In the early 19th century, who began classifying minerals by their physical characteristics and not, as had been done traditionally, by their chemical composition?
Friedrich Mohs Theophrastus and Pliny the Elder had compared the relative hardness of minerals, which was the basis of the "hardness scale" developed by Mohs.
What animal, introduced to Australia in the 19th century, had a feral population there by 2010 of between 500,000 and 750,000?
