THE 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



Art. YI. — On Wollastonite and Psuedo - Wollastonite, — 

 Polymorphic Forms of Calcium Metasilicate • by E. T. 

 Allen and "W". P. White, with optical study by Feed. 

 Eugene Weight. 



[By permission of the Director of the U. S. Geological Survey.]* 



Introductory. \ — Wollastonite is said to occur in massive 

 rocks as an original constituent, but is perhaps confined to 

 nephelme syenite such as is described from Alno by Torne- 

 bohm, who found it as inclusions in feldspar, in nepheline and 

 in segirine. Similar rocks have been described by Miigge and 

 others. It is also not uncommon in the crystalline schists. 

 In some such cases, like that described by Cross from Brit- 

 tany, the wollastonite is a secondary product and forms pseu- 

 domorphs after plagioclase. Among the crystalline limestones 

 of the ancient schist series it is abundant, and it is found also 

 in related rocks of the same series, such as garnetite and cal- 

 careous slates. Heinrich Wulf^: has also described it as an 

 original constituent of the crystalline schists in Hereroland in 

 Southwest Africa, and one of his rocks consists of nearly 

 equal parts, of wollastonite and diopside. 



Wollastonite is most abundant in and most characteristic of 

 contact metamorphic limestones, either along the periphery of 

 massives or in fragments included in a variety of eruptive rocks. 

 It is thus usually classed as a contact mineral. It often forms 

 well-shaped crystals of visible size, but no pseudo-wollastonite 



* This paper was prepared with the aid of a grant from the Carnegie Insti- 

 tution of Washington for this purpose. 



f For the introductory paragraphs upon the natural occurrence of wollas- 

 tonite, the authors are indebted to Dr. George F. Becker. 



% Min. Petr. Mitth., viii, 230, 1887. 



Am. Jour. Sci.— Fourth Series, Vol. XXI, No, 122. — February, 1906. 

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