Raisaite, CuMg[Te6+O4(OH)(2)]center dot 6H(2)O, is a new mineral found at the Sentyabr'skoe deposit, Ilirney ore district, Western Chukotka, North-Eastern Region, Russia. It is associated with gypsum, malachite, azurite, cerussite, anglesite, brochantite, linarite, posnjakite, chlorargyrite, acanthite, gold, brucite, goethite, coronadite, paratellurite, and xocomecatlite in the oxidation zone of quartz veins with calcite, dolomite, ankerite, muscovite, pyrite, chalcopyrite, galena, sphalerite, hessite, petzite, altaite, primary acanthite and gold, etc. Raisaite occurs as prismatic crystals (up to 0.1 x 0.6 mm), as groups or crusts (up to 0.4 x 0.6 mm) and as dense roundish clusters (up to 0.2 mm in diameter) forming botryoidal aggregates (up to 1 mm across). Raisaite is transparent, light blue to bright sky blue, with a vitreous lustre. Its Mohs' hardness is ca. 2. Cleavage is imperfect, probably on (100), the fracture is uneven. D-meas = 2.82(1), D-calc = 2.828 g cm(-3). Raisaite is optically biaxial (+), al