Nature has exhibited changes in its chemical composition in space and time, and the study of this change give us the opportunity to understand chemical processes and their outcomes. After the selecting a test medium (bedrock, rock debris, etc.), or several in parallel, two or three properties could be measured, perhaps even over time, in order to quantify change. The goal of a particular investigation will determine what type of sample material will be chosen.
- Bedrock –This is the standard and original geochemical sample medium, prone to being inhomogeneous so often a large number of samples will be required to achieve reliable results.
- Mineral Soil –A term use for a wide variety of rock debris that has not been the transported by water, and includes various types of moraine, weathered material, landslide material, etc..
- Stream sediments – These are the products of erosion, transport and break down of debris, which have originated from various eroded areas upstream in relation to the "discovery site".
- Flood sediments –In flood situations, debris erodes away from many areas in the catchment area, and the flood water shows a higher concentration of suspended material, like sediments, as water speed slows downs.
- Vegetation–Through root intake, precipitation and mineral particle/dust in the air, vegetation develops its own chemical composition, but from time to time this can greatly vary from plant species to another.
- Water –The chemical composition of a water sample is effected by how it was formed, and the contact its has had with vegetation, debris and bedrock as it flows as surface water or as leachate down to the ground water, and on to the sea, to eventually evaporate again.
- Agricultural soil– Most often this is, more or less, a mechanically/chemically modified debris found near its place of origin.