For a rock to be considered an ore, it must:

For a rock to be considered an ore, it must:

• A. Be aesthetically pleasing
• B. Be formed by crystallization from magma
• C. Occur only in metamorphic terrains
• D. Contain enough of a commodity to be mined at a profit

Answer: (D)

The core idea is economic viability: a rock is considered an ore when it contains enough of a valuable mineral to justify extracting and processing it given current technology and prices. That means the rock must have a sufficient concentration, or ore grade, of the commodity to make mining profitable, which is why the correct answer is that it contains enough of a commodity to be mined at a profit. Aesthetics, or how the rock looks, doesn’t determine ore status; some valuable ores aren’t especially pretty. The way ores form isn’t limited to one process like crystallization from magma—many ores come from hydrothermal fluids, sedimentary processes, or other geological settings. And ores aren’t restricted to metamorphic terrains; they occur in igneous, sedimentary, and metamorphic rocks alike.

The core idea is economic viability: a rock is considered an ore when it contains enough of a valuable mineral to justify extracting and processing it given current technology and prices. That means the rock must have a sufficient concentration, or ore grade, of the commodity to make mining profitable, which is why the correct answer is that it contains enough of a commodity to be mined at a profit. Aesthetics, or how the rock looks, doesn’t determine ore status; some valuable ores aren’t especially pretty. The way ores form isn’t limited to one process like crystallization from magma—many ores come from hydrothermal fluids, sedimentary processes, or other geological settings. And ores aren’t restricted to metamorphic terrains; they occur in igneous, sedimentary, and metamorphic rocks alike.