214 LARSEN AND WHERRY: LEVERRIERITE FROM COLORADO 



and 2 of Table 3 ; columns 4 to 8 give analyses of other members 

 of the same group of minerals for comparison. The "name 

 leverrierite has been selected for the group because it has priority 

 over all the others except kryptotile, which is, however, only 

 known in indefinite mixtures. 



All the minerals shown in the table are essentially silicates of 

 aluminium with some Fe 2 3 and RO. Assuming that the Fe 2 3 

 and RO replace A1 2 3 , the ratio A1 2 3 : Si0 2 varies from 1.86 

 to 3.95. The H 2 0+ and the total H 2 also vary considerably, 

 but no more than might be expected from determinations made 

 under widely different conditions. Kryptotile is reported as 

 having 7.70 per cent of H 2 0. If this represents total water, it 

 contains considerably less than the others. Batchelorite, 

 kryptotile, rectorite, and the original leverrierite are near to 

 A 1 2 3 .2Si0 2 .2H 2 in which about half the H 2 is given off below 

 110°. The Colorado mineral is nearer to Al 2 3 .3Si0 2 .4H 2 

 and about two-thirds of the water is given off below 110°; while 

 delanouite is near Al 2 3 .4Si0 2 .6H 2 0. However, there appears 

 to be an almost continuous variation of the ratio A1 2 3 : Si0 2 

 from 1.86 to at least 2.76. This can hardly be due to admixed 

 impurities, as the authors have examined the Colorado mineral 

 and the type rectorite, and have found them essentially homo- 

 geneous, and the descriptions of the analyzed leverrierite and 

 batchelorite also indicate homogeneous material, although the 

 delanouite examined by the authors contained some mpurity 

 while the description of the analyzed kryptotile indicates impure 

 material. This variableness in composition within definite 

 limits suggests that a mineral group is represented, or at least a 

 species including several subspecies, as is the case, for instance, 

 with muscovite. This view is confirmed by a comparison of the 

 properties of the several minerals in Table 4. 



The optical and physical properties of the six minerals, while 

 not identical, are about as nearly alike as are the corresponding 

 data for various specimens of muscovite and other complex 

 minerals; and as in muscovite, the cleavage, optic orientation, 

 optic character, and birefringence show comparatively little 

 variation, while the axial angle and indices of refraction vary 



