Hezuolinite, (Sr,REE)4Zr(Ti,Fe3+,Fe2+)2Ti2O8(Si2O7)2, a new mineral species of the chevkinite group from Saima alkaline complex, Liaoning Province, NE China
Yang, Zhuming; Giester, Gerald; Ding, Kuishou; Tillmanns, Ekkehart
European Journal of Mineralogy Volume 24 Number 1 (2012), p. 189 - 196
published: Feb 1, 2012
ArtNo. ESP147052401016, Price: 29.00 €
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 VHN100 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 (Sr2.15Ce0.55 La0.49 Ca0.49Na0.12Nd0.09 Pr0.03Th0.03Sm0.01Eu0.01)Σ3.98 (Zr0.82 Fe2+0.14Hf0.02Mn0.01) Σ1.00 (Ti1.38 Fe3+0.36Fe2+0.14 Al0.04 Nb0.02)Σ1.94Ti2O8 (Si2.01O7)2, on the basis of O = 22. The simplified formula is (Sr,REE)4Zr(Ti,Fe3+,Fe2+)2Ti2O8(Si2O7)2, ideally Sr2REE2Zr(Fe2+)Ti3O8(Si2O7)2. The five strongest reflections in the X-ray powder-diffraction pattern [d in Å (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 a = 13.973(3), b = 5.6984(11), c = 11.988(2) Å, b = 114.10(1), V = 871.3(3) Å3, 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.