THE NONMETALLIC MINERALS. 473 



agglomeration of pumice and dust of a glaring white colour, cut by the action of rain 

 and wind into fantastic shapes, stands out against the blue sky like the irregular 

 crags, spurs and ridges of a great glacier. 



Along the marina are quantities of pebbles of pumice, either rounded by the 

 torrents that descend from above or by the waves that lap the shore. When the 

 wind blows from N. E. a veritable fleet of floating masses reaches the port of Lipari. 

 The pumice that has been excavated is carried to the beach, and stored and sorted 

 in sheds or caves cut out of the same pumice tuff, protected in front by a breakwater 

 of big stones to prevent heavy seas reaching and washing away the produce. 



Pumice in commerce is classified as follows grosse( large size), correnti (medium), 

 andpezzani (small) ; the large and middle size are subdivided into lisconi (flat) and 

 rotondi (round) . The lisconi are filamentous and break less easily than the rotondi. 

 They are also trimmed by the sorters. The lisconi. and rotondi are again subdivided 

 into white, black, and uncertain, according to their colour. 



The price varies according to the quality from 50 to 2000 lire the ton. The 

 common price for the assorted is 350 to 500 lire the ton. As much as 5000 tons a 

 year are exported. The best pumice is that of Campo Bianco. It is also obtained at 

 Perera, but it is in small quantity and was produced at the eruption of the Forgia 

 Vecchia. It is a first class grey pumice and fetches from 600 to 750 lire the ton, and 

 does not so easily break as the Campo Bianco. Also at Vulcano a grey pumice 

 is found but the presence of included crystals render it useless for commercial pur- 

 poses. At Castagna a commoner pumice is obtained called Alessandrina, of which 

 brick shaped pieces are made and used for smoothing oil-cloth. 1 



According to the Engineering and Mining Journal 2 a merchantable 

 pumice has recently been found in Miller County, Idaho, but the 

 demands for material of this nature is likely to be lessened by the 

 putting upon the market of a German artificial product. In 1897 some 

 1,700 tons of pumice were mined near Black Rock, Millard County, 

 Utah. 



Ground and bolted pumice is quoted as worth from $25 to $35 a ton 

 according to quality. 



3. ROTTENSTONE. 



The name rottenstone has been given to the residual product from the 

 decay of silico-aluminous limestones. Percolating carbonated waters 

 remove the lime carbonate from these stones, leaving the insoluble 

 residue behind in the form of a soft, friable, earthy mass of a light 

 gray or brownish color, which forms a cheap and fairly satisfactory 

 polisher for many metals. Specimens Nos. 54150, 54153, 67390, 67791, 

 U.S.N.M., show the material in its natural state and ground and bolted. 



The chemical composition of rottenstone, as may well be imagined 

 from what has been said regarding its method of origin, is quite 

 variable, though alumina is always the predominating constituent. 

 Analyses show: Alumina, 80 to 85 per cent; silica, 4 to 15 per cent; 



1 The South Italian Volcanoes, by H. J. Johnston-Lavis, Naples, F. Furchheiin, 1891, 

 pp. 67-71. 



2 Volume LXIV, July 24, 1897, p. 91. 



