54 THE CONSTITUTION OF THE SILICATES. [bull. 125. 
while in prochlorite and corundopliilite the latter compound predom- 
inates. Prochlorite has the last formula, with trifling admixtures of 
chloritoid or ottrelite, and corundophilite agrees with the composition 
/°>Mg /°>Mg 
7A1-0 + 33A1-0 
\si0 4 =(AlH 2 2 ) 2 H ^SiO t :Z(MgOH)H 2 
In both prochlorite and corundophilite there are large replacements of 
magnesium by iron. 
To these formula? some of the rarer or obscurer chlorites offer inter- 
esting variations, which, however, are all simple and intelligible. 
Thus, rumpfite is represented by the formula 
/°>Mg /> H 
3A1-0 + 2 Al-OH 
\si0 4 =H(AlOH) \siO=H 3 
the first compound being a magnesian chloritoid, and the second a 
molecule already indicated in cookeite. The original delessite is very 
near 
/°>R" 
Al-O 
\si0 4 =H 3 
while the Scotch delessites, analyzed by Heddle, agree sharply with 
the formula 
.SiO=(MgOH) 2 H 
Al-SiO =(MgOH) 2 H + 2H 2 
\siO=Al 
with one-fourth of the Mg replaced by Fe. In the last case the dis- 
crimination between hydroxyl and water of crystallization is shown by 
the analyses, and it is very probable that an analytical revision of the 
chlorites would bring other instances of the same kind to light. 
For melanolite we have very closely the composition 
.Si0 4 =(Fe // OH)H 2 
Fe— Si0 4 =(Fe"OH)H 2 
\si0 4 =Fe 
and for euralite 
.Si0 4 =(MgOH) 2 H .Si0 4 =(MgOH)H 2 
7A1— Si0 4 =(MgOH) 2 H + 3A1— Si0 4 =(MgOH)H 2 
\Si0 4 =Al \Si0 4 EE(MgOH)H 2 
Trisilicate molecules, as among the micas, also appear in the chlorite 
series, and stilpnomelane is a good example of this kind. Its formula 
is very nearly 
/ Si 3 8 EE(FeOH) 2 H 
Al— Si 3 8 =(FeOH) 2 H 
\si 3 8 =(FeOH) 2 H 
