RADON AND MINERAL CONTENT OF SOILS 185 
The following table taken from Gockel will indicate some of the 
heavy minerals associated with radioactivity. 
TABLE I 
Radium per Gram of 
Mineral Location Mineral X 10 Grams 
Zircon Kimberley 19-1 
Eudalite Greenland 12.6 
Orthite Sweden 236.0 
Gadolinite Hitter6 156.0 
Keilhanite Alve, Norway 452.0 
Niobite Connecticut 97-0 
Apatite Canada 14.6 
Cerite Sweden 30.0 
The average radium content of sedimentary rocks is about 1.4 X10” 
grams! per gram of rock. Thus it is seen how considerably the radio- 
activity is concentrated in the heavy mineral constituents. 
Petrographic examination of the heavy mineral residues from the 
South Liberty dome revealed the presence of zircon, rutile, brookite, 
tourmaline, magnetite, ilmenite, apatite, biotite, augite, and cyanite. 
Zircon, tourmaline, and magnetite are the most abundant in all the 
samples examined. If the radioactivity of the soil could be ascribed 
to the mineral composition of the soil itself rather than to any deep- 
seated source, zircon is the one mineral of all those observed that is 
the most likely to be radioactive. F. L. Hess’ describes a considerable 
number of unusual rare-earth minerals occurring in some of the 
igneous rocks of the central mineral region of Texas. Since this area 
was probably the source of much of the material of the late Gulf Coast 
Tertiary, these minerals were undoubtedly present to some extent 
in the soils but not recognized in the heavy mineral residues examined. 
In these minerals are such rare-earth elements as thorium and ura- 
nium. Thorium is the parent of one series of radioactive substances and 
uranium is the parent of the radium series and probably also of the 
actinium series. Since these elements (uranium and thorium) are 
isomorphous with zirconium, it is only logical to look for a possible 
relationship between the radon content of the’ soil and the amount 
of zircon and other rare-earth minerals in the soil. Experimentally, 
only the total heavy mineral content of the soil was determined, since 
zircon was always present in large percentages in the residues and not 
all the possible sources of radioactivity could be differentiated and 
segregated. 
1 G. Kirsch, Geologie und Radioaktivitat (Berlin, 1928), p. 46. 
2 “Minerals of the Rare-Earth Metals at Baringer Hill, Llano County, Texas.” 
US. Geol. Survey Bull. 340 (1907), pp. 286-94. 
515 
