76 THE CONSTITUTION OF THE SILICATES. [bull. 125. 
The original cyrtolite from Eockport is near malacone, but the cyrto- 
lite from Colorado, analyzed by Hillebrand, approximates to 
/OH 
„//OH 
Zr x 
\\Si0 4 =H(Zr0 2 H 2 ) 
\Si0 4 =H(Zr0 2 H 2 ) 
with part of the Zr0 2 H 2 replaced by other bases. These formulae, 
taken by themselves, are entitled to little consideration; but they 
become more significant when studied in connection with other com- 
pounds later. It will be noticed that one atom of zirconium is rep- 
resented as linking four groups or radicles together; just as one 
aluminum atom has a similar triple function in the aluminous ortho- 
silicates. This mode of linkage will be followed throughout this group 
of compounds. 
Iu eudialyte, elpidite, and catapleiite we have a group of zirconium 
silicates which form a highly suggestive series. Taking the simpler 
members first, they may be represented thus : 
Eljridite. Lime catapleiite. Soda catapleiite. 
OH /OH /OH 
/OH //OH //OH 
Zr x Zr X Zr { 
\ \Si 3 8 =^"aH 2 \ \OH \ \OH 
\Si 3 8 =NaH 2 \Si 3 O 8 =0aNa \Si 3 8 =Na3 
Connecting these formulae with zircon, we have the facts that Si 3 U 8 
occurs in auerbachite, and that at Laven, according to Brogger,* zircon 
is found both intergrown with catapleiite and pseudoinorphous after it. 
Eudialyte and eucolite are commonly regarded as metasilicates, with 
the compound ZrOCl 2 as an admixture. But the latter is not found in 
nature by itself, and both minerals, unlike most of the true metasili- 
cates, gelatinize with acids. Furthermore, the analyses of eudialyte 
and eucolite show a considerable range of variation in the ratio Si : O, 
although approximating somewhat nearly to the assumed Si0 3 . If 
now we treat eudialyte and eucolite as mixtures of tri- and orthosili- 
cates, like the feldspars, ssapolites, and some micas, all difficulties 
vanish, the chlorine becomes equivalent to hydroxyl, and the minerals 
fall into line with catapleiite and elpidite as the first members of the 
series. All varieties of eudialyte and eucolite are then interpretable 
as mixtures of the two molecules 
Zr< 
CI 
CI 
Zr ^Si 3 O 8 =0aNa 
\Si 3 8 =iCaNa 
Si0 4 =CaNa 
and 
Si0 4 ~CaNa 
Si0 4 =CaNa 
Si 3 8 =CaNa 
Zeitsch. Kryst. Min., XVI, p. 105. 
