216 Classification of Massive Rocks. 
D. &@ DIORITE PORPHYRITES. 
1, DIORITE PORPHYRITE contains plagioclase and hornblende as 
rphyritic constituents. 
2. MICA DIORITE PORPHYRITE contains plagioclase and biotite in 
porphyritic crystals. 
D. b QUARTZ DIORITE PORPHYRITES, 
1. QUARTZ DIORITE PORPHYRITE contains plagioclase, quartz and 
hornblende as the porphyritic ingredients. 
2. QUARTZ MICA DIORITE PORPHYRITE. In the rocks of this class 
biotite takes the place of the hornblende in the 
quartz diorite porphyrites. 
II. E. THE LAMPROPHYRE GROUP. 
The lamprophyre group differs from the granite porphyry 
group of vein rocks in that the iron and magnesium-bearing 
silicates, hornblende, pyroxene and biotite are the most important 
constituents occurring in two generations. Their feldspar, which 
may be either orthoclase or plagioclase, occurs in but one gener- 
ation. 
In composition they resemble the syenites and diorites of the 
intrusive rocks, and are therefore divided in accordance with this 
resemblance, 
A. SYENITIC LAMPROPHYRES, 
The syenitic lamprophyres consist of an alkaline feldspar, 
biotite, hornblende and pyroxene as essential constituents. 
They possess both the panidiomorphic-granular and the holo- 
crystalline-porphyritic structure. The former sometimes passes 
over into the hypidiomorphie-granular. | 
They are subdivided according to the presence or absence of 
biotite as a prominent constituent. 
1. MINETTEs contain biotite as the principal iron-bearing con- 
stituent, both in the granular and the porphyritie 
forms. 
(a) hornblende minettes contain hornblende in addition to 
i iotite. 
(B) augite minettes have augite besides biotite as a promi- 
nent constituent, 
