A　new　chalcogenide　crystal,　(NH4)(4)Ag12Sn7Se22　(FJSM-STS),　has　been　solvothermally　synthesized.　The　crystal　structure,　which　is　composed　of　arrays　of　[Sn3Se9](n)(6n-)　chains　interconnecting　[SnAg6Se10](n)(10n-)　and　[Ag3Se4](n)(5n-)　layers,　is　unprecedented　among　the　reported　A/Ag/Sn/Q　(A　=　cation;　Q　=　S,　Se,　and　Te)　compounds.　Optical　absorption　together　with　theoretical　calculations　of　the　band　structure　indicate　a　direct　band　gap　of　1.21　eV　for　FJSM-STS,　which　is　close　to　the　ideal　band　gap　to　maximize　the　photoconversion　efficiency　proposed　by　Shockley　and　Queisser.　The　toxic　metal-free　crystal　of　FJSM-STS　exhibits　obvious　photosensitivity　in　the　near-infrared　range.　The　variates　of　power　and　temperature　on　the　photosensitivity　have　been　studied.