SI 1. 1< ATKS. T1TA NATES, ETC. 



441 



p(1011), a (1120); Cleavage, prismatic and basal dis- 

 tinct; Brittle ; Fracture, subconchoidal ; H. = 5.5-6; G. = 2.55- 

 J.i M; Color, whittf, yellow, green, blue, brown, or red; Streak, 

 colorless or pale; Luster, vitreous to greasy; Transparent to 

 opaque; a) = 1.5416; c = 1.5376; a> - = .004; Optically (-). 



B.B. Fuses quietly at 3.5 (1100), yielding a yellow flame 

 (sodium). Gelatinizes with HC1 ; the solution freed of silica 

 yields .1 precipitate of aluminium hydroxide with ammonia. 



General description. Crystals when developed are short, 

 stout, hexagonal prisms terminated by the base or tabular parallel 

 to the base. Several pyramids of both the first and second orders 

 have been described on small crystals from the lavas of Monte 

 Somma, Vesuvius. 



Elaeolite is the more common granular or massive form of 

 nepheline, of the older syenites, in which it occurs at times as the 

 dominant mineral. 



Chemically nepheline is probably a mixture of sodium aluminium 

 orthosilicate (NaAlSiO 4 ), which has been produced artificially, 



FIG. 482. Nepheline in a Section of Phonolite. The Small Square Crystals are 

 also Nepheline. The Elongated Crystals are Feldspar. 



but is not known as a mineral, and potassium aluminium orthosili- 

 cate (KAlSiO 4 ), which is the mineral kaliophilite, with possibly a 

 little excess SiO 2 in its molecule. Eucryptite is the lithium salt 

 (I.iAlSi0 4 ), while cancrinite, HeNafiCatNaCOs^Alj^SiCMg, is a min- 



