354 
DESCRIPTIVE MINERALOGY. 
EPIDOTE. 
[From the Greek erfidiSuiu, I increase; in allusion to the increase which the base of the primary under¬ 
goes in some of the secondary forms ( Thomson ).] 
Epidote. Hauy , Cleavdand, Phillips, Thomson and Shepard. — Prismatoidal Augitc. Jameson. — Prismatoidischer 
Augit-Spath. Mohs. — Zoizite and Thallite. Pendant. — Pistazit. Werner. 
Description. Colour green of different shades, occasionally 
almost black, rarely brown or reddish; also grey. Streak greyish 
white. It occurs regularly crystallized ; also granular and massive. 
Primary form a right oblique angled prism. Fig. 350. M on T 
114° 37 / (Hauy ); 115° 30' (Phillips). Cleavage perfect parallel 
to M ; less so parallel to P. Fracture conchoidal, uneven and splin¬ 
tery. Lustre vitreous, inclining to pearly and resino-pearly. Semi¬ 
transparent to translucent on the edges. Brittle. Hardness from 6.0 
to 7.0. Specific gravity from 3.42 to 3.44. Before the blowpipe, it intumesces, but does 
not, even by a strong heat, completely melt; with borax, it intumesces, and then fuses into a 
glass coloured by iron. It is not acted on by acids. 
Varieties. The name Epidote or Pistazite is applied to all the green coloured varieties. 
It is both granular and crystallized. 
Zoizite. This, which is sometimes described as a distinct species, has a grey, greyish yel¬ 
low or brown colour. It occurs crystallized and massive. The prisms are often much com¬ 
pressed, striated, and sometimes rounded. When massive, it is not unfrequently composed of 
broad fibres slightly diverging. It differs from epidote principally in its colour.* 
Manganesian Epidote. This occurs in small prismatic crystals of a violet or reddish brown 
colour. It contains about twelve per cent, of the oxide of manganese ; and before the blow¬ 
pipe, it fuses into a black glass ; with borax it exhibits the characteristic amethystine tint of 
manganese. 
Composition. Epidote (green) —Silica 37.00, alumina 27.00, lime 14.00, oxide of iron 
17.00, oxide of manganese 1.50 (Decotils). 
Zoizite (grey) —Silica 45.00, alumina 29.00, lime 21.00, oxide of iron 3.00 (Klaproth). 
Geological Situation. It is found almost exclusively in primary rocks, as gneiss, mica 
slate, sienite and white limestone. 
Fig. 350. 
LOCALITIES. 
Clinton County. Massive epidote is found in small quantities at the Arnold iron mine. 
* I have recently seen an article, probably written by R. Phillips, in which it is stated that the crystalline form of zoizite is the 
same as that of euclase, and has not a single face or cleavage in common with epidote. Pond. Edin. and Dub. Mag. &c. XX. 442. 
