ROCK SPECIMENS AND ORES 



113 



indicate on the labels their relative relationships and distribution. 

 Often this is most conveniently done by means of a sketch. 

 Always break specimens from the parent ledge, and not from 

 the loose material nearby, unless you are certain that this was 

 derived from the main ledge and is typical of it. 

 Do not collect specimens 



unless you know they are in 

 place at the locality. Some- 

 times large boulders have 

 been carried great distances 

 from their true geological po- 

 sitions. 



If weathered material is 

 abundant and looks interest- 

 ing, collect separate samples 

 of this, but be certain to in- 

 dicate on the label the rela- 

 tionship of this to the fresh 

 rock. 



Look for veins and dikes in 

 rocks, contacts where bedded 

 rocks are placed against crys- 

 talline, igneous formations, or 

 where two different kinds of 

 igneous rocks have a common contact. Unusual minerals often 

 occur along such contacts. When large outcrops of ore minerals 

 are found, collect several specimens at different places in order 

 to have a good, representative sampling of the outcrop, and get 

 one or more specimens of the rock which encloses the ore body. 



Fig. 66. — Shaping a rock sample. 



