410 DESCRIPTIONS OF ROCKS. 
black pyroxene ; also the green hornblende or actinolite; the 
green foliated hornblende called smaragdite, and the foli- 
ated pyroxene sometimes wrongly called hypersthene, and 
another variety called diallage; ulso occasionally the species 
hypersthene and enstatite. 
5. The Feldspar-hke minerals, nephelite (p. 269) and leu- 
cite (p. 2471), which are related in constituents and quan- 
tivalent ratios to the feldspars, alumina being the only ses- 
quioxide base, and lime, potash, and soda the protoxide bases 
afforded in analyses; the atomic ratios for the protoxides, 
sesquioxide, and silica being in nepheiite, 1:3: 4, as in 
anorthite; and in leucite 1: 3:8, as in andesite. Also, less 
abundantly, Sodalite (p. 270), which has essentially the 
ratio of anorthite and nephelite. 
6. Minerals of the Saussurite group. These jade-like 
species differ from the feldspars—(1) in being always fine- 
erannlar in texture; (2) in having a hich densi Gs — 
2°9-3°4; in varying from the feldspar type chemically. 
They are near some soda-lime feldspars in constituents, but 
not always in the atomic relations of the constituents, nor 
in the absence uniformly of magnesia. There are two 
prominent kinds. One is between anorthite and zoisite in 
composition (see p. 263); yet, unlike these minerals, its 
analyses afford several per cent. of soda and some magnesia. 
The second approaches labradorite ; Delesse obtained for a 
specimen from Mt. Genévre (Alps), Silica 49°73, alumina 
29°65, iron protoxide 0°85, magnesia 0°56, lime 11:18, soda 
4°04, potash 024, water (with a little CO 3) On oes and a 
Silesian specimen afforded Vom Rath nearly the same result. 
A third kind from Corsica, according to Boulanger’s analy- 
sis, has nearly the same composition as zoisite. A fourth 
1s jadeite (p. 263), a stone occurring in the Swiss lake-dwell- 
ings—but not yet found in the saussurite rocks of Switzer- 
land. 
The saussurite of Siberia and the Alps has been observed 
to have sometimes the form of twins of a triclinic feldspar. 
This, and the texture, density, and composition, show that 
saussurite is, In part at least. pseudomorphous, and, in some 
revions, after labradorite. By some peculiar conditions in 
the process of metamorphism—perhaps long-continued ticat 
with an unusual amount of moisture—the ‘feldspar crystal- 
lizations that formed im the incipient stages of the process 
were afterward changed to a species of higher density and 
