After reinventing herself in the ’90s as a songwriter with soul, Emmylou Harris returned to her country roots in 2008. “No matter how bright I glitter, baby, I could never be gold,” she coos with Dolly Parton and Vince Gill on “Gold.” But there’s gold galore here, as her pure crystalline twang illuminates hidden corners of songs by Tracy Chapman and Merle Haggard. And harmonizing with the McGarrigle sisters, she makes heartbreak sound like an angelic dream on “How She Could Sing the Wildwood Flower.”