Besides resistant relic minerals of the parent rock, saprolites contain predominantly quartz and a high percentage of kaolinite with other clay minerals which are formed by chemical decomposition of primary minerals, mainly feldspars. More intense weathering conditions, exceeding the saprolite stage, give rise to a continuous transition to laterite soils.
The saprolite is divided into three main zones; the upper saprolite, lower saprolite and saprock.
The upper saprolite is chemically oxidised to the point where few reduced chemical species exist. For instance, iron is present as Fe3+, sulfur is present predominately as sulfates, manganese is present as manganese oxide, silicates are present as clays.
The upper saprolite zone may exist down to 300 metres below surface in extreme cases, and throughout large regions of the tropics, may exceed 50 metres. Within the ancient regolith of the Yilgarn Craton, saprolite typically exceeds 100m depth.
The lower saprolite sees an oxidation front between chemically oxidised minerals and chemicals above, and chemically reduced minerals and chemicals existing below. This manifests as a change from Fe3+ which lends the red or orange suite of colors to the upper saprolite, to Fe2+ which tends to colour the rock mass green or green-brown.
The oxidation front is a prime marker and an important horizon for ore deposits, especially uranium deposits. The oxidation front and change from upper to lower saprolite sees a change in redox potential and ionic state of most metals, which may prompt downward-travelling oxidised species to leave solution.
The oxidation front is also the point at which sulfur is reduced enough to exist in a sulfide form and hence, there is typically some form of supergene enrichment in metal sulfide minerals. This is an important zone in many ore deposits and an integral part of the ore genesis of Manto ore deposits.
The top of fresh rock, typically, is taken as the point at which no further visible weathering is evident. However, chemically it is usually able to be shown that weathering and oxidation effects may persist a considerable distance into the Earth's crust, especially around large fault systems.
It is also worth noting that in many hydrothermal fields, weathering and oxidation of the rocks is enhanced by the hydrothermal waters, giving rise to an alteration zone of metasomatic origin. It is arguable whether or not this counts as saprolite.
Saprolite destruction occurs via physical erosion, predominantly via water movement across the surface. However, in eolian dune systems and arid wind-prone deserts scouring of the land surface via wind-blown particles is an important mechanism for removal of saprolite. Within the ice deserts and some periglacial uplands, wind and freeze-thaw may also remove saprolite.
Saprolite is generally not formed in glacial environments as glaciation removes all soft, weathered material readily. It is for this reason that the majority of the Canadian Shield and the Siberian Craton are devoid of significant saprolite.
The white clay mottles or 'megamottles' tend to form vertically arrayed tubular conduits of bleached white kaolinite within a hematite-rich clay matrix. In a widely recognised and growing number of sites there have been found fossilised tree roots.