Other Sources of Iron

It should be mentioned that iron is a minor constituent in an indefinite number of other minerals and rocks. Thus, it is present in small quantities in serpentine, biotite, hornblende, garnets, etc. Indeed, the mean percentages of ferrous and ferric oxides in British and American igneous rocks have been calculated to be as follow: -

	Fe2O3	FeO
British rocks	5.34	2.40
American rocks	2.65	3.35

so that the total amount of iron distributed throughout the igneous rocks of the world is very considerable.

Further, the brown and red colours of soil, clay, and sandstone are largely due to iron; sea, spring, and river waters contain dissolved iron compounds; and the metal also enters into the animal and vegetable organism, being an essential constituent of haemoglobin and chlorophyll. Spectroscopic examination of light from the sun and many fixed stars, reveals the presence of iron, thus showing that the metal is widely diffused throughout the universe.