108 Penfield and Foote — Composition of llmenite. 



a, 100 

 c, 001 



m, 110 d, 201 

 h 12 ° /> ° 21 

 3. 



2/, 041 

 o, 221 



77/ 



771 



i>"7 ;a 



777 



a m 



The prevailing types of the crystals are shown in figs. 2, 3, 

 and 4. Some of the crystals are more than 4 cm long and are 

 transparent and colorless ; a few have a delicate wine color, 

 and many are either opaque white or partially so. The opaque 

 crystals, as shown by microscopic examination, are not pseudo- 

 morphs but consist of fresh unaltered topaz containing minute 

 quartz crystals, which evidently have been included during 

 crystallization. 



Associated with the topaz crystals are rough trapezohedrons 

 which apparently were once garnet, but which have suffered 

 alteration. The garnet is wholly gone and the crystals consist 

 of bixbyite with either quartz, topaz or both. The garnet was 

 probably the manganese variety, spessartite, which has been 

 observed by Cross* at Nathrop, Colo., associated with topaz in 

 rhyolite, an occurrence similar to that in Utah. 



Aet. XIY. — Note concerning the Composition of llmenite * 

 by S. L. Penfield and H. W. Foote. 



The existence of a molecule E IJ . R IV 2 in bixbyite and 

 perofskite brings to mind the views concerning the composi- 

 tion of ilmenite. One of these is, that the mineral is RO . Ti0 2 

 (R=Fe and Mg), as advanced by Mosanderf and adopted by 

 RammelsbergJ and Hamberg.g The other, that it is R 2 8 , or an 

 isomorphous mixture of Fe 2 3 and Ti 2 3 , as advanced by Rose|| 

 and adopted by Groth.^f 



* This Journal, xxxi, p. 432, 1886. f Pogg. Ann., xix, p. 219. 



± Pogg. Ann., civ, p. 49*7. 



k Geol. Foren., i, Stockholm Forhandl., xii, p. 604. 



|| Pogg. Ann.. Ixii p. 119. 



\ Tabellarische Ubersicht der Mineralien, 3 Aufl., Braunschw., 1889, p. 40. 



