Abstract: This paper presents the results of mineralogical and crystallographic studies in the first Russian finding of a mineral belonging to the fluoride class, viz., knasibfite, which was found in fumarolic deposits discharged during the Great Tolbachik Fissure Eruption. We investigated its crystal structure to corroborate the fact that knasibfite is orthorhombic, sp. gr. Imm2; a = 17.181 (2), b = 5.537 (4), c = 9.205 (7) Å, V = 875 (1) ų. The structural features that can be seen in this mineral classify it as belonging to a special group of compounds that has inherited its structure from a high temperature modification or from the medium where it crystallized.