More Andesite (whinstone) that atracts a magnet

I discovered this whinstone today it has been used as a bridge in two locations over a drainage channel just south of the larchfield community, there's a 16 inch pipe under the stone so i imagine it was done in the early to mid 20th century, probably with left over mined whinstone from the Stainton area.
All the stone in the image attracted the magnet shown stuck to the whinstone block above the pipe.