£^ DESCRIPTION OF THE DICHROIT. 



reseent: 5, from the nepheline, or soramite, because 

 pieces of the latter immersed ii) nitric acid become cloudy 

 inievually, apd its speciiic gravity is less in the proportiou 

 of four to five; Q, from the hauyne, in the property of 

 the latter to resolve into a jelly in acids, 

 '^f^^ietici. There are four varieties. 1. The primitive dichroit, 



which is -4 re-rular hexaedral prism. 



^, The peridodecaedral. A reciangled prism, with twelve 

 fzices inclined to each other at angieg of l^^*. 



3. Amorphons. In large irregular grains, exhihiting 

 the rudiments of crystallization. 



4. Granular, In irregular musses, formed of very large 

 grains confusedly aggregated, 



^ranii'artncy. With respect to transparency, it is sometimes translucid, 

 somctitnes opake, 



^<?3our> All the crystals, or grains, viewed by reflected light, a,re 



of a violet colour, which is generally less bright in the Ion-* 

 g;itudinal direction of the prisms, 



^«,i))e Uy re- All the- translucid crystals or grains, seen by refracted 



^.aipii, light, are both of a brownish yellow and an indigo blue. 



When viewed parallel to the axis of the pris;m, they coii- 

 stautly exhibit a very deep blue : but when viewed perpen-» 

 diculiirly to. this axis, they are of a very light brownish 

 yellow. In the second case the transparency appear? to be; 

 increased in. the proportion gf six to one. 



>^1>!ef« fouTKj!. '^'^^^ dichroit is found in two places at Cape de Gattes; 

 namely, at Granatillo, near Nijar, where its situation wa§. 

 verilied anew last year by Mr, Tondi ; and at the foot of the 

 irwiuntains surrounding the bay of San Pedro, The pre* 

 ceding description is drawn up from specimens from the 

 latter place. They are found there in a vast horizontal 

 ledge of volcanic breccia. This breccia is composed of 

 detritus of every kind, but more particulaifly of fragnaents 

 and blocks of black or red scorice in perfect preservation, of 

 black vitreous lava, and of lithoid lava, either basaltic or 

 }^etro,sili(eous» The dichroit is found chiefly in blocks of 

 the latter kind. Sometimes it occurs in the form of scatter-* 

 ij.\ grains, sometiriies of crystals grouped, and an it were 

 imbeilded in the lava. It is found also not only in the gray 

 UJ,' whitifeh tufa,^ whieh serves as a base to the breccias bu^ 



ql8Q 



