How does jasper form?

Jasper is a form of chert with impurities and inclusions. For example, an Fe impurity will cause for the red-coloured Jasper, Cu will cause for blue, Ni for green, etc. Chert is an extremely hard, microcrystalline form of quartz. It is typically formed by the accumulation of silicious skeletons of marine creatures (e.g. diatoms and radiolarians; form in beds of chert) or by chemical replacement (i.e. migration of silica) of nodules in carbonates. Jasper is typically in association with the later, for if formation occurs as a nodule in an iron-rich dolostone, fluids that migrate the silica will also cause for the iron to relocate, causing the impurity upon precipitation.