UNITED STATES MINERAL RESOURCES 



RARE-EARTH ELEMENTS 



By John W. Adams and Mortimer H. Staatz 



CONTENTS 



Abstract of conclusions 547 



Introduction 547 



Uses 548 



Availability 548 



Geologic environment 549 



Geochemistry 549 



Mineralogy 550 



Types of deposits 551 



Resources 552 



Present situation 552 



Potential resources 552 



Prospecting techniques 554 



Problems for research 554 



Selected references 555 



FIGURE 



Graph showing crustal abundance of rare-earth 

 elements 



TABLES 



115. Rare-earth content of various rock types 549 



116. A partial listing of rare-earth-bearing minerals 550 



117. Identified sources of the rare earths and some 



potential rare-earth deposits of the world 553 



ABSTRACT OF CONCLUSIONS 



The rare-earth metals, which include yttrium and the 

 lanthanides, consist of a group of geochemically related ele- 

 ments that have become of increasing economic interest, 

 largely on the basis of their physical rather than their 

 chemical properties. Their greatest present use is in petro- 

 leum-cracking catalysts, but they are also extensively used 

 in the glass and ceramics industries, in iron and steel pro- 

 duction, and in the manufacture of electronic devices. 



Some members of the group are relatively abundant in 

 the earth's crust, but minable concentrations are uncommon. 

 Bastnaesite, a rare-earth fluocarbonate, and monazite, a 

 rare-earth phosphate, are the two important ore minerals. 

 Bastnaesite is mined extensively from carbonatite in Cali- 

 fornia, and monazite is recovered largely from placer de- 

 posits in various parts of the world. The rare earths are 

 present in many other minerals, either as essential con- 

 stituents or as substituted constituents. Apatite is a com- 

 mon host of the substituted constituents and is a source of 

 rare earths as a byproduct of fertilizer manufacture in 

 Europe. 



The large reserves of bastnaesite in California make the 

 United States self-sufficient in the lanthanide elements, but 

 no such high-grade source of yttrium is known. Potential 

 domestic resources capable of meeting projected require- 

 ments, however, are available. 



INTRODUCTION 



The rare-earth group of metals, also called the 

 lanthanide elements, comprises 15 elements having 

 atomic numbers 57 through 71. These are lanthanum 

 (La), cerium (Ce), praseodymium (Pr), neodym- 

 ium (Nd), promethium (Pm), samarium (Sm), 

 europium (Eu), gadolinium (Gd), terbium (Tb), 

 dysprosium (Dy), holmium (Ho), erbium (Er), 

 thulium (Tm), ytterbium (Yb), and lutetium (Lu). 

 One of these, promethium, is best known as an arti- 

 ficially produced element, although its occurrence 

 in minute trace amounts in natural materials has 

 been reported. In addition to the lanthanides, yt- 

 trium (Y), with atomic number 39, is generally 

 classed with the rare earths because of its chemical 

 similarities and geochemical affinities. The rare- 

 earth group is divided into the cerium subgroup, or 

 "light" rare earths, which consists of the first seven 

 lanthanide elements listed (lanthanum through 

 europium), and the yttrium subgroup, or "heavy" 

 rare earths, which consists of yttrium and the last 

 eight lanthanide elements listed (gadolinium through 

 lutetium). 



U.S. GEOL. SURVEY PROF. PAPER 820 



547 



