ALUMINA. 



325 



Colophonite — Silica 37.00, alumina 13.50, lime 29.00, oxide of iron 7. -50, oxide of 

 manganese 4.80, magnesia G.50, water 1 .00 [Simon). 



Allochroilc — Silica 35.00, ahiniiiia 8.00, liinc 30.00, oxide of iron 17.00, oxide of man- 

 ganese 3.50 ( Vauquelin). 



Pijrope — Silica 40.00, alumina 28.50, lime 3.50, oxide of iron 10.50, oxide of mano-a- 

 nese 0.3, magnesia 10.00, chromic acid 2. GO [Klaprolh). 



TopazuUte — Silica 37.00, alumina 2.00, lime 29.00, glucina 4.00, oxide of iron 25.00, 

 oxide of manganese 2.00 {Bonvoisin). 



Essonite or Cinnamon Stone — Silica 38.80, alumina 21.26, lime 31.25, oxide of iron 

 6.50 [Klaprofl'). 



Geological Situation. Garnet, in all its varieties, is most commonly found in primary 

 rocks. Those which, in this Slate, afford the best specimens, arc gneiss and mica slate, the 

 latter of which is often thickly studded with the dodecahedral crystals. It is sometimes found 

 in white limestone, but I am not aware that any of the varieties have been here observed in 

 the transition rocks. 



LOCALITIES. 



Dutchess County. Near the Foss ore bed in the town of Dover, crystallized garnet occurs 

 abundantly in mica slate. The colours arc red and dark brown, and sometimes the crystals are 



translucent. They are usually 

 small, very seldom exceeding 

 the size of a pea, and occasion- 

 ally associated with staurolite. 

 The forms are the primary 

 (Fig. 270) ; the primary with 

 the edges replaced by tangent 

 planes, emargine of Haiiy, Fig. 

 271, Pon worn' 150° 0', won 

 n or n' on ti 131 ' 48' 30", n on 

 n' 146'^ 26' 33'' ; the same with six of the sides extended, giving it the appearance of a six- 

 sided prism, and with two other sides assuming a hexagonal outline. Fig. 272 ; also Fig. 273, 

 in which six of the primary planes are extended, and all the edges are replaced bj- tangent 

 planes. 



At Stone church, in the same town, is another similar locality of garnet in a light coloured 

 mica-slate. The crystals arc in great abundance, and are similar in form to those observed 

 at the Foss ore bed. 



Essex County. In the town of Willsborough, nine miles northwest of the village of Essex, 

 there is a detached mountain mass, which extends from cast to west ; and on its northern face, 

 near the base, is a bed of the variety colophonite in gneiss. The bed is from two to five feet 

 in width, and the mineral is made up of largo grains of red, yellow ami deep lirovvn colours, 

 which have a high resinous hislre, and are frequently irised ; the single grains are liighly 

 translucent, and have a cleavage. Specific gravity 3.890. It is associated with the massive 



