Boji stones are primarily a composite of pyrite with palladium. They are found in two different shapes: round smooth ones, which are said to be "female" and rougher / spiky ones, which are said to be "male". Some stones - notably the "Rainbow Bojis" carry both male and female aspects combined in one stone and so you need just one of these instead of a pair. Having said that, I have used 7 rainbow bojis (one to each major chakra) to great effect! The rainbow bojis also show distinct colouring in metallic lustres of green, gold, blue, orange and purple, and are quite amazing (and hard to find!). Some of the "normal" bojis may also display some colour - in fact some of the ones for sale have a golden sheen to parts of them. We feel that Bojis are the best balancing stone you can buy: the inherent polarity and balance in their nature is what makes them so important to the metaphysician and healer, along with a phenomenal ability to earth and ground. We always take "normal" bojis with us when teaching workshops, as we defy anyone feeling spacey NOT be grounded properly by these little wonders. Please do not be misled by confusing Mochi Balls/marbles with Bojis - they are NOT the same energy. All bona fide Bojis should also come with a certificate of authenticity. Please also note that they should NOT be struck together (!) and are best stored not touching each other.