110 Chester and Cairns — Crocidolite 



The mineral comes, then, under the general formula, R 6 RSi 9 27 , 

 where RO=FeO : Na„0 : H 2 : =3 : 1 : 2, and seems fairly en- 

 titled to take rank as one of the well authenticated mineral 

 species. 



Let us now compare the figures given above with the 

 published analyses of this mineral, which have all been made 

 on the crocidolite from South Africa, with the exception of 

 one by Delesse, to be considered later. 



Analyses. 



1* 2f 3J 



SiO_ 50-81 51-64 52-11 



Fe 2 3 • 20-62 



A1 2 3 .... 1-01 



FeO 33-88 34-38 16-75 



MgO 2-32 2-64 1-77 



CaO 0-02 0-05 



Na 2 7-03 7-11 [6-16] 



Mn"„0 3 .... 0-17 0-02 



H 2 5-58 4-1] 1-58 



In analyses 1 and 2 no attempt was made to determine the 

 ferrous oxide, and in 3 it it was' determined by the hydrofluoric 

 acid process in presence of carbon dioxide, a method that will 

 only give accurate results if care is taken not to raise the heat 

 too high. The total amount of iron found in each analysis 

 calculated to Fe 2 3 is as follows : 



l. 2. 3. 



Fe 2 O s 37-65 38-20 39-23 



while in the mineral from Rhode Island it is 4046 per cent. 



If now we correct these analyses to correspond with our 

 formula, calculating ferrous oxide in proportion to the silica 

 found in each case we shall have 



1. 2. 3. 



Si0 2 50-81 51-64 52-11 



Fe 2 3 18-60 19-46 18'49 



A1 2 3 1-01 



FeO 17-16 16-84 18-74 



MgO 2-32 2-64 1-77 



Na 2 ... 7-03 7-11 [6-16] 



H 2 588 4-11 1-58 



The ratios calculated from these revised figures are as 

 follows : 



* Stromeyer, fibrous var., Gott. gel. Anz., p. 1585, 1831. 

 ■J- Stromeyer, earthy var., Gott. gel. Anz., p. 1585, 1831. 

 | Dolter, Zeitschr. Kryst.. iv, 40, 1879. 



