58 NEW YORK STATE MUSEUM 



Hematite 



Secondary hematite derived from the magnetite occurs associated! 

 with other minerals of the second generation such as quartz, calcite 

 and albite. It is found in close aggregates of brilliant metallic 

 plates of the type shown in figure 3 the observed forms being c 

 (0001), r (ion) and n (2243). -A. phase of this habit found in 

 close association with the secondary amphibole (byssolite), is- 

 characterized by minute circular disks about 1 mm in diameter 

 consisting of flat rosettes of thin plates. These have a red metallic 

 luster resembling that of burnished copper and show bright cherry- 

 red by strong transmitted light. A specimen of quartz with which 

 these latter were associated was quite thickly covered with small 

 hemispheres of botryoidal hematite. It is quite evident from this. 

 specimen [pi. 8] that these three phases of the deposition of 

 hematite belong to the same period of genesis and were deposited 

 toward the end of the formation of secondary quartz. 



Calcite 



The several phases which mark the deposition of secondary 

 calcite are characterized by calcite crystals of definite habit. Of 

 these crystal types, the first two stand distinctly apart from a. 

 genetic point of view, whereas the last three are more or less closely- 

 related both from the standpoint of crystal genesis and habit. 



Type I. Crystals of this type are found directly associated witb. 

 the corroded quartz orthoclase and amphibole, in most instances- 

 deposited as a crust upon a highly corroded surface. They are 

 distinctly scalenohedral in habit, the steep scalenohedron M (5491/ 

 predominating, modified in termination by the rhombohedrons M 

 (4041) and E (0.13. 13.4). Figures 4a-4b and 5a-5b show this 

 habit. The rhombohedron M is present in a bright series of planes, 

 which furnished excellent points of reference. The rhombohedron 

 E, on the other hand, gave faint but distinct reflections from a 

 series of dull and somewhat rounded surfaces. On several speci- 

 mens the rhombohedron r (ion) is prominent in crystals of this- 

 habit. Several times during the measurement of crystals of this 

 type, a narrow plane beveling the acute polar edges of M (5491) was 

 observed. A rhombohedron in this zone would have the indexes 

 (0.13. 13. 2) a form which seems doubly probable in consideration 



