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GRAPHITE. 
The element carbon exists in three allotropic forms, one of 
which is the mineral graphite, also known as plumbago, and black 
lead. 
This mineral is soft, unctuous, and black or steel grey, has 
a metallic lustre, and is electro-conductive to a high degree. 
It is, practically, always associated with either igneous 
or metamorphic rocks, occurring in three manners. 
(1) Veins of crystalline (columnar, or foliated) graphite. 
(2) Lenticular masses of crystalline (flake), or amorphous 
graphite. 
(3) Particles of graphite, either crystalline (flake), or 
amorphous, disseminated through the country rock. 
The workable deposits, in nearly all cases, belong to the 
last of these classes. 
There are a number of minerals which are commonly as 
sociated with graphite, such as quartz, calcite, mica, chlorite, 
pyrite, and pyrrhotite, varying, of course, according to the 
rocks in which the graphite occurs. 
PREPARATION. 
Crude graphite of the third class, referred to above, and 
that containing impurities, must be subjected to a very elaborate 
milling treatment to prepare it for the market. 
It must be ground to such a degree of fineness as to detach 
the particles of graphite from the associated minerals. This 
grinding is not an easy matter, as the graphite cakes badly in 
the machines. Following the grinding, the graphite is separated 
from the accompanying minerals either by a wet or dry process 
of concentration. 1 The resulting concentrates are then graded 
into various sizes by screening and bolting. 
The graphite is further graded according to purity. 
1 For descriptions of various processes see: “ Graphite, its Properties, Occurrence, 
Refining and Uses,” by Fritz Cirkel. Report No. 18, Mines Branch.