some Silicates of Alumina. 



361 



99-455 

 The formula, to represent its composition, which I am 

 disposed to adopt, is 



2 Al S + Al S« + 2 Aq. 

 According to Berthier's view it would be, 



2 Al S^ + Al Aq. 

 If, however, the lime and magnesia were taken into 

 account, and supposing them to re-place alumina, we should 

 have, according to the formula of Professor Thomson, 



3 Al S + 2 Al S2 + 3 Aq. 

 Corresponding with this composition, we find several 



analyses ; especially one by Boussingault, of a Halloysite, 

 as he terms it, from Guatequa in New Granada, found in 

 carbonaceous schist with anthracite, of a soft consistence 

 with a cheesy fracture, becoming transparent in water ; and 

 two of Kaolin by M. Berthier. 



Halloysite from Kaolin. 



Guatequa.* St. Yriex.f Schneeberg.t 



100-0 99-6 95-4 



It is quite obvious that these correspond with the formula 

 which we have already given. The halloysites of Berthier 

 differ essentially in their external character from tuesite 

 The specimen from Anglar, near Liege, possesses a density 

 of 1-8 to 2-00, or, according to Ingelspach Lariviere, from 

 1-82 to 2-09.§ Fracture compact, waxy, conchoidal, pure 

 white or blueish, scratched by the nail, taking a polish 

 under the finger. It is found in veins of hydrate of iron 



♦ Ann. de Chim., liii. 439. 

 t Traite des Essais par la Voie Seche par M. Berthier, i, 58. 

 § Ann. des Mines, v. 3l0. 



tib. 



