''tin Amphibole and Pyroooeru group 



bon to blue araphibole identical in properties with that de- 

 scribed from the dike-rock. Additional growths are not 

 developed in this case. 



U i\<n'> nor seem necessary to illustrate the relationship 

 between these amphiboles in order to establish the secondary 

 character of the bine variety. There can scarcely beany more 

 typical examples of the passage of one mineral into another 

 i^ allied character by gradual molecular replacement, than are 

 afforded by the change in question. It is not spoken of as 

 paramorphosis, because identity of chemical composition is not 

 at all probable, l>nt tin 4 outward appearance of transition i> 

 directly comparable to the change, often seen, from brown to 

 en hornblende. All quantitative stages of the replacement 

 of the common hornblende by the blue may be observed to 

 the point where the former has wholly disappeared, and beyond 

 this to the replacement of the blue amphibole itself by calcite 

 and quartz, or by the green pyroxene to he described. 



The mineral which has been referred to as green pyroxene 

 in alteration product of the blue amphibole, and as 

 a new formation in small prisms and needles in feldspar, or in 

 the secondary calcite and quartz grains. Further, it appears in 

 the Bmall olive-green pebbles as a decomposition product of an 

 unknown, yellow mineral, occurring in fibrous strings similar 

 to the forms often assumed by chlorite. Its secondary origin 

 is also most (dearly shown in a pebble of hornblende- diorite 

 which is traversed by narrow fissures mainly filled by calcite 

 and quartz, hut also containing prisms of the green pyroxene, 

 appearing as oriented extensions of hornblende prisms crossed 

 by the crack, and in needles lying free in the calcite grains. 

 The designation of this mineral as a pyroxene rests upon the 

 visible crystallographic orientation with regard to the blue and 

 en amphiboles, its crystal form as seen in free individuals, 

 and its close agreement in properties with certain members of 

 the pyroxene group. In cross sections of blue amphibole and 

 the green mineral the latter is Been to have two cleavages of 

 equal prominence, intersecting at an angle of about S T , and 

 related to the of the amphibole as would he normal for 



an intergrown pyroxene. In length sections the traces of the 

 cleavage planes are parallel to the vertical axis. e. Free prisms 

 of the mineral do not exhibit pinacoidal planes and the termin- 

 ations are sharp pointed combinations of pyramids, with ortho- 

 domes in some case- at least. The Color of the mineral is clear 

 emerald-green in prisms <»-<»o"" in thickness. 'Hie axis of 

 gre lasticity. a. i- within a very few degrees of the ver- 



tical axis, 6 : that of least elasticity, c. is also in the plane of 

 symmetry, assuming the orientation to he that indicated by 

 the intergrowth with amphibole. The pleochroism is quite 



