97 
ture. ... In general these iron silicates are plainly still less 
homogenous, and on this account still more variable in composi- 
tion than the aluminium silicates.” 
Further, he quotes Knop as holding that some of these sup- 
posed iron silicates are only mixtures of iron hydrate with quartz 
or opal. 
Dana on the other hand,f without being able to ascribe to 
hisingerite a definite formula, accords it full specific rank, as also 
does Lacroix. § This attitude is amply justified by the closely 
concordant ratios existing between Fe,G :; , Si0 2 , 1LO+ and H.,0 — 
in specimens from widely separated localities. 
L. Woinschenk many years ago suggested || that nontronite is 
the homologue of kaolinite, its true formula being 
Fe.X ), • 2 S i (V 2 II, 0. 
Chloropal is then a mixture of nontronite with more or less opal. 
Reviewing the analyses and chemical and physical properties 
of hisingerite it appears to the author that this mineral is a dis- 
tinct species, the homologue of hatloysite. Its formula then is — 
Fe/F2Si0 2 ‘2II,0 + 2H‘o, 
with which further absorbed water is associated at times, e.g., in 
the Weston i a mineral. This formula requires 
45*4 per cent. 
SiO 34-9 
ao+ io*2 ” 
H 2 0- 10.2 „ 
t Loc. cit. 
§ Miner, de la France I., p. 405. 
II Zeit. Kryst. 28, 150 (1897). 
