HYDROUS SILICATES — MARGAROPHYLLITE SECTION. 31J 



The Xew Jersey clay-beds of the Cretaceous formation are 

 mainly kaolinite, and have been thus formed. In other 

 eases permeating waters have washed out the oxides of iron 

 present, and have left the white clay in place. A pure 

 kaolinite bed occurs at Brandon, Vermont, along with a 

 limonite bed, where the rock decomposed was probably a 

 feldspathic hydromica slate. Most of the limonite beds of 

 Western New England afford kaolinite ; yet it is generally 

 more or less colored by iron oxide. 



Common clays consist of finely-powdered feldspar, quartz, 

 and other mineral material, with often more or less kaoli- 

 nite. They burn red in case they contain iron in the state 

 ordinarily present in them of iron carbonate, or hydrous 

 iron oxide (limonite), or in combination with an organic 

 acid, or in some other alterable state of composition, heat 

 driving off the carbonic acid or water, or destroying the or- 

 ganic acid, and so leaving the red oxide of iron (or sesqui- 

 oxide), or favoring its production. But the iron may be so 

 combined as not to give the red color ; and this has been 

 found to be true with the clays from which the cream-col- 

 ored Milwaukee (Wisconsin) brick are made, and that of 

 other clay beds in that vicinity. The iron may be there in 

 the state of the silicate, zoisite, or epidote. 



Pure kaolinite (or kaolin as it is ordinarily called) is 

 used in making the finest porcelain. For this purpose it is 

 mixed with pulverized feldspar and quartz, in the proportion 

 needed to give, on baking, that slight incipient degree of 

 fusion which renders porcelain translucent. The name 

 kaolin is a corruption of the Chinese word Raiding, mean- 

 ing high ridge, the name of a hill near Jauchau-Fu, where 

 the mineral is obtained; a.Yidit\\Q petuntze (pch-tun-tsz) of the 

 Chinese, with which the kaolin is mixed in China for the 

 manufacture of porcelain, is, according to S. W. Williams, 

 a quartzose feldspathic rock, consisting largely of quartz. 

 The word porcelain was first given to China-ware by the 

 Portuguese, from its resemblance to certain sea-shells called 

 PorceUana; they supposed it to be made from shells, fish- 

 glue, and fish-scales (S. W. Williams). 



The impure kaolin is used for stoneware and fire-bricks. 

 The presence of iron, in any state, makes a clay more or 

 less fusible, and therefore an unfit material for fire-bricks. 

 But a little of it exists in all clays employed for making or- 

 dinary bricks, and hence their red color. 



