PHYSIOGRAPHY. 



Plumbago Plumbocalcite. 



4. One of the most remarkable deposits of Plumbago is at Borrowdale 

 in Cumberland, in a bed of trap, very much interrupted, and alternating 

 with clay-slate. It occurs crystallized in Greenland, in the parish of 

 Pargas in Finland ; and different varieties are known from the Tyrol, 

 Salzburg, Piedmont, France, Spain, and Norway. 



Plumbago is of very common occurrence in the United States. Some 

 of the handsomest crystallized varieties occur near Ticonderoga on Lake 

 George, upon Roger's rock, where it is associated with Pyroxene and 

 Sphene ; and in the vicinity of Amity, Orange county, (N.Y.) at which 

 place it occurs in white limestone, with Spinel, Brucite, Hornblende, 

 &c. A compact variety is found in large masses, disseminated in veins 

 through gneiss, at Sturbridge, (Mass ) A similar variety occurs atGren- 

 ville, (Lower Canada,) along with Sphene and Tabular Spar, in white 

 limestone. 



5. Plumbago is much employed in the manufacture of lead pencils, 

 and of crucibles. It is also used to diminish friction, and to protect iron 

 from oxidation. 



PLUMBOCALCITE. Microtine Lime-Haloide. 



Primary form. Rhomboid. P on P = 104 53' 30". 



Surface of the crystals rounded. 



Lustre pearly. Color white. Transparent to translu- 

 cent. 



Hardness =2-5 . . . 3-0. Sp. gr. =2-82. 



Compound Varieties. Massive. 



1. Heated in a platina crucible, or in a glass tube, it decrepitates, and 

 after some time assumes a brownish, or pale reddish, tint. A small frag- 

 ment, dissolved in muriatic or nitric acid, gives a white precepitate, with 

 caustic ammonia, which becomes black on the addition of hydrosulphu- 

 ret of ammonia. 



2. Analysis. 



By TURJVER. 



Carbonate of lime ...... 92-2 



Carbonate of lead . ..... 7.3 



3. It occurs at Wanlockhead in Scotland. 



