Say your prayers! An ancient "cursing stone" used by Christian pilgrims to curse their enemies has just been found in the island of Canna, Scotland:
The round stone with an early Christian cross engraved on it, also known as a “bullaun” stone, is believed to be the first of its type to be found in Scotland, and was discovered by chance in an old graveyard on the island.
More commonly found in Ireland, the stones were used by ancient Christian pilgrims, who would turn them either while praying or when laying a curse, and were often to be found on sacred pilgrim routes. Traditionally, the pilgrim would turn the stone clockwise, wearing a depression or hole in a bigger “socket” stone underneath.
Defining Christianity is not a simple task. What Thomas Oden calls "consensual theology" is probably the best approach to take.
A "by the Book" method has serious limits, made plain when popular theology (that which is practiced by the adherents) is in serious conflict with creedal statements.
Using magic to hurt people doesn't sound very Christian, though.
I find no compelling evidence to believe this cross of Christian origins. The cross as a symbol is older than history. It was used by the Egyptians and formed the base of the Ankh symbol - which one may argue is the original Christian Cross.
I plowed through hundreds of different crosses Christian and otherwise and could not find any that are identical to this one. This cross is equisdistant in all directions and each arm of the cross terminates at an inverted semicircle. I found no such crosses in my searches.
A traditional Celtic/Irish cross does not look like that either. It is typically a cross with beveled edges, bowed ends and set inside of a complete circle with a lot of pretzels.