A boron-rich member of chlorite with an ideal chemical composition of Li_1+3xAl_4-x(BSi₃)O₁₀(OH,F)₈ where x = 0.0 to 0.33 atoms per formula unit (Zagorsky et al., 2003). Borocookeite occurs as the Ia polytype. Borocookeite has been found in miarolitic cavities at temperatures greater than 240-265^oC in pegmatite deposits, such as in the Krasny Chikoy district, Chita region, Russia.
Cf., manandonite, boromuscovite