366 Clarice and Darton — Hydromica from New Jersey. 



This gives, as an orthosilicate, the formula 



(KH) 68 (MgFe) 24 (AlFe) 6l (Si0 4 ) 6 , 28H 2 0. 



It is evident, from these data, that the mica is one which has 

 been largely, but not wholly, altered to a vermiculite ; the 

 latter term indicating a mica in which potassium has been 

 replaced by hydrogen, and which has taken up water of crys- 

 tallization. So far as the analysis goes, the condition of the 

 water is uncertain ; for it was determined in two fractions 

 only, at and above 100°, whereas more fractions are needed for 

 accurate diagnosis. Some crystalline water may be retained 

 far above 100°, so that the loss above that temperature includes 

 part of this fraction plus all the water of constitution. Apart 

 from this uncertainty the ratios reduce easily in terms of the 

 mica theory to the following molecular mixture : 



^Si0 4 EEKH 2 ^Si0 4 = H, J3i0 4 = R"H 



3 Al— Si0 4 = Al + 6R'"— Si0 4 = R'" + 5R'"— Si0 4 = R"H 3 aq. 

 ^Si0 4 = Al ^Si0 4 = R'" ^Si0 4 = R"H 



Calculating with the atomic ratios Al : Fe 7// : : 2 : 3, and Fe f/ : 

 Mg : : 3 : 7, we have the following comparison between analysis 

 and theory : 



Keduced. Calculated. 



Si0 2 40-24 40*55 



A1 2 3 10-34 10-51 



Fe 2 3 24-57 24-71 



FeO 5-21 5-21 



MgO 6-78 6-75 



K 2 2-20 2-27 



H 2 0, 100° 3-03 Crystalline 4-34 



HO above 100° 7-63 Constitutional 5-66 



100-00 100-00 



In short, the mica consists of muscovitic and phlogopitic mole- 

 cules in the ratio of 9:5. 



9R'" 3 (Si0 4 ) 3 R' 3 , 

 5R'"(Si0 4 ) 3 R" 3 H 3 ,3aq. 



The mineral is evidently an unusual mica, differing widely 

 from any other hitherto described. Its very high proportion 

 of ferric oxide is its chief characteristic, and suggests a ferric 

 muscovite as one of the antecedent, unaltered molecules. Such 

 a muscovite is theoretically conceivable, but is not actually 

 known. 

 Laboratorj' U. S. Geological Survey, Feb. 18, 1899. 



