174 



ALUMINA. 



ANDALUSITE. 



Trimetric. In right rhombic prisms. M : M=90 c 44' 

 Cleavage lateral, distinct; also massive and 

 indistinctly coarse columnar, but never fine 

 fibrous. 



Colors gray and flesh-red. Luster vitreous, 

 or inclining to pearly. Translucent to opaque. 

 Tough. H=7-5. Gr=31— 3-32. 

 Composition : silica 37-0, alumina 63'0. In- 

 fusible. With borax fuses with extreme difficulty. 



Varieties. Chiastolite and made are names given to 

 crystals of andalusite which show a tesselated or 

 cruciform structure when broken across and pol- 

 ished. The annexed figure represents one from 

 Lancaster, Mas«. The structure is owing to im- 

 purities, (usually the material of the gangue,) disseminated 

 by the powers of crystallization in a regular manner along 

 the sides, edges and diagonals of the crystal. Their hard- 

 ness is sometimes as low as 3. The same structure has 

 been observed by Dr. Jackson in staurotide crystals. 



Dif. Distinguished from pyroxene, scapolite, spodumene 

 and feldspar, by its infusibility, hardness and form. 

 Obs. Found in granite and gneiss. 



Westford, Mass. ; Litchfield and Washington, Ct. ; Ban- 

 gor, Me. ; Chester, Penn., are some of its American locali- 

 ties. Chiastolite occurs at Sterling and Lancaster, Mass., 

 and near Bellows Falls, Vermont. This species was first 

 found at Andalusia in Spain. 



STAUROTIDE. 



Trimetric. In right rhombic and six-sided prisms. M 

 M=129° 20'. Cleavage imperfect. 2 



P : a=124° 38', M : £nll5° 20. 



Figure 2 is a common cruciform 

 crystal, (consisting of two prisms 

 crossing one another.) Never in 

 massive forms or slender crvstalli- 



^ 



M 



zations. 



What is the appearance of andalusite ? Whr»t i? chiistclite or made * 

 How is andalusite distinguished from pyroxene and spodumene l What 

 crystalline forms are presented by staurotide ? Is it ever found massive I 



