J. B. Pearse on Minerals of the Chlorite Group. 225 
If I may be allowed to hazard a conjecture as to the introduc- 
tion of alumina to those simple minerals to build up the chlorite 
group, I suggest that it is due to the conjoined influence of adja- 
cent decomposed feldspar, and a solution of magnesia. For de- 
composed feldspar, I take the most general composition of kaolin, 
and for solution of magnesia, brucite. Grastite and kimmer- 
erite may: be supposed to be formed thus: 
Grastite : Sid, Al,0,; Mg,0 H,O 
1 atom of kaolin, 3 2 3 
2 * olivine, 2 4 
6." braeile; 5 5 
1 “© grastite, 5 2 9 8 
Kammererite: 
1 atom of kaolin, 3 2 3 
7 Onvine, 3 6 
1 “ serpentine, 2 4 2 
oS prucite, 5 5 
1 “  kammererite, 8 2 14. 10 
moment’s consideration will show that these conjectures are 
not unfounded. Chlorite is found where talcose matter and feld- 
adjacent feldspar, and serpentine has been supposed to de- 
rived from olivine. The locality in which grastite, rhodophyl- 
lite, and kiimmererite are remarkably developed, viz. Lancaster 
county, Penn., abounds in brucite. In fact brucite either as such 
Lancaster Co., 
enn. We have therefore only hazarded a natural conclusion, 
that chloritic minerals are formed from their simpler mineral 
associates, : 
Philadelphia, Oct. 26th, 1863. 
