Lovely Vintage Silk? The French Fact Floral Dress

gorgeous dress from the late 70s. perfect summer dress - fully lined except sleeves. delicately gathered at the neck and waist. elastic waist. belt loops but no belt. size and fabric tags are missing- feels like silk but i can't be sure. pristine condition. would best fit an S-M. approximate flat measurements: chest 18.5" waist 15" + length 42" boho floral academia cottage-core wedding festival