ORDER TII. PRISMATIC EMERALD. 313 



GENUS V. EMERALD. 

 1. PRISMATIC EMERALD. 



Prismatic Emerald or Euclase. JAM. Syst. Vol. I. p. 89. 

 Man. p. 190. Euclase. PHIL L. p. 101. Euklas. WERX. 

 Hoffm. H. B. I. S. 592. Euklas. HAUSM. II. S. 654. 

 Euklas. LEONH. S. 506. Euclase. HAU Y. Traite', T. II. 

 p. 531. Tabl. comp. p. 32. Traite', 2de Ed. T. II. p. 528. 

 WEISS. Verhand. der Gesellsch. nat. Freunde zu Ber- 

 lin. 1820. S. 110. 



Fundamental form. Scalene four-sided pyramid. 

 Vol. I. Fig. 41. 



Char, of Comb. Hemi-prismatic. 



Cleavage, highly perfect and very easily obtained 

 parallel to the faces T, Fig. 54., less distinct 

 parallel to P, which is a plane replacing the edge 

 7c, between d' and d, and parallel also to M 9 which 

 replaces the edge e between h' and h. Fracture 

 perfect conchoidal, and very easily obtained. 

 Surface, the faces between T and M streaked 

 parallel to their common intersection ; o some- 

 times curved, the rest of the faces very smooth 

 and shining. 



Lustre vitreous. Colour mountain-green, passing 

 into blue and white, always pale. Streak white. 

 Transparent ... semi-transparent, generally the 

 first. 



Very brittle and fragile, from which property the 

 name Euclase has been derived. Hardness = 7-5. 

 Sp. Gr. = 3-098, a greenish-white crystal. 



OBSERVATIONS. 



1. Prismatic Emerald, as yet a very rare mineral, has 



