Albertus Magnus's description of the ruby is a good example of how he combined firsthand knowledge with information he gleaned from his reading.

Carbuncle, which is anthrax in Greek, is called rubinus (ruby) by some, is a stone that is extremely clear, red, and hard. It is to other stones as gold is to other metals. It is said to have more powers than all other stones. But its special effect is to disperse poison in air or vapor. When it is really good it shines in the dark like a live coal, and I myself have seen such a one. But when it is less good, though genuine, it shines in the dark if clear limpid water is poured over it if in a clean, polished black vessel. One that does not shine in the dark is not...