53 
IRON OXIDES. 
As a rule, the minerals which consist essentially of iron 
oxides are looked upon as iron ores. In this report they will 
not be treated as such, but in the light of those uses which do 
not depend upon the extraction of their metallic values. 
Magnetite is a hard, black mineral of metallic lustre, com 
posed of ferrous-ferric oxide (FeO- FejOs, or FeaO^. It gets 
lts name from being strongly magnetic. 
Hematite 1 consists of ferric oxide, or sesquioxide of iron 
(FejOa). It varies in colour from bright red to black, though, 
when ground to a fine powder, it is always red. 
Limonite is the hydrated sesquioxide of iron (2 Fe 2 03 • 3 
^zO). is known also as brown hematite. Its colour varies 
from yellowish brown to black. 
Bog iron ore is a loose earthy variety of limonite occurring 
ln bogs. 
Ochre is the name applied to the earthy variety of limonite, 
Usually highly argillaceous. Its colour varies from brilliant 
yellow to dull yellowish brown. 
The presence of manganese oxides in ochre gives a brown or 
re ddish colour. This manganiferous ochre is called umber, 
nfter Umbria, in Italy, where it was first utilized. Sienna is 
*ke umber in composition, but contains less of the oxides of 
man ganese and is lighter in colour. 
USES. 
Paint '^ e uses °f these ferruginous materials are in the 
an( j ln dustry, where they are employed as pigments. Trueness 
v of colour are the prime requisites. They should be 
raw nC ^ ground, and free from grit. They are used either 
calcined, according to the colour desired, 
known C VCry finel y ground raw hematite produces the colours 
of the 1 ^ ^ nc ^ an rec f an( I Venetian red, but the principal source 
j se oolours is from the residue from pyrite burning. 
ing^tg 11 test ing all these materials for their suitability as pig- 
mi^’ a . carefull y dried and finely ground sample should be 
—_^_jwith oil and applied with a knife to a slip of clear glass. 
cial ly, as “ cammed limonite and the residue from pyrite roasting are known, commer- 
re d oxide.' 
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