170 ALUMINA. 



of gmelinite, but appears to drfferin containing just one third 

 the proportion of water ; also phacolite, occurring in small 

 glassy crystals having the form of double six-sided pyramids. 

 The acadiolite is a red variety from Nova Scotia. Herscheh 

 ite is another variety in small hexagonal tables. 



The varieties intumesce and whiten before the blowpipe 

 Gmelinite forms a jelly with acids. 



Dif. The nearly cubical form often presented by the crystals 

 of chabazite is a striking character. It is distinguished from 

 analcime as stated under that species ; from calc spar by its 

 hardness and action with acids ; from fluor spar by its form 

 and cleavage, and its showing no phosphorescence. 



Obs. Found in trap, gneiss, and syenite. Chabazite is 

 met with in the trap of the Connecticut valley, but in poor 

 specimens ; also at Ha^lyme^ and Stonington, Ct., at Charles- 

 town, Mass., Bergen Hill, N. J., Piermont, N. Y. Nova 

 Scotia affords common chabazite and also the ledererite. The 

 Faroe Islands, Iceland, and Giant's Causeway are some of 

 the foreign localities. Gmelinite comes from the Vicentine ; 

 also the county of Antrim, Ireland ; levyne from Glenarm 

 Scotland ; also Iceland, Faroe, &c. 



Haydenite. Resembles chabazite in the appearance of ite crystals 

 and is probably the same species. Occurs with heulandite at Jones's 

 Falls, near Baltimore. 



PREHNITE. 



Primary form aright rhombic prism; M : M = 99° 56. 

 > Cleavage, basal. Usually in six-sided prisms, round- 

 ed so as to be barrel-shaped, and composed of a 

 series of united plates ; also in thin rhombic or 

 hexagonal plates. Often reniform and botryoidal ; 

 texture compact. 



Color light green to colorless. Luster vitreous, 

 except the face P, which is somewhat pearly. Subtranspa- 

 rent to translucent. H=6 — 6*5. Gr = 2*8 — 2*96. 



Composition : silica 43*0, alumina 23*25, lime 26*0, pro- 

 toxyds of iron and manganese 2*25, water 4*0. On char- 

 coal before the blowpipe froths and melts to a slag of a light 

 green color. Dissolves slowly in muriatic acid without ge- 

 latinizing, leaving a flaky residue. 



How is chabazite distinguished from calc spar 1 ? how from fluorspar 

 What is the usual form and structure of prehnite? What is its 

 color? luster? hardness? 



