Which of the following best defines an ore?

An ore is a naturally occurring solid material from which a metal or valuable mineral can be extracted profitably. The correct choice emphasizes this concept by stating that an ore is a rock that contains a metal worth extracting. This definition encompasses the key aspects of what makes a rock qualify as an ore: the presence of a metal and its overall economic viability for extraction.

In this context, the economic aspect is crucial. Mining and processing an ore involves costs, and thus the metal or mineral present must have sufficient value to justify these expenses. If a metal is valuable but too costly to extract, it does not meet the definition of an ore due to the lack of economic feasibility for extraction.

While other options refer to valuable minerals or costs, they don't fully integrate the necessary component of worthiness related to extraction, which is central to defining an ore in the context of economic geology.