Limestone isn't part of a rock group in the way you might think of a band. It's a sedimentary rock, meaning it's formed from the accumulation of sediments.

However, limestone can be part of a rock *sequence* or *formation*, which are groups of rocks that formed together in a particular geological setting. This sequence might include other sedimentary rocks like sandstone or shale, or even some metamorphic rocks.

Here's a breakdown:

* Limestone itself: It's a single rock type.

* Rock group: This term usually refers to a group of musicians.

* Rock sequence/formation: These are groups of rocks that occur together in a specific location.

So, while limestone doesn't belong to a "rock group" in the usual sense, it can be part of a larger geological sequence or formation.