PGM IV. 2785-2890 lists a prayer to Selene for any spell as part of a protective charm 73. A lodestone is to be used and it should have a triple faced Hekate carved upon it with the middle face having a bull horned maid, the left a dog and the right a goat 74. It was cleaned in natron and water and dipped in the blood of a person who died a violent death 75. PGM IV.2622-2707 lists the creation of a protective charm in which it is made with a magnet and an image of Hekate inscribed upon it 73 and 74.
73 Betz, H-D, ed. 1996. The Greek Magical Papyri in Translation. Chicago: University of Chicago Press.
74 Sanchez, T. 2011. The Temple of Hekate. London: Avalonia, pg 174.
75 d’Este, S. and Rankine, D. 2009. Hekate: Liminal Rites. London: Avalonia.
Note: Lodestone is also sometimes known as magnetite.
The Symbols of the Goddess Hekate