464 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 49. 



mineral containing alumina, silica, and water. In adapting German 

 mineral names to American use the usual rule is to add ite to tlie 

 ending plian; thus, leukophan, meliphan, and rhabdophan become 

 leukophanite, mehphanite, and rhabdophanite; only e is added in 

 other cases, as allophan, glaukophan, and uranophan, which are ordi- 

 narily written allophane, glaukophane, and uranophane. For the 

 sake of miiformity, however, it seems best to have all mineral names, 

 except those which have come down to us from the ancients, end 

 in ite, so allopJianite is adopted as the name of the substance under 

 discussion. 



Composition. — Considerable disputation has been indulged in 

 during the last few years, chiefly by German mineralogists, as to 

 whether allophanite and other similar minerals are variable mixtures 

 or definite compounds. Most that has been written consists of mere 

 quibbhng over the meaning of terms; but Stremme,^ after summing 

 up the arguments on both sides, has shown that the noncrystalline 

 clay-minerals are best interpreted as adsorption compounds of 

 colloidal alumina and silica with variable amounts of water. The 

 observations described in the following paragraph confirm the cor- 

 rectness of this view as far as one sample of allophanite is concerned. 



A new occurrence of allophanite. — Material sent to the Musemn for 

 identification labeled as occurring ''20 miles from Salt Lake City, 

 Utah," proved to correspond in most of its properties with allo- 

 phanite.^ But its refractive index did not agree with that given in 

 the books for this mineral (1.49), and as the exact nature of the 

 mineral on which this value was determined is not recorded, further 

 study of the matter seemed desirable. 



The following are the properties of the sample in question : 



Color: White to yellowish white. 



Luster: Vitreous to dull; sub transparent. 



Hardness: 3. Sp. gr.: 1.88 to 1.90. 



Structure: Granular. 



Fracture : Subconchoidal. 



Optical properties: Isotropic (amorphous, colloidal) in large part, 

 also showing confusedly anisotropic (metacoUoidal) patches. 



Index of refraction : 



Observed. Calculated. 



Saturated with HgO (HgO about 45 per cent) 1. 465 1. 466 



Air-dried 40 per cent 1. 480 1. 479 



Dried at 120° 10 per cent 1. 565 1. 564 



Ignited per cent 1.595 1.592 



The calculated values were obtained as follows : The indices of the 

 three constituents being (amorphous forms) AI2O3 1.68,^ SiOj 1.46, 



1 Doelter's Handbuch der Mineralchemie, vol. 2, pt. 2, 1914, p. 36. 



2 Cat. No. 87438, U.S.N.M. 



' An approximate determination on ignited Al(OH)g. 



