clarke.] NORMAL ZEOLITES. 33 
scheme, as being from a chemical point of view more properly placed 
elsewhere. 
Three of the minerals in this group have already been mentioned, 
namely, hydronephelite, natrolite, and analcite. All of these occur as 
alteration products of elaeolite or nephelite,* and natrolite yields nephe- 
lite again upon fusion. Natrolite and analcite are both derivable by 
natural processes from albite;t analcite, as shown in the preceding- 
section, yields feldspathic pseudomorphs, and the relations of analcite 
to leucite are beyond controversy. From sodalite, both natrolite and 
hydronephelite may be generated, and from nephelite, by artificial 
means, Doelter has produced analcite and natrolite.! All of these rela- 
tions, with others, both morphological and genetic, are covered by the 
formulae which have already been developed, but which, in part at least, 
may be advantageously repeated here. Thus we have : 
Nephelite. Hydronephelite.* Natrolite. 
.Si0 4 E^a 3 .Si0 4 =Na 2 H .3i0 4 — JSaH 2 
Al— Si0 4 =Al Al— Si0 4 =Al. 3H 2 Al— Si0 4 =NaH a 
^SiO^Al ^SiO,— Al \si0 4 =Al 
Albite. Analcite. 
bi 3 u 8 =J>a 3 / >Al-Si0 4 ZE(A10H)H 
Al— Si 3 8 =Al Al— Si 3 8 =Na 2 3H 2 
\3ia0 8 =Al \si 3 O s -Al 
For the full significance of these expressions the previous sections 
must be consulted; the analcite formula being correlated with the 
formulas of garnet, leucite, and the minerals of the sodalite group. 
In a similar way, but rather less completely, many zeolitic minerals 
may be connected with anorthite, the calcium end of the plagioclase 
feldspar series. For example, by heating anorthite' Vith freshly pre- 
cipitated silica and carbonic acid water at 200°, Doelter obtained heu- 
landite.§ The same investigator, after fusion of various zeolites and 
subsequent slow cooling, found anorthite among the substances pro- 
duced by chabazite, heulandite, stilbite, scolecite, laumoutite, and 
thomsonite.|| In some cases anorthite was the chief product of fusion: 
in others it was subordinate to something else. Again, by various wet 
reactions, some of them unfortunately involving several stages, Lemberg 
has generated analcite 1] from chabazite, gmelinite, laumontite, harmo- 
tome, phillipsite, stilbite, and hi ulandite, in some cases studying several 
varieties of the same species. It is clear, therefore, that the connec- 
tion between the zeolites and the feldspars is unquestionable, and it 
* See Brogger, Zeit, Kryst. Min., XVI, p. 223 et seq. 
tNoues Jahrb., 1892, II, p. 1; Brauns. 
jNeues Jahrb., 1890, I, p. 134. 
§Neues Jahrb., 1890, I, p. 128, et seq. 
||Neues Jahrb., 1890, I, p. 118, and Allgem. Chem. Mineralogie, p. 183. 
UZeitseh. Geolog. Gesell., 1885, p. 959 et seq. 
Bull. 125 3 
