32 



GEOLOGY AND QUICKSILVER DEPOSITS, NEW ALMADEN DISTRICT, CALIFORNIA 



FIGURE 20. Greenstone without vesicles and ouly a little altered 

 Kins* Ophltlc texture formed by radial aggregates of somewhat 

 altered andesine (and) enclosed In larger crystals of subcalclc auglte 

 (A). Dark areas are leucoxene formed at the expense of llmenite. 

 GroundmasH of altered glass consists of chlorite, nontronlte, and 

 small crystals of epldote. 



FIGURE 21. Greenstone without vesicles but with considerable al- 

 tered glass. Texture is largely inttTKranular, but some augite en- 

 velopes crystals of alblte. Made glass altered to nontronite (N). 

 Plagloclase contains minute crystals of epldote. 



rnii RC 22. Greenstone with vesicles but little altered glass. Both 

 andeslne and auglte are In thin needles forming a pilotaxltic tex- 

 ture. Vesicles are filled with chlorite locally replaced by calclte. 



23. Greenstone with abundant vesicles filled with calclte 

 (C). Section shows mlcrolltlc texture of minute laths in glassy 

 groundmass. but also contains a few pbenocrysts of alblte, replaced 

 along borders and cleavages by caleite. and still fewer equant crys- 

 tals of augtte. 



PHOTOMICROGRAPHS OF GREENSTONES OF THE FRANCISCAN GROUP SHOWING VARIATIONS IN TEXTURE, CONTENT OF ALTERED CLASS. 



AND VESICULARITY 



