Sb-rich avicennite (first discovery in Russia) was found at the Khokhoy gold deposit, 120 km west of Aldan, Aldan district, Republic of Sakha (Yakutia), Eastern Siberia, Russia. The mineral of critical metal thallium forms irregularly shaped grains up to 0.25 mm in size, in association with amgaite, weissbergite, goethite, gold, and unidentified Tl-bearing phases. Aggregates of colloform structure prevail, represented by rhythmic-, concentric-zonal, kidney-shaped, and spherulitic varieties. Avicennite is black in color, with metallic luster, and it fractures unevenly. No cleavage is observed. The density value of avicennite, obtained using its empirical formula and the unit cell parameters calculated from the powder X-ray diffraction data, is 8.548 g/cm3. In reflected light, avicennite is light gray and isotropic. Internal reflections are absent. Reflection is very low; the reflectivity curve is of mixed type with a small maximum in the blue part. Its chemical composition (average value on 10 analyses, wt.%): Tl2O3—85.36, V2O5—0.73, As2O5—0.85, Sb2O5—12.98, Total—99.92; It corresponds to the following empirical formula (calculation for three atoms of O): Tl1.40Sb5+0.30V5+0.03As5+0.03O3. The unit cell parameters calculated from the powder X-ray diffraction data are as follows: the mineral is cubic, a = 10.496(6) Å, V = 1156(2) Å3.