New Occurrence of Rutile and Sapjphirine. 265 



Megascopically, the ihnenite rock from this occurrence con- 

 sists essentially of a dense black, medium to rather coarsely 

 granular ilmenite, through which are scattered small grains of 

 feldspar, or its decomposition products, occasional grains of a 

 dark green spinel, and plates of dark brown mica. Long 

 exposure to surf ace weathering develops a brown limonite coat, 

 but, as a whole, the ilmenite rock is very resistant to weather- 

 ing processes. The ore, studied in thin sections and on pol- 

 ished surfaces, shows that the ilmenite, as well as the other 

 constituents, lack altogether any crystallographic outlines. 

 The ilmenite grains range in size from individuals 3-4: mm in 

 cross section to ones 10-12 min , the average being perhaps 6-T mm . 

 The feldspar is the same variety as that in the anorthosite and 

 forms rounded grains. It is often largely replaced by second- 

 ary products. Lying along the border of many of the feldspar 

 grains, next to the ilmenite, biotite is developed. This may 

 lie parallel to the margin or may project out into the feldspar, 

 sometimes replacing a good portion of it. Its occurrence is 

 such as to suggest that it may be of later origin than the feld- 

 spar, developed, perhaps, during the late magmatic period, or 

 during a subsequent period of metamorphism. It possesses a 

 very marked pleochroism and absorption : light brown or almost 

 colorless to deep reddish brown. The axial angle as measured 

 with the microscope was found to be 10 degrees. It resembles 

 closely mica, often observed in a somewhat similar connection 

 elsewhere, and is doubtless an iron rich variety. Alteration 

 changes it to a chlorite. The spinel is of a dull green color, 

 feebly translucent, isotropic, and is to be referred to the vari- 

 ety pleonast. Its grains are entirely without crystalline out- 

 lines, and it occurs both with the ilmenite and about the 'feld- 

 spar grains. Quantitative estimates show that considerable 

 portions of the ore will not contain over 2 to 2*5 per cent cf 

 accessories, but the general run will carry from 5 to 6 per cent. 



Structure and Composition of the Ilmenite Grains. — Exam- 

 ined with a strong direct illumination, polished surfaces of the 

 ilmenite show that individual grains are not of homogeneous 

 composition, although all are identical in character. They are 

 made up of a very fine lamellar intergrowth of two kinds of 

 material. One kind, comprising what is roughly estimated as 

 one-fifth to one-quarter of the whole, is of a bright steel-gray 

 color and follows, as a rule, a nearly straight course across the 

 grains. Many of them pinch out within the grain and in some 

 the strips have the form of very flat, lensiform bodies ; again 

 they are slightly curved in outline. In width they vary from 

 0*003 to 0'02 mm . The second series are uniformly broader 

 than the first and run from 0'036 mni to 0'09 mm in width. These 

 are of a dull black color. The whole intergrowth suggests in 



Am. Jour. Sci.— Fourth Series, Vol. XXXIII, No. 195.— March, 1912. 

 18 



