details are given of the techniques used in the analysis of asbestiform fibers in the water systems of duluth , minnesota and other cities . 
 photographic electron diffraction and electron microprobe analyses indicated that the concentration of verified amphibole mineral fibers ranged from 20  106 to 75  106 fibers / l . 
 approximately 5060% of the fibers were in the cummingtonite - grunerite series and 20% were in the actinolite - tremolite series . 
 about 5% were chemically identical with amosite . 
 a wide variety of analytical techniques must be employed for unique identification of the mineral species present in water systems . 
 imagesfigure 1.figure 2.figure 3.figure 4.figure 5.figure 6 .