Equipment- 

 Many specialized types of equipment have been designed for heavy-mineral 

 separation procedures. The simplest and most practical setup, which is shown 

 in Figure 6-4, consists of two glass funnels, a stand to support the funnels one 

 above the other, a short rubber tube attached to the stem of the upper funnel, 

 and a tubing pinch clamp. A heavy liquid, filter paper, several beakers, a large 

 cover glass, a glass stirring rod, alcohol, and an alcohol wash bottle complete 

 the essential equipment. Petrographic glass slides, cover glasses, hot plate, 

 xylene, and mounting material (Canada balsam or Lakeside No. 70) are used 

 to prepare the mineral grains for study. 



Procedure 



The sample must first be disaggregated to free the heavy-mineral grains. 

 The author prefers to run a size analysis and then to separate the heavy minerals 

 from various size fractions. The fine- or very fine-grained sand fractions, as well 

 as the most abundant size fractions are used. The finer sized fractions are pre- 

 ferred because there is normally a higher percentage of heavy minerals in these 

 fractions, and minerals of this size can be identified petrographically more easily. 

 Larger grains often are difficult to examine under the microscope because they are 

 too thick to transmit adequate light; therefore the optical properties are difficult 

 to determine. The tendency of the silt-size particles to coagulate into small ag- 

 gregates in the heavy liquid makes it difficult to separate the heavy minerals 

 from the light fractions. The time required for small grains to settle through the 

 heavy liquid increases the time necessary for separation. Centrifuging the silt- 

 size particles will speed up the separating process. 



If a size analysis is not desired, the sample first must be disaggregated as 

 outlined under Size Analyses (see page 95). A more complete discussion of 

 sample disaggregation is given by Krumbein and Pettijohn (1938). The 

 use of acids and other chemicals should be minimized in the disaggrega- 

 tion processes because the less stable minerals may be corroded or destroyed. 

 Sand grains often are coated with iron oxide, which must be removed before 

 mineral identification. Leith (1950) discusses various reagents for removing 

 this coating from mineral grains. An ultra-sonic cleaner has been used effectively 

 to clean grains. Because no chemicals are used in this technique, there is little 

 danger of destroying or modifying the mineral grains. 



After the sample has been disaggregrated and the iron oxide eliminated, the 

 sample is dried and passed through an 80- or 115-mesh screen to remove the 

 coarse material. The silt and clay particles are removed by screening or de- 

 canting, and then the sample is dried and weighed. For most sands a 20- to 50- 

 gram sample is sufficient; however, if the percentage of heavy minerals is ex- 

 cessively low, it may be necessary to use a larger sample and to concentrate it 



104 



