A new mineral, krasnoshteinite (Al₈ [B₂ O₄ (OH)₂ ](OH)₁₆ Cl₄·7H₂ O), was found in the Verkhnekamskoe potassium salt deposit, Perm Krai, Western Urals, Russia. It occurs as transparent colourless tabular to lamellar crystals embedded up to 0.06 × 0.25 × 0.3 mm in halite-carnallite rock and is associated with dritsite, dolomite, magnesite, quartz, baryte, kaolinite, potassic feldspar, congolite, members of the goyazite–woodhouseite series, fluorite, hematite, and anatase. D_meas = 2.11 (1) and D_calc = 2.115 g/cm³ . Krasnoshteinite is optically biaxial (+), α = 1.563 (2), β = 1.565 (2), γ = 1.574 (2), and 2V_meas = 50 (10)^◦ . The chemical composition (wt.%; by combination of electron microprobe and ICP-MS; H₂ O calculated from structure data) is: B₂ O₃ 8.15, Al₂ O₃ 46.27, SiO₂ 0.06, Cl 15.48, H₂ O_calc. 33.74, –O=Cl –3.50, totalling 100.20. The empirical formula calculated based on O + Cl = 33 apfu is (Al_7.87 Si_0.01 )_Σ7.88 [B_2.03 O₄ (OH)₂ ][(OH)_15.74 (H₂ O)_0.26 ]_Σ16 [(Cl_3.79 (OH)_0.21 ]_Σ4·7H₂ O. The mineral is monoclinic, P2₁, a = 8.73980 (19), b = 14.4129 (3), c = 11.3060 (3) Å, β = 106.665 (2)^◦, V = 1364.35 (5) ų, and Z = 2. The crystal structure of krasnoshteinite (solved using single-crystal data, R₁ = 0.0557) is unique. It is based upon corrugated layers of Al-centered octahedra connected via common vertices. BO₃ triangles and BO₂ (OH)₂ tetrahedra share a common vertex, forming insular [B₂ O₄ (OH)₂]⁴⁻ groups (this is a novel borate polyanion) which are connected with Al-centered octahedra via common vertices to form the aluminoborate pseudo-framework. The structure is microporous, zeolite-like, with a three-dimensional system of wide channels containing Cl^- anions and weakly bonded H₂ O molecules. The mineral is named in honour of the Russian mining engineer and scientist Arkadiy Evgenievich Krasnoshtein (1937–2009). The differences in crystal chemistry and properties between high-temperature and low-temperature natural Al borates are discussed.