10 PHYSIOGRAPHY. 



Alum-stone Amber. 



Brittle. Hardness =5-0. Sp. gr. =2-694 (a crystal- 

 lized Variety from Tolfa.) 



Compound Varieties. Massive : composition small 

 granular, often impalpable ; fracture uneven, flat conchoi- 

 dal, splintery, sometimes earthy. 



1. Alone, in the matrass, before the blow-pipe, it at first disengages 

 moisture ; but a more intense heat occasions a sublimate of sulphate of 

 ammonia. The crystals decrepitate with great energy when heated, and 

 become reduced to powder like Diaspore. Upon charcoal in a strong 

 heat it contracts, but does not melt. It dissolves however, in borax, 

 with effervescence, and gives rise to a colorless and transparent glass. 



2. Analysis. 



By VAUQUELIN. ByCoRDiER, 



of the crystals. 



Alumina . . 43-92 . . . 39-654 



Silica . . 24-00 . . . 0-000 



Sulphuric acid . . 25-00 . . . 35-495 

 Potash . . 3-08 . . . 10-021 



Water . . 4-00 and loss 14 380 



a trace of oxide of iron. 



3. Alum-stone is found at Tolfa near Civita Vecchia,in the vicinity of 

 Rome ; also in Tuscany in the kingdom of Naples, and in the county of 

 Beregh in Hungary. According to CORDIER, it exists in almost all 

 burning volcanoes. It seems to form beds of greater or less extent, chief- 

 ly made up of the massive varieties, in which small cavities occasionally 

 present themselves lined with the crystals, which are always very mi- 

 nute. 



* 4. It is employed in the manufacture of alum ; and the superior qual- 

 ity of that from Tolfa has been ascribed to this mineral. 



AMALGAM. (See Native Amalgam.) 

 AMAZON STONE. (See Feldspar.) 

 AMAUSITE. (See Petrosilex.) 

 AMBER. Yellow Mineral-Resin. MOHS. 

 Irregular forms, grains and spheroidal masses. 



