Gemstone crystals should be very difficult to scratch. In 1812, a mineralogist named Friedrich Mohs developed a scale to rank the hardness of minerals. The diamond is at the top of the list. Not only is it the hardest gemstone, it is also the hardest substance known to humans! Rubies and sapphires are the next-hardest gemstones. Topaz, quartz, and emeralds are farther down on Mohs’ scale. The scale is useful in minerals.

Which word goes in the blank?

analyzing

mining

renewing

detecting