Chemical weathering takes place at or near the Earth's surface under very low temperatures and low pressures.  Those silicate minerals that form last are more in equilibrium with surface conditions and thus are less susceptible to change than those that crystallize first.  The Y diagram is a list of minerals relative to their ability to resist the changes of chemical weathering or decreasing stability as one moves up the Y diagram.

Chemical weathering changes the chemical composition of the original minerals by producing five weathering products:  Amorphous Quartz, Clay Minerals, Soluble Carbonates, Oxides of Fe and Mg and Hydroxides of Fe and Mg.  Clay Minerals are solid weathering products.  Amorphous Quartz can be solidified to form Chert Nodules, Beds of Chert or Chert Cement.  Soulble carbonates can be precipitated to form Limestone, Dolomite or various carbonate cements.  Fe Hydroxide and Fe Oxides most frequently occur as Limestone and Hematite.  The Y diagram makes the association with the minerals that produce these weathering products easy to summarize.

1. All the minerals on the Y diagram will produce Amorphous Quartz.
2. All the minerals on the Y diagram will produce clay minerals except for Quartz and Olivine.
3. All the minerals on the Y diagram except Quartz will produce soluble carbonates.  Cations such as Ca, Na, K, Fe and Mg will determine the specific carbonate that is formed.
4. All the minerals on the upper left of the Y diagram will produce oxides and hydroxides of Fe and Mg the remainder will not.