17* TRAVELS IN BRAZIL. 



Bohniischen Mittelgebirges, p. 122. and 146,, in which the 

 red garnets ai'e found embedded. 



We have already mentioned the principal colours of the 

 topazes found in Brazil. Those in our possession, which 

 are for the most part crystallised, are, 1 st. four-sided prisms, 

 with cylindrical, convex, lateral planes ; and, 2dly. eight- 

 sided prisms, in which the lateral planes, meeting in a very 

 obtuse angle, may be clearly observed. In the first case 

 the prisms are acuminated by four planes, set on the lateral 

 planes ; in the latter, the solid angles of the nearly rect- 

 angular lateral edges are more or less truncated, so that 

 the acumination appears of six planes. The lateral planes 

 of the crystals are longitudinally striated, though, in 

 some of them this striation is hardly perceptible. The 

 terminating planes are rough, but some of them are so 

 evidently notched on the acuminating edges, which may 

 be considered as a continuation of the nearly rectangular 

 lateral edges, that it is impossible not to perceive the origin 

 of the ci-ystal out of many small ones, each of which had 

 a tendenc^r to form its own distinct acumination. In this 

 aggregation of several small crystals into one, we must 

 probably seek the cause of the striated lateral planes, and the 

 rough terminating planes. The remaining marks are com- 

 mon to them all, only in some dark yellow pieces, small 

 scales of ironglance, perhaps little six-sided tables, are em- 

 bedded, and seem thereby to allow the inference that the 

 topazes have a deeper colour in proportion as the surround- 

 ing lithomarge is more ferruginous. 



The euklase, which, in common with the emerald, occurs 

 in the modified mica, or scaly lithomarge (which contains 

 no magnesia, like chlorite and talc), is in the specimens of 

 a light mountain -green colour. The rarity of a complete 

 crystal will long be a hindrance to an accurate description 

 of it. The best defined crystal before us is a four-sided 

 oblique prism (according to the measurement of Mr^ 

 Fuchs, in Landshut,) of 115° and 65°, broken at one end. 



