* Mica schist contains minerals like mica, quartz, and feldspar. Mica itself doesn't react significantly with HCl.

* Feldspar, however, will react slowly with HCl. This reaction is more pronounced with certain types of feldspar like plagioclase. The reaction produces a slight effervescence and releases some soluble salts.

* The reaction with quartz is negligible.

Therefore, the reaction of mica schist with HCl is primarily due to the feldspar content. The reaction will be more noticeable if the schist contains a significant amount of plagioclase feldspar and is finely ground.

Important note: The reaction with HCl is not a definitive test for mica schist, as other rocks can also react with the acid.