[stopkillingme21]

Using my graph of an unknown sample in g/mL, I came up with 2 numbers of 2.25 g/mL and 2.27 g/mL. Those fit most closely to PTFE (2.20 g/mL) and Silicon (2.32 g/mL).

Which would you say my unknown most likely is: PTFE or Silicon?

[Vidya]

Information is not sufficient enough to give a clear picture.Can explain how you collected the data for the graph ?Then you need to see if the method adopted is more for positive error or negative error ...may be this will help us to predict which should be select. 

[Enthalpy]

So many compounds exist that a density cannot suffice to determine one.

But some more information would help you. For instance the colour differs between Ptfe and silicon (but doesn't suffice neither to determine a substance!). The odour too if feasible. Mechanical properties, and so on.

But possibly the first question is: what kind of substance did you expect? If it results from a reaction you made, you can narrow down the reasonably expected compounds.