Lopatkaite, ideally Pb₁₀As₂Sb₆S₂₂ (Z = 4), is a new arsenic-bearing sulfosalt species found in the Madoc deposit, Taylor Pit, Ontario, Canada. Associated minerals in the holotype specimen are boulangerite, veenite, and sterryite, all embedded in a calcite matrix. The ideal formula may be derived from the ideal boulangerite formula, Pb₁₀Sb₈S₂₂ (Z = 4), by a substitution of 2Sb with 2As. Lopatkaite is a homeotype of boulangerite and a new member of the rod-based family of sulfosalts.