The new zeolite - dachiardite-K (IMA No. 2015-041) - the K-dominant member of the dachiardite series with the idealized formula (K ₂ Ca)(Al ₄ Si ₂₀ O ₄₈ )∙13H ₂ O, has been found in salbands of opal-chalcedony hydrothermal veinlets cross-cutting hydrothermally altered effusive rocks of the Zvezdel paleovolcanic complex near the village of Austa, Momchilgrad Municipality, Eastern Rhodopes, Bulgaria. It occurs there in association with chalcedony, opal, dachiardite-Ca, dachiardite-Na, ferrierite-Mg, ferrierite-K, clinoptilolite-Ca, clinoptilolite-K, mordenite, smectite, celadonite, calcite, and barite. Dachiardite-K forms spherical radial aggregates, up to 8 mm in diameter, consisting of split needle-shaped individuals. Color is white to colorless. Perfect cleavage is observed on (100). D _meas = 2.18(2), D _calc = 2.169 g/cm ³ . The IR spectrum is given. Dachiardite-K is biaxial (+), a = 1.477 (calc.), b = 1.478(2), g = 1.481(2), 2V _meas = 65(10)°. The chemical composition (electron microprobe, mean of 6 spot analyses, H ₂ O determined by thermogravimetric method, wt %) is: K ₂ O 4.51, CaO 3.27, BaO 0.41, A1 ₂ O ₃ 10.36, SiO ₂ 67.90, H ₂ O 13.2, total 99.65. The empirical formula is: H _26.23 K _1.71 Ca _1.04 Ba _0.05 Al _3.64 Si _20.24 O ₆₁ . The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 9.76 (24) (001), 8.85 (58) (200), 4.870 (59) (002), 3.807 (16) (202), 3.768 (20) (112, 020), 3.457 (100) (220), 2.966 (17) (602). Dachiardite-K is monoclinic, space group C2/m, Cm or C2; unit-cell parameters refined from powder data are: a = 18.670(8), b = 7.511(3), c = = 10.231(4) Å, b = 107.79(3)°, V= 1366(1) Å ³ , Z = 1. The type specimen is deposited in the Earth and Man National Museum, Sofia, Bulgaria, with the registration number 23927.