MINERALS FROM LYON MOUNTAIN, CLINTON COUNTY 59 



of the fact that the presence of (o . 13 . 13 .4) has already been noted 

 with reference to this type. No satisfactory reading could, how- 

 ever, be obtained. 



The crystals which measure from 3 mm to 25 mm in length are,, 

 in some instances, tilled with microscopic inclusions of quartz, 

 hematite and matted byssolite, the latter forming a central nucleus 

 of irregular shape, while the hematite, which was connected with 

 a later stage of the crystal growth, appears in the outer layers in 

 dendritic bunches. 



Regarding the generation of calcite of this type it must be un- 

 questionably placed at the base of the calcite series as shown at 

 Lyon Mountain. The marked absence of pyramidal forms in the 

 crystal habit and the presence of two modifying rhombohedra 

 entirely absent from the varied types found in the later calcite 

 deposition, set it distinctly apart as marking a separate genetic 

 phase. At the same time the close association with primary- 

 minerals which show evidences of corrosion, points to the origin of 

 this type from a highly corrosive crystallizing solution, rich in 

 carbonate of lime but still far from saturated with silica and iron. 



Type II. Calcite crystallizing in the forms of type II occurs 

 incrusting the surface of joints in the ore body, in a confused ag- 

 gregate of translucent, milky white crystals which exhibit none 

 of the tendency toward parallel grouping of separate individuals 

 noticeable in other types from this locality. The manner of the 

 crystal massing suggests rapid deposition from a solution whose 

 condition of concentration had been influenced by sudden cooling,, 

 change of pressure or some allied cause. Such a change of condi- 

 tion of concentration seems highly probable in the case of an open 

 joint rilled or partly filled with the crystallizing solution which 

 from the nature of the case would be far more sensitive to the- 

 influence of currents. 



The crystals of this type [fig. 6a-6b] which average 7 mm in 

 diameter, are rhombohedral in habit and composed of "built up" 

 forms, the predominating negative rhombohedron being deeply 

 grooved by incipient modifications parallel to (0001) and (01 12).. 

 The rhombohedron Y (0.19. 19. 13) is present as a series of moder- 

 ately brilliant but somewhat rounded faces; the form was deter- 

 mined by averaging the readings taken on 20 of the best crystals- 

 available. The scalenohedron (J: (2461) is present, beveling the 



