48 ELEMENTARY GEOLOGY 
it forms one of the other oxides, hematite (Fe,Os;) 
(Fig. 9). This is among the commonest of iron ores, 
being found in many parts of the world, in beds, as 
well as in the form of a red coloring-matter in the 
rocks. It also is heavy, and when it rusts forms the 
yellow mineral limonite (2 Fe,O,; 3 H,O). 
Fie. 9. 
Hematite. Botryoidal surface in lower part. 
An easy way of distinguishing the three oxides of iron, 
is by the streak, which is obtained by scratching the 
mineral upon a hard white substance, such as white 
quartz or rough porcelain. Limonite makes a yellow 
streak, hematite a red or brown mark, and magnetite 
a black streak. 
