Issued by the Soviet Union in 1966, this 6-kopeck commemorative stamp celebrates the VII International Congress of Crystallographers held in Moscow. The design features the IUC (International Union of Crystallography) emblem formed with alternating blue and black triangles, symbolizing crystal symmetry. Flanking the emblem are stylized crystal structures rendered in brown tones, highlighting the scientific theme. A clean bilingual inscription “МОСКВА / MOSCOW” marks the host city. A highly sought-after issue for thematic collectors of science, chemistry, and Soviet academic commemoratives.