Mica-made member, electrochemical reaction unit, and electrochemical reaction cell stack

An electrochemical reaction cell stack comprising a plurality of electrochemical reaction units arrayed in a first direction,

• wherein at least one of the electrochemical reaction units is an electrochemical reaction unit,
• the electrochemical reaction unit includes:
• a unit cell including an electrolyte layer, and a cathode and an anode that face each other in a first direction with the electrolyte layer intervening therebetween;
• and
• a structural member that faces a cathode chamber facing the cathode or an anode chamber facing the anode,
• wherein the structural member is formed of a mica-made member that has been subjected to a heat treatment of 1,000° C. or higher for four or more hours so as to exhibit an intensity peak of KMg3(Si3Al)O10(OH)2 and an intensity peak of Mg2SiO4 in X-ray diffractometry (XRD), prior to assembling the structural member into the electrochemical reaction unit.