The new mineral evseevite was found in the Arsenatnaya fumarole, Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. Evseevite is represented by two chemical varieties. The variety close to the end-member Na2Mg(AsO4)F (holotype) is associated with sanidine, hematite, tenorite, aegirine, cassiterite, sylvite, halite, johillerite, badalovite, calciojohillerite, hatertite, arsmirandite, yurmarinite, axelite, polyarsite, aphthitalite, potassic-magnesio-fluoro-arfvedsonite, litidionite, ferrisanidine and tridymite. The P- and S-enriched variety (cotype) is associated with hematite, fluorophlogopite, svabite, fluorapatite, tilasite, calciojohillerite, forsterite, cassiterite, belomarinaite and aphthitalite. Evseevite occurs as prismatic, acicular or hair-like crystals up to 0.7 mm long combined in clusters up to 0.5 mm, brushes or crusts up to 2 × 2 mm. It is transparent, colourless or pale pinkish, with vitreous lustre. Dcalc is 3.377 g cm–3 for the holotype and 3.226 g cm–3 for the cotype. Evseevite is optically uniaxial (+), α = 1.545(2), β = 1.546(2), γ = 1.549(2) and 2Vmeas = 40(10)°. The empirical formulae calculated based on O+F = 5 apfu are (Na1.99Ca0.03K0.01)Σ2.03(Mg0.98Fe3+0.01Zn0.01Cu0.01)Σ1.01[(As0.98Si0.01)Σ1.01O4](F0.97O0.03) for the holotype and Na2.02(Mg1.00Fe3+0.03)Σ1.03[(As0.69P0.25S0.07)Σ1.01O4](F0.78O0.22) for the cotype. Evseevite is orthorhombic, Pbcn, a = 5.3224(1), b = 14.1255(3), c = 12.0047(3) Å, V = 902.53(4) Å3 and Z = 8. Strong reflections of the powder XRD pattern [d,Å(I)(hkl)] are: 4.001(100)(121), 3.479(56)(023), 3.041(45)(042), 2.657(44)(200), 2.642(68)(142) and 2.613(36)(104). The crystal structure was solved from single-crystal XRD data and refined on powder data by the Rietveld method, Rwp = 0.0068, Rp = 0.0047 and Robs = 0.0435. Evseevite is isostructural to moraskoite Na2Mg(PO4)F. The structure of evseevite can be described in terms of anion-centred polyhedra. F-centred octahedra [FNa4Mg2]7+ share faces to form chains [FNa2Mg]3+ and AsO4 tetrahedra are located between the chains. Evseevite belongs to a small set of minerals with antiperovskite structures and is the first natural arsenate with antiperovskite units. The mineral is named in honour of the Russian mineralogist Aleksandr Andreevich Evseev (born 1949).

新矿物伊夫塞维特是在俄罗斯堪察加半岛托尔巴奇克火山托尔巴奇克大裂缝喷发北部突破的第二火山渣锥Arsenatnaya喷气孔中发现的。 Evseevite 有两个化学品种。接近端元Na 2 Mg(AsO 4 )F（正模）的品种与钠铁矿、赤铁矿、长铁矿、白铁矿、锡石、钾盐、岩盐、镁铝矿、巴达洛铁矿、钙铁矿、钙铁矿、砷铁矿、玉铁矿、轴石、聚芳石、辉石、钾镁氟石、锂二沸石、铁硅石和鳞石英。富含 P 和 S 的品种（共型）与赤铁矿、氟金云母、斯瓦比特石、氟磷灰石、钛硅铁矿、钙镁橄榄石、镁橄榄石、锡石、白云石和硬铅矿有关。叶夫塞维石呈棱柱状、针状或毛发状晶体，长度可达 0.7 毫米，簇状可达 0.5 毫米，刷状或结壳可达 2 × 2 毫米。透明、无色或淡粉色，有玻璃光泽。正模的 D计算值为 3.377 g cm –3 ，副模的 D 计算值为3.226 g cm –3 。 Evseevite 是光学单轴 (+)、α = 1.545(2)、β = 1.546(2)、γ = 1.549(2) 和 2V meas = 40(10)°。根据O+F = 5 apfu计算的经验公式为 (Na 1.99 Ca 0.03 K 0.01 ) Σ2.03 (Mg 0.98 Fe 3+ 0.01 Zn 0.01 Cu 0.01 ) Σ1.01 [(As 0.98 Si 0.01 ) Σ1.01 O 4 ](F 0.97 O 0.03 ) 为正型，Na 2.02 (Mg 1.00 Fe 3+ 0.03 ) Σ1.03 [(As 0.69 P 0.25 S 0.07 ) Σ1.01 O 4 ](F 0.78 O 0.22 ) 为副型。 Evseevite 是斜方晶系，Pbcn，a = 5.3224(1)，b = 14.1255(3)，c = 12.0047(3) Å，V = 902.53(4) Å 3和Z = 8。粉末 XRD 图案的强反射 [ d ,Å( I )( hkl )]为：4.001(100)(121)、3.479(56)(023)、3.041(45)(042)、2.657(44)(200)、2.642(68)(142)和2.613(36)(104)。晶体结构通过单晶 XRD 数据求解，并通过 Rietveld 方法对粉末数据进行精修，R wp= 0.0068，R p = 0.0047，R obs = 0.0435。 Evseevite 与 Morakoite Na 2 Mg(PO 4 )F 具有同构结构。 evseevite 的结构可以用阴离子中心多面体来描述。 F中心八面体[FNa 4 Mg 2 ] 7+共用面形成链，[FNa 2 Mg] 3+和AsO 4四面体位于链之间。 Evseevite属于一小类具有反钙钛矿结构的矿物，是第一个具有反钙钛矿单元的天然砷酸盐。该矿物以俄罗斯矿物学家 Aleksandr Andreevich Evseev（生于 1949 年）的名字命名。