THE OVEREACHING GOAL OF OUR RESEARCH IS TO UNDERSTAND THE HISTORY OF WATER ON THE SURFACE OF MARS THROUGH THE STUDY OF MINERALS THAT FORM FROM WATER-ROCK INTERACTIONS. PHYLLOSILICATES RESULT FROM AQUEOUS ALTERATION AND ARE PREVALENT IN THE MOST ANCIENT MARTIAN TERRAINS. THE TYPES OF PHYLLOSILICATES ON THE SURFACE AND THEIR COMPOSITIONS CAN ELUCIDATE AQUEOUS PROCESSES THAT WERE IN EFFECT DURING THE VERY DISTANT PAST ON MARS. SMECTITES ARE THE MOST COMMON TYPE OF PHYLLOSILICATE ON MARS AND ORBITAL VIS/NIR DATA AND IN SITU X-RAY DIFFRANCTION DATA FROM GALE CRATER SUGGEST THAT SOME SCEMECTITES MAY HAVE EXPERIENCED DIAGENESIS AFTER THEIR INITIAL FORMATION TO BECOME PARTIALLY CHLORITIZED. THE OBJECTIVES OF THE PROPOSED RESEARCH ARE: 1) SYNTHESIZE PARTIALLY CHLORITIZED SMECTITES WITH A RANGE OF COMPOSITIONS AND DEGREES OF CHLORITIZATION 2) CHARACTERIZE PARTIALLY CHLORITIZED SMECTITES USING INSTRUMENTS SIMILAR TO THOSE ON ORBITAL AND IN-SITU MARTIAN MISSIONS AND 3) EVALUATE THE PREVALENCE OF PARTIALLY CHLORITIZED SMECTITES WITHIN GALE CRATER AND OTHER ANCIENT MARTIAN TERRAINS TO INTERPRET THEIR DIAGENETIC ENVIRONMENTS.