Feldspar is a minor component of clay, and
its content is generally very low in our samples (~2–8%), which contain
both alkali feldspars (orthoclase and microcline) and plagioclase feldspars.
Gypsum is very rare, and was detected in only two samples in
low (~3%, AR1) or significant (~35%, AR2) amounts. One sample
(AR9) also contains cristobalite (~6%).