3^2 SMITHSONIAN MISCELLANEOUS COLLECTIONS [vOL. 45 



too rich in the more acid feldspars to admit of close comparison. All, 

 however, show general relationship to the Virginia type and it is 

 probable that more alkalic phases of the latter rock exist. 



Unakite^ (Cat. No. 75,518) 



This rock is an irregular crystallization of old-rose feldspar and 

 green epidote, the latter generally occupying the spaces between the 

 feldspar. The peculiar green of the epidote, together with the old- 

 rose hue of the feldspar, make a striking and beautiful combination, 

 and were the rock sufficiently abundant to justify exploitation, its 

 quarrying must certainly prove a profitable venture. As the case 

 now stands, the working of the deposit is out of the question for the 

 reason that there is not enough of it. Its use for outside decoration 

 cannot be considered, owing to the relative ease with which the 

 rose-colored feldspar bleaches to a white product. 



It has been noted that the crystallization of the feldspar, quartz, 

 and epidote is very irregular. In some specimens gathered from the 

 type locality on the eastern slope of the ridge, the red feldspar con- 

 stitutes fully three-fourths of the mass, and from this ultra-feld- 

 spathic phase, all phases through to the quartz-epidote (epidosite) 

 combination may be seen. 



Rarely an automorphic outline of a feldspar may be seen with a 

 slightly resorbed margin. The largest phenocryst noted was 2.5 cm. 

 The feldspar is specked with epidote and quartz, the former occupy- 

 ing the fissures and cleavage cracks. Where the epidote forms 

 cloud-like masses, the feldspar appears to have been bleached. 



Quartz is distributed in the spaces between the other minerals, also 

 in the body of the feldspar and epidote. It is generally clear, per- 

 haps inclined to the smoky type. It presents no unusual features, 

 and with mention of an occasional piece of iron oxide, the list of 

 macroscopic constituents ends. 



In thin section epidote, feldspar, quartz, iron oxides, zircon, and 

 apatite were seen. Epidote occurs in large granular aggregates. 

 Frequently such masses have curved boundaries. It also appears as 

 minute isolated dots in the mass of the feldspar and as stringers 

 along the cleavage planes of this mineral. This occurrence is well 

 represented in plate lxxi, a. The specks of epidote representing 



^ Although the secondary nature of this rock excludes it from proper clas- 

 sification according to the quantitative system of Cross, Iddings, Pirsson, and 

 Washington, and although it is uncertain whether the original magmatic 

 characters are retained or not, it may be mentioned that a magma of this com- 

 position would fall under the head of sagamose. 



