Needs a discussion of why it hasn't held empirically 
Hotelling's rule makes a lot of intuitive sense, but it generally hasn't held empirically. The article needs to 1) state this fact, and 2) explain the various theories about why it hasn't held. For instance the price of iron ore has consistently declined over time in inflation-adjusted terms. The typical explanation for this phenomenon is around the decrease in extraction costs over time. If there have been a number of large new deposit discoveries, that would obviously also drive down the price.

I would add this info to the article myself, but I don't feel like I understand it well enough to add an incisive and accurate explanation.