Hezuolinite, (Sr,REE) _4Zr(Ti,Fe ~(3+),Fe ~(2+)) _2Ti _2O _8(Si _2O _7)2, a new mineral species of the chevkinite group from Saima alkaline complex, Liaoning Province, NE China

摘要

Hezuolinite is a new mineral species occurring as an accessory mineral in the Saima alkaline complex in Liaoning Province, NE China. The mineral occurs in a green-aegirine nepheline syenite as non-metamict grains and is associated with microcline, nepheline, aegirine, biotite, eudialyte, rinkite and titanite. The anhedral crystals are several hundred micrometres in size. The mineral is black with dark-brown streak. It is translucent with a resinous luster. Cleavage or parting was not observed. It is brittle with a conchoidal fracture. The hardness is VHN _(100) 683-964 kg mm ~(-2) (5.5-6 on Mohs' scale). The measured density is 4.28 g cm ~(-3), and the calculated value is 4.30 g cm ~(-3) from the empirical chemical formula. Optically, hezuolinite is biaxial negative, with n > 1.8 and 2V = 75 °. The dispersion is strong with r. v. The mineral shows a strong pleochroism, from pale brown to dark brown. The average of twenty-five analyses leads to the empirical formula (Sr _(2.15)Ce _(0.55) La _(0.49) Ca _(0.49)Na _(0.12)Nd _(0.09) Pr _90.03)Th _90.03)Sm _(0.01) Eu _(0.01))∑ _(3.98) (Zr _(0.82) Fe _(0.14)~(2+) Hf _(0.02)Mn _(0.01)) ∑ _(1.00) (Ti _(1.38) Fe _(0.36)~(3+) Fe _(0.14)~(2+) Al _(0.04) Nb _(0.02))P _(1.94)Ti _2O _8 (Si _(2.01)O _7) _2, on the basis of O = 22. The simplified formula is (Sr,REE) _4Zr(Ti,Fe ~(3+),Fe ~(2+)) _2Ti _2O _8(Si _2O _7) _2, ideally Sr _2REE _2Zr(Fe ~((2+))Ti _3O _8(Si _2O _7) _2. The five strongest reflections in the X-ray powder-diffraction pattern [d in ?(I)(hkl)] are: 2.98(100)(204), 3.02(90)(313), 1.96(90)(024), 2.18(40)(-422), and 2.84(70)(020). The structure was solved and refined in space group C2/m, with α = 13.973(3), β = 5.6984(11), c = 11.988(2) ?, β = 114.10(1) V = 871.3(3) ? _3, Z = 2, to R1 = 0.037, wR2 = 0.097. The structure of hezuolinite is similar to rengeite. The changes of Sr-O, Zr-O and Ti(1)-O distances confirm partial substitutions of REE for Sr, and Fe for Ti. The sites of O(1), O(2) and O(3) of the hezuolinite structure (C2/m) are split into O(1) and O(1'), O(2) and O(2'), O(3) and O(3') sites in the rengeite structure (P21/a), respectively. The Si(1)-O(7)-Si(2) angle in hezuolinite is 175.8, and is significantly less bent than in rengeite (169.7 °). The observed systematic extinctions are in agreement with space group C2/m. Hezuolinite is a member of the perrierite-subgroup and can be considered as a chemical intermediate between rengeite and perrierite.