Premium
Kaitianite, Ti 3+ 2 Ti 4+ O 5 , a new titanium oxide mineral from Allende
Author(s) -
Ma Chi,
Beckett John R.
Publication year - 2021
Publication title -
meteoritics and planetary science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.09
H-Index - 100
eISSN - 1945-5100
pISSN - 1086-9379
DOI - 10.1111/maps.13576
Subject(s) - corundum , rutile , allende meteorite , titanium , mineral , stoichiometry , oxide , materials science , mineralogy , chondrite , oxygen , oxide minerals , analytical chemistry (journal) , inorganic chemistry , chemistry , metallurgy , chemical reaction , meteorite , physics , organic chemistry , chromatography , biochemistry , astronomy
Kaitianite, Ti 3+ 2 Ti 4+ O 5 , is a new titanium oxide mineral discovered in the Allende CV3 carbonaceous chondrite. The type grain coexists with tistarite (Ti 2 O 3 ) and rutile. Corundum, xifengite, mullite, osbornite, and a new Ti,Al,Zr‐oxide mineral are also present, although not in contact. The chemical composition of type kaitianite is (wt%) Ti 2 O 3 56.55, TiO 2 39.29, Al 2 O 3 1.18, MgO 1.39, FeO 0.59, V 2 O 3 0.08 (sum 99.07), yielding an empirical formula of (Ti 3+ 1.75 Al 0.05 Ti 4+ 0.10 Mg 0.08 Fe 0.02 )(Ti 4+ 1.00 )O 5 , with Ti 3+ and Ti 4+ partitioned, assuming a stoichiometry of three cations and five oxygen anions pfu. The end‐member formula is Ti 3+ 2 Ti 4+ O 5 . Kaitianite is the natural form of γ‐Ti 3 O 5 with space group C 2/ c and cell parameters a = 10.115 Å, b = 5.074 Å, c = 7.182 Å, β = 112°, V = 341.77 Å 3 , and Z = 4. Both the type kaitianite and associated rutile likely formed as oxidation products of tistarite at temperatures below 1200 K, but this oxidation event could have been in a very reducing environment, even more reducing than a gas of solar composition. Based on experimental data on the solubility of Ti 3+ in equilibrium with corundum from the literature, the absence of tistarite in or on Ti 3+ ‐rich corundum (0.27–1.45 mol% Ti 2 O 3 ) suggests that these grains formed at higher temperatures than the kaitianite (>1579–1696 K, depending on the Ti concentration). The absence of rutile or kaitianite in or on corundum suggests that any exposure to the oxidizing environment producing kaitianite in tistarite was too short to cause the precipitation of Ti‐oxides in or on associated corundum.