New Occurrence of Riotile and Sapphirine. 277 



siderable portion of one of these masses, rntile is an essential 

 and abundant constituent (ca. 15 per cent). In such there is 

 also present a smaller (3-5 percent) amount of the rare mineral 

 sapphirine. The latter may be very abundant in certain limited 

 portions of the rutile-bearing rock where plagioclase is also 

 more abundant. It is intimately associated with the feldspar, 

 commonly lying about its grains, often as a narrow band, and 

 separating it from the ilmenite. Rutile is also present with 

 ilmenite and biotite in a stringer of anorthosite closely associ- 

 ated with the rutile-bearing ilmenite rock. 



III. — The rutile-sapphirine-bearing rock forms quite sharply 

 defined portions of the ilmenite rock and appears to be of mag- 

 matic origin, representing a part of the segregation exception- 

 ally rich in titanic oxide, to a less extent in magnesia and 

 alumina, and deficient in silica. 



IY. — A new occurrence of sapphirine is recorded and in a 

 new association. Although possibly of metamorphic origin , 

 like the sapphirine in the two occurrences previously known, 

 it is thought in the present instance to be of magmatic origin. 

 A chemical analysis made on material of exceptional purity 

 shows that it resembles closely the sapphirine from the Hill 

 Tracts, Yizagapatam District, India. It is pointed out that the 

 molecular ratios derived from the analysis and from that of the 

 Indian mineral show a considerable departure from the one 

 usually accepted for the mineral, and do not correspond to any 

 simple formula, and the existence of solid solution relations 

 between the molecules making up the mineral are suggested. 



Y. — Microscopic and chemical evidence is presented to show 

 that the titanic-iron of these rocks consists of an intimate, very 

 fine, lamellar crystallographic intergrowth of ilmenite and 

 hematite, in which the hematite makes up something like one- 

 fifth of the mixture. It is pointed out that this relationship 

 suggests that the Fe 2 3 in so many ilmenites may be in large 

 part, at least, present as hematite crystallographically inter- 

 grown and not as an isomorphous mixture. 



YL— A chemical analysis of the rutile-bearing rock, also 

 quantitative estimates of the mineral composition as determined 

 with the microscope, are given. These are in fair agreement, 

 and show that the rock is unique in composition, and repre- 

 sents an extreme and new ultra-basic type of igneous rock. 

 The name TJrbainite is proposed to designate rocks of this type. 



Mineralogical, Petrographical Laboratory, 



Massachusetts Institute of Technology, 

 Boston, Mass. 



