366 Dr. A. Wilmore—Uralite and other Amphiboles. 
basic labradorite, pyroxene, green hornblende, and magnetite. AIL 
the forms and stages of uralitization may be seen, and it is possible to 
separate completely specimens of the almost unaltered pyroxene and 
the almost fully uralitized mineral. The results of the mean of two 
concordant analyses of these extreme cases are given. 
Pyroxene, D. 3358. Amphibole, D. 3°213. 
SiO, TEE Aas oP oe ON ee 43°34 
Al, O5 CRUSOE OBA te. LO eae 
Fee O3 £ : : —- 5 4 P 10°44 
FeO 6 ‘ a 10:07 : i F 7°92 
MnO . : : Traces , : 5 Traces 
CaO : 5 : 23°33 : ‘ 5 13°06 
Me 0 SUSAR ST AMMAR oct! 
K,0 Ogee zee i eRe 0-02 
15 0 BS reat a we cle ae 1:90 
Loss on heating . 5 — 0 . : 0:22 
100°25 102°10 
The authors claim that these analyses dispose of the idea of 
a dimorphous molecule, and that the remarkable freshness of the 
rocks preclude any idea of hydrochemical processes. The examina- 
tion of a great number of sections shows that the manner of the 
uralitization depends upon the permeability of the pyroxene. If 
the latter are impermeable the change is only peripheral; if, however, 
there exists in the pyroxenes ‘‘ une ligne de pénétration ou un 
accident quelconque dans la structure” the uralitization is internal. 
This is interpreted as showing that the pyroxenes after crystallization’ 
have been acted upon by the still liquid magma. The primordial 
magma has first of all allowed the crystallization of pyroxene and 
basic felspars. Before the complete consolidation of the rock the 
bath has been modified in composition by the action of mineralizing 
agents. The bath, thus modified, has reacted upon the pyroxenes, 
enriching them in alumina and in iron and depriving them of 
some lime. 
It appears probable that the explanation of Dupare & Hornung 
applies only to certain cases, otherwise one would expect uralitized 
pyroxenes to be as common in recent rocks as in more ancient igneous 
rocks, whereas it has over and over again been pointed out that 
uralitization is rarely found in the more recent basic rocks. The 
suggestion at once occurs that uralitization is a general term which 
has been used to describe more than one type of mineral alteration. 
These types may be tentatively summarized as follows :— 
(1) The alteration of diallage to uralite by the action of hot liquids under 
pressure and at high temperature and containing various dissolved salts, these 
liquids having penetrated the various planes of discontinuity in the crystals. In 
this way brown or green more or less compact hornblende may be produced 
according to the nature of the original pyroxene and the composition of the. 
penetrating fluid. 
(2) The alteration of compact secondary hornblende to fibrous actinolite or 
tremolite, by the gradual leaching out under conditions of moderately high 
pressure and temperature of more or less of the iron. This process seems to 
take place in the upper part of the zone of katamorphism, while the former 
process seems to be characteristic of the lower part of that zone. 
