648 PROCEEDINGS OF THE AMERICAN ACADEMY. 



Hmenite. Ilmenite in the form of thin bent plates is one of the fa- 

 miliar minerals in secondary veins at the emery bed at Chester. A 

 phase of the alteration of such a plate to rutile and magnetite was ob- 

 served in several specimens. The mass of the plate is changed to dull 

 massive rutile, and tiny brilliant octahedral crystals of magnetite are 

 grouped in parallel strings on its surface. Sagenitic rutile in orientated 

 groups on ilmenite plates was also observed. 



A second type of ilmenite was discovered in the form of exceedingly 

 brilliant tiny crystals implanted on acicular diaspore in open or calcite- 

 filled cavities. These crystals do not exceed 0.5 mm. in diameter, but 

 attracted attention by their adamantine lustre, which caused them to be 

 mistaken for brookite at first. There is little doubt in the authors' 

 minds that the brookite long since reported from Chester by Shepard 

 and not afterwards observed there was of the same nature as these tiny 

 ilmenite crystals. They are thin, tabular parallel to the base, and are 

 attached by an edge of the table. The base is marked by triangular 

 striations, but, like all the faces, reflects the signal well considering its 

 minute size. Measurement of a number of them revealed the same 

 forms on all: c (0001), a (112"0), r (10T1), s (0221), n (2243), 

 Di (2323). These forms are shown in Figure 9 in average development ; 

 there is considerable variation in the relative size of the different forms 

 on different crystals. 



Shepard in his report on the emery mine 6 refers to the occurrence 

 of large crystals of ilmenite (called by him Washingtonite) in white 

 quartz veins within a mile of the northern end of the vein. 



Concerning this occurrence Emerson 7 makes the following statement : 

 " There were in the Shepard collection at Amherst, destroyed by fire, 

 great tabular crystals 6 to 8 inches across and 1 inch thick of model- 

 like perfection from the locality mentioned above. They were tabular 

 by the predominence of OP. I cannot find that they were ever 

 described by Professor Shepard." 



While in Chester in 1904 the senior author secured from an old local 

 collection a specimen which clearly represents this " lost locality " and 

 which seems worthy of description. It consists of two attached crystals, 

 three and two inches across and half an inch thick, partially embedded 

 in glassy white quartz. The crystals are dull black and more or less 

 covered with scales of rusty mica. They show the forms c, a, r, and n, 

 very sharply developed in about the proportions of the accompanying 

 figure 10. No further information as to the exact location of the vein 

 which yielded the ilmenite crystals was secured. 



6 Reprinted in Monograph, 29, pp. 122-135. 



7 A Mineralogical Lexicon, p. 107. 



