Chemical formulas of the Silicates. 255 
regards atomic weight; for Fe? is not Fe?, or two of the dyad 
Fe, as it seems on the face of it to be. The fiction is avoided in 
I. Unistnicates. 
A. Anhydrous. 
Forsterite, SiJO.]R, Si]O.] Mg. 
Fayalite, «“ Si]0,| Fe. 
Tephroite, SiJO,] Mn. 
Chrysolite, “ SifO.|(Mg, Fe). 
«“ Si]O,|(Fe, Mn)s 
Willemite, “ Si] 0,]Zn. 
Phenacite, “ Si] 0, | Be, 
t, Si]O0,](R, 8R)s SiJO.](FR+48R)2 
Meionite, - Si] 0.J(4R+38R)- 
Sarcolite, « SiJO.]GR+46R)2 
Allanite, “ SiJ0,](3R+48R): 
Epidote, « SiJO,]($R+#8R): 
Zoisite, age SifO.|(4R+26R)s 
~- Piedmontite, «“ SifO.](¢R+96R)s 
ite, « Si]O.1(gR+48R)2 
Tdocrase, «“ Si]O.]($R+23R)s 
Zircon, SiJO,]9R SifO.]yZr2 
Biotite, SiJO,1(@, BBR): —-S#Ou (4s, R)+48R)s 
Phlogopite A, “ SifO.I( (2, B)-+4,8R)s 
“ 8B . Si] 41(@(2, R)+48R)2 
Lepidomelane, A, “ \  SiJO.1(@(K., B)+48R)s 
aes t “ Sif 0,[(4(a, R)+48R). 
Astrophyllite,t  SiO,] (Rs, R.GR,7R)2  SilO.1(}4(@s, R)+BR+,7(Ti, 21))s 
— SiJO,|(R, BR, 58)2 SiJO.|(FR+48R+- 4582), 
* : bstitute these new formulas for those of the 
” The author does not propose to ering oe ons will sppeas only is 
Ae he ers “a Tapitomstin as analyzed by Schlotheim, with which belo 
“0 the Irish analyzed by ton. B is that of Rockport, Cape Ann, @ brittl 
ferriferous mica intermediate in ratio between Lepidomelane and the magnesia 
nt . 
From Pisani’s analysis, O. R., lvi, 846. 
