216 T. S. Hunt on the Constitution 
with a density of 3-5, 512-8 for the equivalent volume. Picros- 
mine, 2(Mg* Si?)4+-sHO corresponds to the formula sis sO«s(Mgz4 
H12)Ox«, differing from chrysolite by 12MO, and gives with a 
density of 2°68 a volume of 500-4. Serpentine, 2Mg, Sis, 3MgH, 
multiplied by three becomes sissOss(Mgz27His)Ois, which 
with a density of 2°55 gives 496-5 for the volume.  Villarsite, 
4M, Si+3H becomes sissOs«(Mg3sFe2MnH>)O.;, and with the 
assigned density of 2.975 gives a volume of 475°8. 
ses give the proportions of si to al, as 44:56, showing a partial 
replacement like that observed in some pyroxenes, and in the 
varieties of staurotide and kyanite, a consideration of whose vol- 
ume and equivalents we reserve for another occasion. 
The formula of iolite according to recent analyses by Scheerer, 
ite and fahlunite, represent these species as iolite plus water, and 
when compared with,that species are as follows: 
Chlorophyllite, : ° $iasOas(ta7RoHs )O. 2s 
Esmarkite, - A Sla sOas(ra 7RoH.)Os 5s 
Fahlunite, Sl4 sOas(re 7RoHis)Oss. 
probably belong to the same type with that species. From the 
e volumes and equivalents of the above species are as fol- 
ows :— 
* Pogg. Annal,, vol. xviii, p. 319, and this Journal, vol, v, p. 381. 
