J922] A Magnetite-Marble Ore at Lansing, N. C. 143 



marble rock in large masses that enclose particles of the other com- 

 ponents. Some of the particles are plainly large skeleton cubes, poiki- 

 litically developed. In other words, they possess the sieve structure 

 which is characteristic of minerals formed later than the rock in which 

 they are found. In some cases the pyrite apparently replaces calcite 

 and in other cases magnetite. It is believed that it was not a part of 

 the original rock but was subsequently introduced. 



Veins in the Ore : — In places fine-grained feldspar-quartz veins cut 

 the hornblende-magnetite masses. In thin section the vein rock 

 is seen to be badly crushed — the quartz areas are aggregates of small 

 quartz grains and the former feldspar grains are now aggregates of 

 small, Yevy light yellow epidote grains. There are, however, no sharp 

 boundaries between the feldspar and the quartz areas. These have 

 been obliterated by the crushing. The quartz areas near their borders 

 are full of epidote grains and the epidote areas contain nests of quartz 

 grains and, further within their interiors, individual grains of quartz. 

 Moreover there are little veins of epidote in the quartz, and vein-like 

 lenses of quartz in the epidote aggregates. 



The contacts of the veins and the hornblende masses are also far 

 from sharp. Occasionally there is a streak of small pink garnets sepa- 

 rating the two, but for most of the distance the epidote aggregate pen- 

 etrates the hornblende mass, and hornblende grains are embedded in 

 the epidote. The hornblende mass consists mainly of large crystalloids 

 of hornblende — j^ellow-green — with large nuclei composed mainly of 

 partly amphibolized light yellowish augite. Often the partially al- 

 tered pyroxene comprises three-fourths of the area of the grain, and 

 around it is a zone of compact green-yellow hornblende with sharp 

 fibrous projections extending from the more compact portion. Ex- 

 tinctions of 24° against the cleavage in the surrounding zone and of 

 45° in the nucleus are characteristic. In the spaces between neighbor- 

 ing pieces of hornblende are small nests of quartz and calcite and often 

 in pieces of the amphibole that are not so compact are enclosures of 

 quartz and many more of calcite. Often the areas between the large 

 amphibole grains are filled with quartz and carbonate grains and 

 spicules of green hornblende, but in no case seen do the spicules 

 actually cut through the carbonate and quartz. These minerals appar- 

 ently simply fill in the spaces between the spicules. 



These fine-grained veins are believed to be small veins of pegmatite 



