Lewis & Short

1. magnes, ētis, m., = μάγνης, with or without lapis, a magnet, loadstone: (lapis), quem magneta vocant patrio de nomine Grai Magnetum quia sit patriis in finibus ortus, Lucr. 6, 908; cf. Plin. 36, 16, 25, § 126: lapis, Lucr. 6, 1046; Cic. Div. 1, 39, 86.
Without lapis, Sil. 3, 265.
Hence, adj.: magnētĭcus, a, um, magnetic: gemma, Claud. de Magnet. 26.