This in turn limits the direction of re-radiation of light, causing the light to be reflected. An interesting result of this process is that reflected light is strongly polarised. This is utilised by drivers who wear polarised sunglasses to cut down the reflected glare of the road. Try looking at a mirror though polarised specs yourself and see if you can cut out the 'glare'. As with transmission, reflection is dependent on the wavelength of the radiation.
Metals are, in fact, transparent to higher frequencies such as X-rays.
For a start, stone is not actually as opaque as your average church wall suggests. Typically, if you cut a very thin sliver of rock you can see light through it. This is because stone is made from mineral crystals which are in themselves transparent, but are randomly packed together with irregular boundaries. The light is scattered, reflected and refracted, by these many boundaries and thus the light never penetrates very far and the stone appears opaque. So there you go.