CLARKE. 
MICAS AND CHLORITES. 55 
with very little Si0 4 , and epichlorite is a mixture of this salt with the 
equivalent Al(Si0 4 ) 3 (MgOH) 6 H 3 , the two compounds being commingled 
in nearly equal percentages, or about half and half. 
Some of the chlorites, also, are parallel with kaolin and margaritein 
constitution. Aphrosiderite and strigovite, for example, are well 
represented, as follows: 
Kaolin. Strigovite. Aphrosiderite. 
.OH .OH .OH 
Al— Si0 4 ^EH 3 Al— Si0 4 =(FeOH) 2 H Al— Si0 4 =(FeOH) 3 
^Si0 4 =Al \si0 4 HAl X Si0 4 ^Al 
with much ferric 'iron in strigovite in place of aluminum. In diaban- 
tite we find a composition indicative of a mixture between a molecule 
of this type and one in the normal series. The diabantite from Cou- 
necticut, for instance, is very near 
.SiO=I(MgOH) 2 H .OH 
Al— Si0 4 =(MgOH) 2 H + 2A1— Si0 4 =FeH 
^SiO=(MgOH) 2 H \si0 4 ~FeH 
For the minerals daphnite, metachlorite, klementite, chamoisite, thur- 
ingite, and cronstedtite, the formulae are more or less doubtful, for the 
reason that alternatives are possible. They all, however, reduce to 
mixtures of the chloritoid or clintonite type, of the forms 
A. B. C. 
/O /O .O 
/ >R" / >R" / >R" 
Al— O Al— O Al— O 
\si0 4 =H.(A10H) X \Si0 4 =H 2 (R // OH) \si0 4 =H 3 
Using the letters underneath the formula as symbols, the several 
species become 
Chamoisite BA, with all R"=Fe 
Metachlorite BaC,, with all R"=Fe 
Thuringite AjBjC,, with all R'^Fe 
Klementite A^Ci, with R" mostly Mg 
Daphnite AiB 5 C 4 , with R" mostly Fe 
In cronstedtite there is a range from A^Ci, as in thuringite, to 
AiB 2 , and all the aluminum is replaced by ferric iron, while all R // = Fe. 
These expressions give the composition of the several species very 
closely, and serve to correlate them with delessite, rumpfite, prochlorite. 
and corundophilite. All of the valid evidence is satisfied, and the 
micas, clintonites, vermiculites, and chlorites form one systematic group. 
The facts that garnet and vesuvianite alter into chlorites, and that 
chloritic pseudomorphs after feldspar are known, serve to still more 
closely connect the formulae here adopted with the similar formulae of 
the preceding groups of minerals. 
