CHAPTER VII. 
MINERALOGY— con^mwerf. 
Silicates (cowf(^. )—Epidotes, Micas, etc. 
Piedmontite — Ilvaite — Caipholite — Maugauese-micas — Manganchlorite? — Mangano- 
phyllite — Alurgite — Ottrelite. 
Piedmontite. 
The characters of this mineral as given by Dana are summarized 
below : — 
It belongs to the monoclinic system, crystalhzing in prismatic forms 
isomorphous with epidote, of which it is the man- 
Characters. . , 1 r r T • 
ganese variety. Also found massive. Cleavage 
c perfect; a less so. Fracture uneven. H.— 6-5. G. = 3*4 to 3'52. 
Lustre vitreous. Colour reddish brown and reddish black. Streak 
reddish. The most striking character of this mineral is its beautiful 
pleochroism as seen in thin sections under the microscope. The pleo- 
chroism scheme varies in specimens from different localities, but is 
generally — 
;l = yellow to orange. 
h = amethyst or violet to rose. 
c = rose to carmine. 
In composition the mineral is a basic orthosilicate conforming to the 
formula Ca2(A10H)(Al,Mn,Fe)2(Si04)3 or 
H20.4Ca0.3(Al,Fe,Mn)203.6Si02. The amount of manganese oxide, 
Mn203, in the pubUshed analyses varies from 4-52 to 15-00, corresponding 
to 3'5 to 10"5% of manganese. 
This mineral cannot be considered a common one ; it is found in the 
crystaUine schists of Japan, in the altered pre-Cambrian rhyohtes of 
Maryland and Pennsylvania in the United States of America, and in 
Piedmont, Brittany, and England. 
Ordinary epidote may be manganiferous, but this mangan-epidote 
^ is to be distinguished from true piedmontite by the 
angan epi o e. ^^^^ ^^^^ .^^ epidote, optically negative, 
whilst piedmontite is optically positive. Such mangan-epidote is found 
at Jakobsberg in Sweden, and it is the analysis of this mineral that 
gives the lower limit for Mn203 given above. 
