172 ALUMINA. 



Damourite. Occurs in lamellar pearly crystals, a little harder than 

 talc. Gr=27 — 2*82. It is a hydrous silicate of alumina and potash. 

 Reported from Leiperville, Penn., and Chesterfield, Mass. It may be 

 only a hydrous mica. 



Chloritoid. A coarsely foliated mineral, folia bent, brittle ; color 

 greenish-black. H=5*5 — Gr=3 # 55. Infusible before the blowpipe, 

 but becomes finally black and magnetic. From the Ural. Sismondine 

 is a related mineral from St. Marcal. 



Masotiile is chloritoid. Occurs coarsely foliated or tabular; colot 

 dark gray; luster nearly pearly; folia brittle and often curved. H=6. 

 Gr=3 # 45. Fuses with difficulty on the edges. From the vicinity of 

 Natic village, Rhode Island. 



4. Anhydrous combinations with Silica. 



SILLIMANITE. 



In long, slender rhombic prisms, often much flattened, 

 penetrating the gangue. M : M=110° — 98°. A brilliant, 

 and easy cleavage, parallel to the longer diagonal. Also in 

 masses, consisting of aggregated crystals or fibers. 



Color hair-brown or grayish-brown. Luster vitreous, in- 

 clining to pearly. Translucent crystals break easily. H= 

 6—7-5. Gr=3-2— 3-3. 



Composition : silica 37*0, alumina 63'0. Identical there- 

 fore with kyanite. Infusible alone and with borax. 



Dif. Distinguished from tremolite and the varieties gen- 

 erally of hornblende by its brilliant diagonal cleavage, and 

 its infusibility ; from kyanite by its brilliant cleavage, and a 

 rhombic, instead of flat-bladed crystallization. 



Obs. Found in gneiss at Qhister, Ct., and the Falls of 

 the Yantic, near Norwich, Ct. The long, slender prisms 

 penetrate the gangue in every direction. Also in Yorktown, 

 Westchester county, N. Y. ^ ^^*W^. Co*a*»~- 



This species was named by Bowen in honor of Prof. B. 

 Silliman, of Yale College. 



Bucholzite is supposed to be a variety of Sillimanite. Composition, 

 silica 464, alumina 52*9, (Thomson.) A specimen from Chester, 

 Penn , gave Erdmann, silica 4(H, alumina 58'9, protoxyd of manga- 

 nese. From Fasea, Tyrol ; also from Chester, Penn. ; Munroe, Orange 

 county, N. Y. ; Worcester, Mass. ; and Humphreysville, Conn. 



What is the crystallization and appearance of Sillimanite ? What 

 w ito hardness ? How is it distinguished from tremolite and kyanite ? 



