Lewis & Short

sĕlēnītis, ĭdis, f., or sĕlēnītes, ae, m., = σεληνῖτις, crystalline gypsum, selenite. Form selenitis, Plin. 37, 10, 67, § 181; form selenites, Sol. 37, 31; Aug. Civ. Dei, 21, 5; Isid. 16, 4, 6.