38 GOLD AND TIN DEPOSITS OF SOUTHERN APPALACHIANS. 
that mine the pegmatite is very much like granite in appearance, and there the cassiterite 
is in small grains and less abundant than where the rock is coarser. Mica is not an abund- 
ant constituent, but is present locally, probably representing a transition to the fourth 
variety, which is in general characterized by much muscovite and little feldspar. A little ! 
hornblende has been found. On weathering this microcline pegmatite becomes very soft 
and clay-like, owing to the change of the feldspar into kaolin. 
The fourth variety of pegmatite is much more interesting mineralogically. While con- 
sisting generally of abundant quartz and large flakes of muscovite mica, with a small 
amount of orthoclase, microcline, and albite or oligoclase-albite, some of it varies decidedly 
from such a mineralogical composition. In places it contains little mica and much feldspar. 
The muscovite has been called a fluoric mica,a but an analysis by Mr. W. T. Schaller of] 
typical muscovite from the Jones mine gave only 0.15 per cent fluorine, which is rather 
below the average amount for muscovite. It is generally colorless, but yellowish or light- 
green colors are not unusual. Some of the flakes are several centimeters across. In some] 
of the dikes which contain other lithium minerals the muscovite is bordered by an extremely] 
narrow zone of lepidolite or lithia mica. In no other case has lepidolite been found. 
Spodumene, the lithium-aluminum silicate, is not uncommonly present, and in some dikes, 
particularly those rich in feldspar, constitutes a considerable proportion of the rock. It 
occurs in large and small individuals devoid of crystal outline but having well-developed 
cleavages intersecting at 93°. It is colorless to white and in some individuals has a silky - 
luster. Under the microscope the mineral is perfectly clear and colorless. The index of] 
refraction is rather high. The double refraction is probably not over 0.020. Extinction 
is inclined to the traces of cleavage in some sections and the maximum extinction angle 
observed was £ : e=24°. The mineral is biaxial and positive. Before the blowpipe itj 
fuses and gives a strong flame test for lithium. 
A yellowish-brown mineral occurring at the Faires mine contains lithium, manganese, 
phosphoric acid, and probably iron, and is undoubtedly lithiophilite. Where it has been 
subjected to decomposition near the surface — that is, to hydration and oxidation — it is] 
com cited into a black or brownish-black material of pitchy luster and conchoidal fracture,] 
which contains iron, manganese, phosphoric acid, and water, and is probably a definite 
mineral. In close association with the lithiophilite, occupying lenses and veinlets and in 
one specimen, occurring between the lithiophilite and its black oxirlation product, is a 
purple mineral which has been found to be a new species and has been named purpuritel 
The occurrence of this mineral indicates that if is a decomposition product of lithiophilite, 
and its chemical composition confirms this view. It is a hydrous manganic ferric phos- 
phate of the formula 2 [(Mil'", Fe"') P0 4 ] 1 I /), and is the only known case of a manganic 
phosphate. 
The mineral is probably orthorhombic, but crystal outline has in no case been observed. 
Two cleavages, presumabbj at right angles and pinacoidal, are of unequal perfection. The 
cleavage surfaces are in many grains somewhat curved, as if adjaeent particles of the mineral 
did not possess exactly the same orientation. It has an uneven fracture and is rather 
brittle. Its hardness is 4-4.5 and specific gravity about 3.15. In color the mineral is a] 
rich deep red or reddish purple, and the powder and streak have a decided purple or deep- 
rose color. 
Although purpurite is transparent in exceedingly thin pieces, giving beautiful red colors, 
the ordinary thin section of the mineral allows the passage of very little light. Parallel to 
the cleavage the color is a deep scarlet, inclining to rose-red, while across the cleavage the 
absorption is greater and the color becomes a rich purple. Extinction is generally parallel; 
an inclination up to 3° or 4° w r hich has been observed in a few instances has probably been 
due to the orientation of the sections examined. It may be, however, that the mineral is 
monoclinic, with a very small extinction angle. It was impossible to obtain an interference' 
a Pratt, J. H., and Sterrett, D. B., Bull. North Carolina Geol. Survey No. 19, 1904, p. 48. 
b Graton, L. C, and Schaller, W. T., Am. Jour. Sci., 4th ser., vol. 20, 1905, pp. 146-151. 
