SotLtas—On the Variolite and Associated Igneous Rocks. 109 
: “810 
Anorthite (sp. gr. 2°77), a7 300 (molecular volume), 
dis 884 
Zoisite (sp. gr. 3°38), saat 268. 
E 116 
Wollastonite (sp. gr. 2°8), Rar 41. 
SiicalG@ne er! 2:65) Seer 
ica (sp. gr. f AGE mt 
Thus the contraction which anorthite undergoes in passing 
into zoisite amounts to 10°6 per cent., and the result is similar if 
epidote be substituted for zoisite, while if the united volume of 
the anorthite and wollastonite molecules on one side of the equation 
be compared with that of zoisite and quartz on the other, the con- 
traction will be found to reach 14°3 per cent. Possibly the strong 
tendency to idiomorphic outlines displayed by epidote and zoisite 
is connected with this contraction in volume. The formation of 
chloritic minerals, on the other hand, is attended on the whole 
with expansion of volume. In investigating this complex group we 
may adopt T'schermak’s theory of their constitution, which in any 
case has the merit of conveniently expressing the facts. From this 
point of view the members of the chlorite family may be regarded 
as forming a series, having serpentine at one end, and a hypotheti- 
cal mineral, amesite, at the other, the intermediate members con- 
sisting of mixtures or combinations of these two simplest terms in 
various proportions, as shown in the following table :— 
Molecular Proportions. Simplest Formula. 
SPro, . . Si,0,Mg,H,, . : Serpentine. 
SpAt, - . SigQsALMgiHoo, } ee 
SpsAts, ; Si,0ic4],MgcH., } Clinochlore. 
Spat, . .  Si05Al,Mg,,H»,, 
Sp,At;, . : Sip309AL4M eg»; Huo, Prochlonice. 
Spe Ate, i : Si,O4; Al,M 1 Hy, i c Corundophilite. 
Atio, 5 ! Si0;AlMeoH,  . 4 Amesite. 
The constitution of amesite may be expressed by the formula:— 
Si] 0Al(OH),|(0.A10)(OMg0H)>. 
An actually existing mineral, with a composition closely approach- 
ing that of the hypothetical amesite, is a chlorite from Chester, 
1 Tf the specific gravity be taken as 2.75, the molecular volume will become 293. 
