KINDS OF ROCKS, 444 
albite or oligoclase. Texture granitoid to fine-grained or 
compact. Color often grayish-white to greenish-white for 
the coarser kinds; olive-green to blackish-green for the 
finer. Very tough. G.=2-7-3:0. The quartz-bearing and 
quartz-less kinds-constitute two sections having similar va- 
rieties. Dark-red, brownish-red, and dark-green porphy 
ritic kinds, compact in base, have been called porphyryte. 
Metamorphic and eruptive. 
VARIETIES.—a. Granitoid ; granite-like in texture. b. Compact 
or fine-grained, with the feldspar grains scarcely distinguishable. 
c. Porphyritic ; the feldspar in crystals in a compact base. d. Slaty ; 
a dioryte slate or schist, usually chloritic. e. Micaceous. f. Apha- 
nitic (or Aphanite) ; nearly flint-like in texture. 
An analysis of a dioryte of the Hartz afforded Silica 5465, alumina 
15:72, iron sesquioxide 2-00, iron protoxide 6°26, manganese protoxide 
trace, magnesia 5°91, lime 7°83, potash 38°79, soda 2°90, water and ig- 
nition 1°96 =100°96. 
The antique red porphyry, or ‘‘rosso antico,” figured on page 415, 
- isan example of porphyritic dioryte. The crystals, according to the 
analysis of Delesse, are oligoclase, and have G.=2°67, while the base 
has G.=2-765, it consisting of an intimate mixture of oligociase and 
hornblende, with some grains of iron oxide. For the whole mass, accord- 
ing to Delesse, G.=2.763, but after fusion, only 2°486. Distinct acicu- 
lar crystals of hornblende occur in it. 'The rock is sometimes a brec- 
cia, being made up of angular fragments, either quite distinct from the 
mass or else shading off into it, but all alike porphyritic. The Mt. 
Dokhan, in which it occurs —‘‘ Porphyrites mons” of Ptolemy—con- 
tains also red syenyte similar to that of Syene, and a coarse red gran- 
_ ite. The ‘‘ porphyrite” of Ifeld, of Schénau in Bohemia, and the 
“¢ quartz-porphyrite ” of Koliwansk in the Altai are here referred. 
Propylyte and quartz-propylyte have the same constitution. The 
former is the prevailing igneous rock cf the Washoe district (vicinity 
of the Comstock lode), in Nevada; it is a grayish-green rock, yield- 
ing, on analysis, 64 to 66 per cent. of silica, and containing, along 
with oligoclase, hornblende, disseminated in minute points, and rarely 
also biotite (Zirkel). 
Ophite, of the Pyrenees, is greenish black dioryte. 
2. Andesyte. Quartz-Andesyte.—Contains the feldspar an- 
desite along with hornblende. As in the preceding, the 
hornblende is sometimes changed to chlorite. Quwartz-an- 
desyte, or Dacyte, is a quartz-bearing variety. Both kinds 
occur in the Washoe district. Eruptive. Also metamorphic? 
Banatite and Tonalite are like quartz-dioryte in most characters, 
but have the feldspar the species andesite. Each contains some bio- 
tite, the latter much of it. Banatite is from the Banat, and Tonalite 
from near Tonale, in the Southern Alps. 
Trachydoleryte (of Abich’, a dark gray to reddish-brown rock, some- 
what trachyte like in aspect, is, in part, near andesyte, it consisting of 
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