Lewis & Short

lygdĭnus, a, um, adj., = λύγδινος, of white marble: horoscopus, Jul. Val. Rer. Gest. Alex. M. 1, 3.
Esp.: lygdinus lapis, a dazzling white marble found in the island of Paros, Plin. 36, 8, 13, § 62; Isid. Orig. 16, 5, 8 (the same as lygdos).