* Rocks vs. Minerals: Rocks are made up of one or more minerals. Minerals are naturally occurring, solid substances with a definite chemical composition and crystal structure.

* Single Mineral Rocks: While some rocks are primarily composed of a single mineral, it's very rare to find a rock made up of *only* one mineral. Even rocks like limestone (mostly calcite) and quartzite (mostly quartz) often have trace amounts of other minerals.

The most likely "pair" of rocks that could be composed of a single mineral is:

* Limestone (Calcite)

* Quartzite (Quartz)

However, it's important to remember:

* Purity is rare: Finding a completely pure limestone or quartzite is uncommon.

* Other minerals are present: Even in these rocks, there might be tiny amounts of other minerals present.

So, the answer is that there is no perfect pair of rocks that can be *absolutely* guaranteed to be made of only one mineral.