or secondary rocks. While sedimentary rocks can sometimes contribute to the formation of metamorphic rocks, they themselves do not represent a secondary type but rather are categorized as a primary rock type formed from sediments. Thus, the correct identification of metamorphic rocks as