Knopf and Schaller — Two New Boron Minerals. 329 



Eatios Hulsite Magnetite Hulsite Magnetite 



FeO 479 ^1 392 87 ^ 4-56 K 1-01 



MgO 212 | 212 2-46 j • 



Fe„0 3 173 J> = 86 +87 }= 1-00 +1-01 



H„<J 092 j 92 1-07 



B„0 3 361 J 361 J 4-19 



The proportion of magnetite present is calculated as follows : 

 The analysis of the magnetite-free hulsite shows that the ratio 

 of Fe 2 3 : RO is 1 : 7. Therefore from the ratios of Fe 2 3 and 

 RO in the average analysis of the magnetite-hulsite mixture 

 there must be deducted such an amount (x) of both Fe 2 3 and 

 RO ( in the proportion 1 : 1 to form magnetite ) that the result- 

 ing ratio shall be 1 : 7. — ^ — L = — - in the mixture of masr- 



s RO 691 s 



netite and hulsite. Then-- - =-— - ; solving, x = 87. De- 



691— a; 1 ' to ' 



ducting 87 from both 173 Fe 2 3 and 691 RO, the resulting 

 ratio becomes 86 : 604 or 1 : 7. This mixture of minerals then 

 becomes one part of hulsite (7RO.Fe 2 3 .H„0.4B 2 3 ) with 

 one of magnetite (Fe0.Fe 2 3 ). That all the magnesia belongs 

 to the hulsite is shown by the analysis of the magnetite-free 

 mineral, which gives as the ratio of FeO : MgO = 453 : 249, 

 while that in the above analysis is 453 : 244, or practically the 

 same. The composition of the sample analyzed is then found 

 by calculation to be as follows, the formula for hulsite being- 

 taken as 9Fe0.5Mg0.2Fe 2 3 .2H 2 0.8B 2 3 . 



(Insoluble) Vesuvianite 2-24 

 Hulsite 77-40 



Magnetite 20-36 



100-00 



The density of this mixture is 4*438. Taking the density 

 of vesuvianite as 3*40 and that of magnetite as 5*17, the dens- 

 ity of hulsite is found by calculation to be 4-28. 



The ferrous iron and magnesia are doubtless not present in 

 any definite ratio, but vary reciprocally, so that hulsite may be 

 considered as a mixture of a ferrous with a magnesian borate. 

 The ratio of 9FeO : 5MgO just given is therefore only an 

 approximate one. Ferrous iron and magnesia are doubtless 

 isomorphous in hulsite as well as in paigeite, and similarly in 

 the related borate ludwigite.* Any discussion as to the 

 structural formula of hulsite would be very premature, as our 

 knowledge of such minerals is very scanty. The formula 



* An analysis of ludwigite from Montana shows this particularly well, this 

 mineral containing very little ferrous iron while that from Hungary contains 

 about 15 per cent. 



