470 REPOKT OF NATIONAL MUSEUM, 1899. 



According' to Renard,^ the celebrated Belgian razor hone quarried 

 at Lierreux, Sart, Salm-Chateau, Bihau, and Kecht is a damouritc 

 .slate containing innumerable garnets, more than 100,000 in a cubic 

 millimeter. Like the Katisbon hone, this occurs in the form of thin, 

 yellowish bands, some 6 centimeters wide (2f inches) in a blue-gray 

 .slate (phjllade). The bands are essentially parallel with one another 

 and with the grain of the slate, into which they at times gradually 

 merge. The chemical composition of a sample from Recht is given 

 a.s below. The mici'oscopic structure of the stone as described and 

 figured by Renard is essentially the same as that of the Ratisbon stone 

 in the collection of the U. S. National Mu.seum (see Plate 30, fig. 2), 

 and the stones are practically identical in color and texture as well. 



Silica (SiOj) 46.5 



Titanic oxide (TiO^) 1.17 



Alumina (AI2O3) 23. 54 



Ferric iron (Fe^Og) 1. 05 



Ferrous iron (FeO) 0. 71 



Manganese oxide (MnO) 17.54 



Magnesia (MgO) 1. 13 



Lime (CaO) 0.80 



Soda (Na^O) 0. 30 



Potash (K2O) 2.69 



Water (H^O) 3. 28 



Carbon dioxide (CO^) 0. 04 



Phosphoric acid (PjOj) 0. 16 



Sulphur (S) 0.18 



Organic n)atter 0. 02 



Total 99. 11 



The cutting property of the stone would appear to be due to the 

 presence of the small garnets above noted. (Specimens Nos. 38938- 

 38940, U.S. KM.) 



The .so-called holystone is but a fine, close-grained sandstone of the 

 same nature as that used in grind and whet stones. The greater part 

 of those made in this country are from the Berea sandstone of Ohio, 

 though some are said to be imported from Germany. The stones are 

 used mainly on shipboard, and the trade is small. 



2. Pumice. 



The material to which the name pumice is commonly given is a form 

 of glassy volcanic rock, which, by the expansion of its included moist- 

 ure while in a molten condition, has become, like a well-raised loaf, 

 filled with air cavities or vesicles. The cutting or abrasive quality 



^ M^moires Couronn^s et M^moires des Savants Etrangers de L'Academie Royal des 

 Sciences, etc., Belgique 1878, pp. 1-44. 



