Which of these is ALWAYS a property of an ore? A. It is renewable. B. It is black in color. C. It is cost-effective to extract. D. It is found in the earth's mantle.

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An ore is rock that contains valuable minerals in concentrations that can be economically extracted so C is the correct answer. Ores are mined from the earth, crushed and refined to produce minerals in a useable form.

The other choices are incorrect for the following reasons:

A. Ores aren't renewable. Metals and other minerals found in ores are limited in supply and aren't regenerated.

B. Ores aren't always black. They can be very colorful depending on the minerals they contain. The photo below shows some colorful minerals that are found in ores.

D. Ores aren't found in the earth's mantle, they're found in the crust. The crust is the outermost layer of the earth. It ranges from about 5 kilometers to 70 kilometers in depth. The mantle lies just beneath the crust, at a depth too great for practical mining operations.

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