112 UNIVERSITY OF COLORADO STUDIES 



At the surface the monzonite is very generally jointed, often in 

 prismatic blocks which stand on end. Not infrequently these are six 

 feet long and may reach a length of ten feet. These blocks usually 

 have the two widest sides parallel, and to be of service as building stone 

 many would require dressing on only the two ends or the two ends and 

 one edge. These longest blocks occur only near the center of the 

 largest stock; near the borders the blocks are much more irregular in 

 shape. The possibility of too frequent jointing, aside from the small 

 "knots," or segregations, which for ordinary purposes are negligible in 

 amount, is probably the only objection to the rock as a building stone. 

 Its fine texture makes it easily workable and practically removes the 

 danger of disintegration through differential expansion. The relatively 

 small amount of ferromagnesian constituents eliminates the probability 

 of excessive iron stain and rapid decay. The color is attractive and 

 but little changed on surfaces longest exposed to weathering. For 

 monumental purposes the monzonite would take a high polish, and on 

 polished surfaces lettering would show distinctly as evidenced by the 

 white edges on trimmed specimens due to minute fracturing of the 

 colorless minerals. 



Microscopic Petrography. — Feldspar is by far the most important 

 constituent, orthoclase and plagioclase being nearly equal in amount. 

 There is a decided tendency toward idiomorphism on the part of the 

 plagioclase crystals, and zonal structure is pronounced. More calcic 

 zones alternate with more sodic, and three to five bands of each may 

 appear in a single crystal. In sections normal to (oio) the highest 

 angle measured was 26 , indicating the presence of labradorite, but it is 

 probable that the greater part of the plagioclase is more sodic than this. 

 The prevailing albite twinning is sometimes accompanied by pericline 

 and less often by Carlsbad twinning. The plagioclase is generally very 

 fresh, but is occasionally kaolinized, and more often saussuritized. In 

 this case the "saussurite" appears to be in large part epidote. 



The crystallization of pyroxene, hornblende and biotite was in large 

 part synchronous since intergrowths of any two or all three are present. 

 While the crystallization was in part contemporaneous with the forma- 

 tion of plagioclase, the ferromagnesian minerals did not usually reach 



