<sec> <title>Abstract—</title> Two closely related new minerals arsmirandite Na<sub>18</sub>Cu<sub>12</sub>Fe<sup>3+</sup>O<sub>8</sub>(AsO<sub>4</sub>)<sub>8</sub>Cl<sub>5</sub> and lehmannite Na<sub>18</sub>Cu<sub>12</sub>Ti<sup>4+</sup>O<sub>8</sub>(AsO<sub>4</sub>)<sub>8</sub>FCl<sub>5</sub> were discovered in sublimates of the Arsenatnaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. They are associated with one another and with hematite, sanidine, sylvite, halite, tenorite, cassiterite, rutile, and various arsenates and sulfates. Arsmirandite and lehmannite are visually indistinguishable and occur as equant crystals up to 20 × 20 × 30 μm<sup>3</sup>, typically combined in thin crusts up to 2 × 3 cm. The minerals are dark greyish green to olive-greenish black and have strong vitreous lustre. D<sub>calc</sub> = 3.715 (arsmirandite) and 3.676 (lehmannite) g cm<sup>–3</sup>. The empirical formula of arsmirandite
