310 GEOLOGY OF THE DENVER BASIX. 



crystals commonly found in the minettes of < J-ermany. In the finer-grained 



rock augite is less frequently developed in good crystals, and there especially 

 is the appearance of a rhombic pyroxene noticeable. The latter is faintly 

 but distinctly pleochroic, exhibits parallel extinction, possesses pinacoidal 

 as well as prismatic cleavage anil cross-fissures from which a fibrous alter- 

 ation product extends, and is more nearly free from inclusions than the 

 accompanying augite. 'The rhombic mineral is not abundant in any case. 

 It is presumably less rich in iron than the hypersthene of the andesites, 

 and is hence to be considered as bronzite. Green hornblende occurs in 

 small, irregular grains in the compact rock and also intergrown with augite 

 in the outer /one of a few crystals. Occasionally it surrounds the augite. 



The biotite is of dark-brown color and occurs in small, irregular leaves 

 often attached to pyroxene grains and containing many inclusions of 

 magnetite. 



Apatite is very abundant. Its prisms included in augite and the 

 stouter free crystals are decidedly pinkish in color, with distinct pleochroism. 

 The smaller prisms are often colorless. Magnetite is present in small 

 amount in the usual grains. Quartz appears only in the finer-grained rock, 

 in very small, angular particles as the last product of consolidation, and in 

 very insignificant quantity. 



chemical composition. — The compact rock, in quite fresh condition, was 



analyzed by Mr. L. G. Eakins, with the following result: 



Analysis of augite-mica-syenite from the north fork of Turkey Greek, Jefferson County, 



Colo. 



SiOs 56. 90 



TiO 19 



\\<>. 18.50 



Fe.0 3 17 



I Vo 4. til 



Mno Trace. 



CaO ti- 1 ~ 



MgO r.. i<» 



K O Ill 



Na-0 2.99 



no 51 



I '" 79 



CI Trace. 



100. 07 

 Sp. gr. at 29.5 C, 2.857. 



