Gem Club’s haunting, melancholic music harks back to the early days of the 4AD record label and bands like This Mortal Coil, when such spare and emotionally expansive music was a rare thing. Today’s indie scene is full of pensive, gentle music, but artists as gifted as, say, Bon Iver aren’t so common. Using little more than piano, cello, and Christopher Barnes’s heartbreaking, glacial vocals, the Boston duo (with Barnes on piano and Kristen Drymala on cello) creates music that wafts by like a cloud. Resonant, solemn piano and cello notes are sustained in layers of white space accented by occasional wooden rattles or a rare percussive sparkle. Gem Club is all about mood: one built on longing, sadness, regret, and all those other pit-of-the-stomach emotions that pair so well with rainy afternoons. It’s also inarguably romantic music, and candlelight shadows would beautifully complement lyrics like “Just your touch could cure my lonesome blood” (from the stunning weeper “Twins”). Barnes’s noble husk of a voice wavers to make it to the song’s end, his two-syllable treatment of the word “mouth” itself heartrending.