[Exacat]

Well, I don't know if, for example, graphite can be considered a compound or element.

Wikipedia defines compound as "a pure chemical substance consisting of two or more different chemical elements". If they have to be different elements, then it can't be a compound, right?

However, saying graphite or diamond is an element sounds uncertain.

What's the difference between pure neon gas and diamond when talking about if they are elements or compounds? Are allotropes considered as elements, compounds or simply allotropes?

[Arkcon]

However, saying graphite or diamond is an element sounds uncertain.

I don't understand this part here.  They are most definitely elemental forms of carbon.  They have very different physical and chemical properties, but that doesn't stop them from being elemental carbon.

[discodermolide]

The element carbon C agglomerates to a number of compounds of formula C_x. The latter being allotropes of the element, diamond graphite etc. Phosphorus and Sulphur do the same.
So allotropes are compounds in which the atoms are arranged in different ways.