Identify a substance that is NOT an allotrope of carbon.

Allotropy is the property of some chemical elements to exist in two or more different forms in the same physical state.
* Diamond, Graphite, and Buckminsterfullerene (${\text{C}}_{60}$) are well-known crystalline allotropes of carbon.
* Phosphorus is a completely distinct chemical element (Atomic Number $=15$, Symbol $=\text{P}$) belonging to the nitrogen family. It has its own allotropes, such as white, red, and black phosphorus, and is not an allotrope of carbon.