62 Journal of the Mitchell Society [ November 
but the majority contain from 3 to 9 per cent of this oxide. It is 
the presence of the thorium oxide that gives the monazite its com- 
mercial value. The analysis occasionally shows also the presence 
of other constituents, as the yttrium and erbium oxides, zirconia, 
alumina, magnesia, lime, iron oxides, manganese oxide, and tita- 
nium ozide. 
Monazite is light yellow, honey yellow, reddish, brownish, or 
greenish yellow in color, with a resinous to vitreous luster, and is 
translucent to subtransparent. It is brittle with a conchoidal 
to uneven fracture, and is from 5 to 5.5 in hardness. It crys- 
tallizes in the monoclinic system, and some crystals have been 
observed that were 2 inches in length. The more perfect crystals 
are, however, very small, ranging from an eighth to a sixteenth 
of an inch in length down to microscopic ones. 
The mineral is usually readily recognized after a few samples 
have been examined. Its color, usually yellowish inclined to 
reddish, its hardness 5 to 5.5, being readily scratched by feldspar 
(hardness 6) or quartz (hardness 7), and its high specific gravity, 
4.64 to 5.3, are the chief microscopic properties that will aid in 
distinguishing it. The principal chemical and blow-pipe reactions 
that can be readily employed to identify monazite are the follow- 
ing: It is incompletely soluble in hydrochloric acid, but is com- 
pletely and readily acted upon by sulphuric acid. If oxalic acid 
is added to the very dilute filtered sulphuric acid solution, or to 
the solution obtained by fusing the mineral with soda, a precipi- 
tate is obtained which upon ignition becomes brick red, due to 
cerium oxide. Before the blowpipe the mineral turns gray, but is 
infusible. If heated with sulphuric acid, it colors the flame 
bluish green, due to phosphoric acid. 
The presence of the thoria content of the monazite, which is 
the substance for which the mineral is mined, varies quite widely 
from .01 to over 7 per cent. The following analyses of thoria 
will illustrate the variation in the percentage of this oxide. 
