Chemical Compositiou. 



The analysis was made by Mr. Chr. Christensen, cand. 

 polyt., with the following result: 



Theo. 

 SiOrj 29,62 per ct. 29,36 per ct. 



Fe^O.^ 19,48 — 19,55 — 



FeO 33,28 — 35,20 — 



MnO 2,20 — 



CaO 14,38 — 13,69 — 



H^O 2,24 — 2,20 — 



101,20 per ct. 



The theoretical values have been calculated from the formula 

 ' II III 



HCaFe^FeSi^OQ, and, as it will be seen, they agree very well 



with this formula. 



The manganese content, as shown by Bauer^) is of much 



interest in the ilvaite, as compared with the axial ratios. By a 



rising MnO content the lengthes of the a- and c-axes increase 



in proportion to the è-axis; this feature holds also good, when 



the present occurrence is taken into the comparison: 



Elba 0,74—1,55 MnO 



Kangerdluarsuk . 1,97 MnO 



Siorarsuit 2,20 MnO 



Herbornseelbach 6,78 — 8,68 MfiO 



a\b:c = 0,6665 : 1 : 0,4427 



a:b :c = 0,6744 : 1 : 0,4484 



a:b:c = 0,6766 : 1 : 0,4499 



a:b:c = 0,6795 : I : 0,4576. 



In the ilvaite from Thyrill in Iceland the axial ratios are : 

 a : b : с = 0,6619 : I : 0,4390 ; with regard to this locality we 

 should thus have to suppose a very slight manganese content 

 or none at all. 



If the ratio between the a- and c-axes is calculated, quite 

 corresponding alterations are found, viz. 



Beiträge zur Mineralogie: Neues Jahrbuch f. M. I.Band, 1880, pag. 47. 



