44 



rF.NTTI KSKOr,A. 



M.-N. Kl. 



IIk' eclogite-gabljio ol Komsdalshorn has a composition not very usual 

 in gabbroid rocks, i)(ing ciiaractcri/ed by the prevalence of ferrous iron 

 over magnesia. In Washington's Tables we find, however, a number of 

 nearly identical analyses. Most of them are of r)livine-bearing rocks, as 

 e. g. a ti-o(tolitc from Anabohitry, Madagascar, described by A. Lacroix ' 

 But some are devoid of olivine, e. g. many gabbros and norites from the 

 Adirondack Region, described by j. F. Kemp-^. TIk ir minerals are labra 

 doritc, hypcrsthent-, garnets, green augite, l>ro\vn hornblende, biotite 

 magnetite, apatite. It is noteworthy, that these rocks also contain garnet 

 being in them of a posterior origin. This mineral here apparently takes 

 tJK' place of tlu' olivine in so far as it contains orthosilicates. As we will 

 set forth later, the high proportion of ferrous oxide is favourable for the 

 growth of late garnet as well as for the preservation of primarv garnet, 

 which in all such cases belongs to the almandite series. 



The iiiineralogical composition of the eclogite-gabbro being verv 

 complicated, no mode can be calculated. The garnet and the clino- 

 pyroxene apparently are the most abundant constituents, after which 

 follow plagioclase, hornblende, biotite and ilmenite. Apatite 

 and rutile are minor constituents. 



The garnet, separated by means of Clerici's solution, was analyzed 

 by the writer with the following result: 



Sp-g. = 3-97- 



"d =" I-7965- 

 RO : R,_X\ : SiO.3 - 2.99 : i : 3.08. 

 Composition: (Fe6iMniMgo(,Caij.)3(Alg<)Feii)o. 



' A. Lacroix, Bull. Soc. France Min. 1908, 323. 

 2 J. F. Kemp, U. S. G. S. Bull. n:o 168, 1900, 37. 



