72 NOTES ON THE MINERALS FOUND NEAR BRISTOL. 



ZINC. 



This metal occurs in this neighbourhood as Carbonate^ the 

 mineralogical name of which is Calamine. It is generally coloured 

 by the presence of oxide of iron, varying from a pale salmon 

 colour to a full red. It was formerly obtained plentifully at 

 Shipham, and many parts of the Mendips, but tlie supply is now 

 nearly exhausted. In the Museum may be seen specimens from 

 West Harptree. The discovery of a new deposit will be most 

 important, and will amply repay the finder, as the present market 

 is dependent on South American, Spanish, and other foreign 

 localities. In a few places the calamine is quite white and free 

 from iron. 



I would remind the young collector that calamine may be easily 

 distinguished by the blowpipe on charcoal by the peculiar sublimate 

 that changes from yellow to white on cooling. 



One of the Harptree specimens gave on analysis : — 



Zinc Carbonate ... ... ... 94.98 



Ferric oxide ... .. ... 4. 11 



Silica and insoluble matter ... ... 0.19 



Calcic Carbonate ... ... ... 0.72 



100.00 



Zinc ... ... 49.4 % 



MAGN^JSIUM. 



In our neighbourhood we have Carbonate of Magnesium 

 frequently occurring, but differing considerably in its physical 

 aspect. At Clifton we have thick beds of conglomerate made up 

 of fragments of older rocks cemented together by magnesian 

 compounds. The Carbonate of Magnesium never occurs in a 

 pure state, but always mixed with Carbonate of Calcium, forming 

 what is called DolomJte, (Ca. Mg. 2 CO3). In the Clifton 

 Dolomite from 2 to 6 per cent, of Ferric oxide is present. At 

 other places, as is typically exemplified by a remarkable deposit at 



