MAGMATIC DIFFERENTIATION OF IGNEOUS ROCKS 641 
(bronzite), likewise quite iron-poor, and iron-poor hornblende, 
we may reckon a crystallization interval from about 1500° down 
to 1400° or somewhat lower. 
For hypersthene (with about 0.3FeSiO,-0.7 MgSiO,) the 
crystallization interval, according to the earlier approximate 
determinations, lies at about 1300—-1200°. 
In a silicate mixture, consisting of predominant labradorite 
(Ab,An,) and a little diallage and hypersthene, the labradorite 
Fic. 42.—From Romsaas (10:1) Fic. 43.—From Messel (8:1) 
Drawings of pyrrhctite-hypersthenite. In Figure 42 besides hypersthene there 
is a crystal of labradorite (with twinning lamellae), a little biotite, and traces of 
diallage. 
will commence crystallizing at about 1450°, and the essential 
part of the rock will be solidified at about 1300-1250° - The 
residual magma, present in quite small quantity, will crystallize 
along a eutectic boundary-line, down to about 1200° or probably a 
trifle lower. For the three pyrrhotite rocks just mentioned, the 
silicates must consequently in two cases have crystallized entirely 
and in the third case either entirely, or nearly entirely, while the 
sulphides were still in the liquid phase. 
At temperatures of 1500°, 1400°, and 1300° melted silicate of 
the composition of olivinite, hypersthenite, or labradorite-rich 
