Surface　hydroxyl　group　exchange　has　been　identified　as　one　of　primary　factors　in　the　fluoride　adsorption　process.　So　far,　the　construction　of　surface　oxygen　defects　for　producing　more　surface　hydroxyl-OH　is　mainy　involved　in　high-temperature　procedures　under　vacuum　or　hydrogen　atmosphere,　or　high-pressure　processes　such　as　hydrothermal　and　solvothermal　techniques,　thus　necessitating　the　development　of　effective　methods　for　practical　applications.　In　this　study,　anorthite　(CaAl2Si2O8,　abbr.　An)　with　abundant　surface　oxygen　vacancies　(Ov)　is　facilely　synthesized　through　CO2　weathering　decalcification　chemistry.　The　process　is　one　of　the　main　degradation　mechanisms　of　natural　alkaline　silicate　minerals,　and　involves　a　simple　chemical　reaction　between　alkaline　CaO　and　CO2　present　in　the　atmosphere.　More　Ov　appearing　on　the　resultant　calcium-deficient　anorthite　(abbr.　de-Ca　An)　increases　surface-OH　content,　which　is　verified　by　first-principles　calculations　and　abundant　spectrum　analyses.　It　is　found　that　de-Ca　An　adsorbent　shows　better　adsorption　performance　towards　fluoride　in　the　solution　phase.　Typically,　after　adsorption　equilibrium　the　removal　efficiency　reaches　98.4　%　(60　mg　An)　and　99.3　%　(60　mg　de-Ca　An)　with　the　fluoride　concentration　of　15　mg/L　(60　mL,　pH　=　3).　At　the　preferred　pH　=　3,　the　saturated　adsorption　capacity　of　de-Ca　An　is　82.5　mg/g,　which　is　greatly　improved　compared　with　An　sample　(63.8　mg/g).　Surface-OH　ligand　exchange　on　de-Ca　An　plays　a　important　role　in　the　efficient　adsorption　of　fluoride.　In　addition,　the　effects　of　pH,　surface　potential,　fluoride　concentration,　and　co-existing　anions　are　also　discussed　extensively　to　prefer　adsorption　conditions　for　optimum　defluoridation　performance.　The　judicious　chemical　composition　and　defect　engineering　collaboratively　enhance　the　effective　removal　of　fluoride　using　the　de-Ca　An　adsorbent,　thus　exhibiting　significant　potential　for　cleaning　fluoride-containing　water.