24 ANNALS NEW YORK ACADEMY OF SCIENCES 



cording to some) from magnesian limestone, of talc from steatite, etc., 

 confirms the advantage ot" sucli distinctive use of the two terms, if antigo- 

 rite as a definite mineral shall be held to comprise all substances of the 

 com{)Osition H4Mg3Si209. 



In most of its specimens, however careful their selection for apparent 

 purity, as judged by uniform texture, color and translucency, such as 

 ''noble serpentine,'' retinalite, etc., the evidences of large intermixture 

 with other substances are readily established. As this impurity mainly 

 consists of other magnesian salts, the usual method of identification of 

 antigorite by deduction of certain molecular ratios from the analysis is 

 by far too rude and unreliable. Only by recasting of the analysis/ with 

 precise reference to the percentage of combined water and, if possible, 

 with control by microscopic and optical examination of the very material 

 used for the analysis, can the true constitution be determined for the 

 aggregate present in almost every specimen of the presumably pure min- 

 eral. An unfortunate consequence of disregard of these precautions has 

 been the partial vitiation of many physical and chemical investigations 

 of the mineral. For example, it is easily determined, by recasting of the 

 stated analyses, that specimens of the "dark green sei-pentine" from 

 Newburyport, Massachusetts, selected as typical in experiments for de- 

 termination of constitutional formula,- actually contained 11 to 32 per 

 cent, of deweylite, etc. ; and that the foliated antigorite from Antigorio, 

 Piedmont, used for determination of the fonn of silicic hydrate existing 

 in the constitution of true antigorite,^ contained 15 per cent, of prochlo- 

 rite, deweylite, etc. It may be fairly suspected that this impurity of 

 material may have led in part to uncertainty attending conceptions of 

 that constitution. 



In regard to talc, its ordinary intermixture with quartz, chlorite, antig- 

 orite, tremolite, etc., is well known. 



2). The ohscunty of the products of decay in lajierite. — In past dis- 

 cussions, the grains of antigorite and scales of shining talc detected on 

 weathered outcrops, though merely ancient elements residual from their 

 insolubility, have been commonly mistaken for new generations. This 

 mislicading presumption has hindered recognition of the actual abundant 

 derivatives from rock decay, magnesia, its hydrate, carbonates and soluble 

 hydrosilicates. The resulting discordance of inferences from the numer- 

 ous proposed genetic hypotheses for talc and antigorite, with facts even 



lAnn. N. Y. Acad. Scl., XVIII, 129-146. 1908. 

 » Clarke and Sciinkider : Am. .Tour. Sci. (S). XL, .308. 1890. 



» S. IIillebrand: Sitz.-ber. d. math.-naturw. Kl. d. r. Acad. d. WIss., Berlin, CXV, 

 Abt. I, 697-712. 1906. 



