It was found that a pinkish and weathered stone in the stock of the petalite from Africa was composed of cookeite and quartz. Some mineralogical characteristics of the cookeite after refining were investigated.
The structure formula of this cookeite induced from chemical composition is (Al_1.991 Fe_0.009)(OH) ₂ (Al_0.584 Si_3.416) O₁₀^0.584- (Li_1.118 K_0.036 Na_0.171 Mg_0.014 Ca_0.063 Mn_0.005 Al_1.698)(OH) ₆^0.583+. The basal spacing is 14.16Å, and does not change by the treatments with 6N-HCI, 1N-NH₄NO₃, potassium acetate, and ethylene glycol. The intensity of the reflection of (001) become maximum by heat treatment at 500°C. Only β-spodumen and mullite appear when heated at 1300°C.