469 
FELSPAR. 
Genus IX. 
GENUS IX. SAP. 
SAP. 
Species I. 
Sp. 1. Felspar*. 
This stone forms the principal part of many of the 
Its Crystals. 
highest mountains. It is commonly crystallized. 
primitive form, according to De Lisle, is a rectangular 
prism, whose bases are rhombs, with angles of 65° and 
115°. Sometimes the edges of the prism are wanting, 
and faces in their place ; and sometimes this is the case 
also with the acute angles of the rhomb. For a de 
scription and figure of these, and other varieties, the 
reader is referred to Romé de Lidte t, Mr Hauyt, and 
Mr Pini§. 
Its texture is foliated: Its cross fracture, uneven. Properties. 
Fragments rhomboidal, and commonly smooth and po 
lished on four sides. Lustre of the polished faces often 
3. Transparency from 3 to 1. Hardness 9 to 10. Spe 
cific gravity from 2.437 to 2.7. Gives a peculiar odour 
when rubbed. It is made electric with great difficulty 
by friction. Fusible per se into a more or less trans 
parent glass. When crystallized, it decrepitates before 
the blow-pipe. 
Variety 1. Pure felspar. Moonstone—Adularia, 
Varieties. 
This is the purest felspar hitherto found. It occurs in 
Ceylon and Switzerland; and was first mentioned by 
Mr Sage. Lustre nearly 3. Transparency 2 to 3. 
Hardness 10. Specific gravity 2.559. Colour white; 
sometimes with a shade of yellow, green, or red. Its 
surface is sometimes iridescent. 
Variety 2. Common felspar. Lustre of the cross 
* Kirwan, i. 316. and Jour. de Pbys. passim. 
Crystall. ii. 461. 
t Mem. Par. 1784, p. 273. 
Sur de Nouvelle Crystallisation, &c. 8. 
G8 3