204 PHYSIOGRAPHY. 



Feldspar. 



granite which accompanies the Atlantic coast from Connecticut to 

 Maine, though often met with in the interior. Adularia, or opalescent 

 varieties, though not the most strongly marked, occur in Worcester co. 

 (Mass.) and in the granite bordering upon Lake George, near Ticonde- 

 roga, (N.Y.) as well as at Haddam, (Conn.) and Paris in Maine. Feld- 

 spar in very large, perfectly cleavahle individuals, and suited to all the 

 purposes of porcelain manufacture, abound in Charles co. (Penn.,) Dela- 

 ware, in the Highlands of New York, and at several places in N. Eng- 

 land, too numerous to be mentioned. Decomposed Feldspar is met 

 with occasionally in granite beds, as at Andover, (Mass.) ; in Cheshire, 

 (Conn.) a deposit was discovered in digging the Farmington Canal, 

 which appears to have owed its origin to the red sandstone formation. 



Several varieties of this species are used in the arts and manufactures. 

 The purest opalescent varieties of Adularia are cut round and polished, 

 and worn as ring stones, &c. The finest of them are from Ceylon, and 

 are called moon-stones. The sun-stone is also used in jewellery : it 

 exhibits, reddish and variegated patches of light, in the shape of ob- 

 lique-angled parallelograms on the cleavage face T. This variety is 

 found at Lyme, (Connecticut.) Graphic granite is cut for snuff- 

 boxes, &c. : it consists of a simple variety of the present species, reg- 

 ularly mixed with long parallel crystals of Quartz, whose transverse 

 angular sections bear some resemblance to certain letters. The pure 

 varieties of Feldspar are used in the composition of the paste of 

 porcelain, also for the enamel with which it is covered ; and the decom- 

 posed variety, or porcelain earth itself, is the most important material in 

 that department of manufactures. 



APPENDIX TO FELDSPAR. 

 i. Mikrodinous Felsite. BREITHAUPT. 



Pon M=~112 15'. PonT=902l/. M on T = 118 35', 



Cleavages very perfect. 



Hardness = 7-75 . . . 8-0. (scale of BREITHAUPT.) 



Sp. gr. = 2 562, reddish to liver-brown, from Arendal. 



2-565, reddish white, from Arendal. 



2 567, g*rey, with blue opalescence, from Friedrichs- 

 vairn. 



2-568, do. in small pure cleavage forms. 



