POLYMICT UREILITES ARE BRECCIAS REPRESENTING REGOLITH DEVELOPED ON AND NEAR THE SURFACE OF A UREILITIC ASTEROID. THEY CONSIST MOSTLY OF CLASTS THAT ARE INDISTINGUISHABLE FROM MAIN GROUP UREILITES. HOWEVER THEY ALSO CONTAIN SEVERAL OTHER TYPES OF CLASTS WHICH PROVIDE A WEALTH OF INFORMATION NOT AVAILABLE IN MAIN GROUP UREILITES AND CAN BE USED TO ADDRESS MAJOR UNRESOLVED PROBLEMS IN UREILITE HISTORY. THESE INCLUDE 1) FELDSPATHIC CLASTS THAT MAY REPRESENT CRUSTAL IGNEOUS ROCKS FROM THE UREILITE PARENT BODY; 2) CARBONACEOUS CHONDRITE-LIKE (DARK) CLASTS THAT MAY REPRESENT UREILITE PRECURSOR MATERIALS; AND 3) FOREIGN CLASTS THAT PROVIDE INFORMATION ABOUT THE SOLAR SYSTEM ENVIRONMENT IN WHICH THE UREILITE PARENT BODY EVOLVED. WE WILL STUDY THESE MINOR CLAST POPULATIONS WITH THE FOLLOWING OBJECTIVES: OBJECTIVE 1: TO DETERMINE THE PETROLOGIC AND CHEMICAL PROPERTIES OF ALL INDIGENOUS IGNEOUS LITHOLOGIES IN POLYMICT UREILITES AND DETERMINE THE RELATIONSHIP OF EACH LITHOLOGY TO MAIN GROUP UREILITES IN ORDER TO UNDERSTAND THE IGNEOUS EVOLUTION OF THE UREILITE PARENT BODY. OBJECTIVE 2: TO CHARACTERIZE THE MINERALOGY AND PETROLOGY OXYGEN AND CHROMIUM ISOTOPES AND AR-AR AGES OF CARBONACEOUS CHONDRITELIKE CLASTS IN POLYMICT UREILITES IN ORDER TO DETERMINE WHETHER THEY REPRESENT UREILITE PRECURSOR MATERIALS OR ARE FOREIGN. OBJECTIVE 3: TO CHARACTERIZE THE MINERALOGY PETROLOGY AND OXYGEN ISOTOPES OF ALL FOREIGN CLASTS IN POLYMICT UREILITES FOR COMPARISON WITH KNOWN METEORITE TYPES IN ORDER TO PROVIDE INFORMATION ON THE SOLAR SYSTEM ENVIRONMENT(S) IN WHICH THE UREILITE PARENT BODY ACCRETED AND EVOLVED. THE OVERARCHING OBJECTIVE OF THE PROPOSED WORK IS TO TAP THE INFORMATION AVAILABLE IN POLYMICT UREILITES TO ADDRESS MAJOR QUESTIONS ABOUT UREILITE HISTORY. RESULTS WILL PROVIDE NEW INSIGHTS INTO THE CHEMICAL AND ISOTOPIC COMPOSITIONS OF THE EARLIEST SOLAR SYSTEM MATERIALS AND THE DIVERSITY OF DIFFERENTIATION PATHS AMONG SOLAR SYTEM BODIES. THE PROPOSED WORK BUILDS ON EXTENSIVE EXPERIENCE OF THE PI AND COLLABORATORS IN STUDYING PRIMITIVE METEORITES THROUGH NASA-FUNDED RESEARCH PROGRAMS. IT FOCUSES ON MAJOR PROCESSES AFFECTING PLANETESIMALS IN THE FIRST FEW MILLION YEARS OF SOLAR SYSTEM HISTORY AND THEREFORE IS DIRECTLY RELEVANT TO THE GOAL OF THE EMERGING WORLDS PROGRAM TO UNDERSTAND "THE FORMATION AND EARLY EVOLUTION OF THE SOLAR SYSTEM (ROSES 2016 APPENDIX C.2).