130 ANNALS NEW YORK ACADEMY OF SCIENCES 



erals and may be regarded as established. On the other hand, albite has 

 not been found in any case to replace minerals other than those of the 

 primary consolidation of the magma. It is concluded, therefore, that it 

 appeared among the first results of alteration. At the same time quartz, 

 green amphibole, garnet, hematite and sulphide minerals (pyrite and 

 chalcopyrite) appear to have been produced. Where albite is found in 

 association with these, the contacts show no alteration on either hand. 



In the breaking-down of the original labradorite into albite and various 

 lime minerals, the presence of boric acid and other sublimates was un- 

 doubtedly a factor of great importance. Similar results of the action of 

 hot aqueous solutions upon igneous rocks, by which an original lime-soda 

 feldspar has disappeared and albite has been deposited in its place, are of 

 fairly common and widespread occurrence, and it appears that in general 

 the albite molecule possesses a much wider range of stability under condi- 

 tions which are apt to occur in nature than does the anorthite molecule. 

 While the more calcic feldspars normally occur as products of crystalliza- 

 tion from igneous fusion, albite is most frequently found under condi- 

 tions indicative of deposition from aqueous or aqueo-igneous solution at 

 much more moderate temperatures. Fouque^* observed that albite never 

 occurs individualized among the crystals of the volcanic rocks. Dana^^ 

 mentions instances of its formation under metamorphic conditions or as 

 a product of aqueo-igneous deposition as follows : 



It is found in disseminated crystals in granular limestone, thus in the lime- 

 stone (Jura and Trias) of the Col du Bonhomme, near Modane in Savoy; 

 also In microscopic crystals with quartz and orthoclase in limestone at Meylan 

 near Grenoble ; in minute crystals in fossil radiolarians in limestone near 

 Rovegno, Province of Pavia, Italy, also in the limestone itself; in limestone at 

 Bedous, Basses Pyrenees, at the contact with diabase. Some of the most 

 prominent European localities are in cavities and veins in the granite or gran- 

 itoid rocks of the Swiss and Austrian Alps, associated with adularia, smoky 

 quartz, chlorite, titanite, apatite and many rarer species. 



An instance of the passage of a lime-soda feldspar into albite is cited 

 by Dana^^ : 



INIiiuzing has investigated the Pfitschthal pericline and finds that the crys- 

 tals consist essentially of an oligoclase, rich in soda, upon which albite has 

 been deposited in parallel position, especially in the cavities of the original 

 crystals. 



W. C. Brogger,'^ in following out the paragenesis of the minerals of 



« C. HiXTZE : "Handbuch der Mineralogie," Leipzig, p. 1433, 1892. 



" "System of Mineralogy," 6th ed., p. 331. 



»/6id., p. 1026. 



«Zeltschr. fiir Kryst. und Mln., vol. 16, p. 167, 1890. 



