Oxidation of anosovite at temperatures 43003C produces new phases of general composition M n O 2n؊1 , based on unit cell intergrowth of M 3 O 5 and anatase structural elements. The structural principles on which the intergrowth series are based were established by analysis of high-resolution transmission electron microscope images. The structure for the dominant intergrowth phase, with composition M 6 O 11 , was re5ned using the Rietveld method applied to powder X-ray data. This phase has monoclinic symmetry and space group C2/m, with a ؍ 9.946(2), b ؍ 3.744(2), c ؍ 20.994(3) A s , and ؍ 93.30(1)3. Its structure comprises planar intergrowth of M 3 O 5 compositional blocks with the pseudobrookite-type structure and MO 2 compositional blocks with the anatase-type structure, parallel to (001), (001) M 3 O 5 ,(101) an . Alternatively, the structure can be considered as chemically twinned anatase with (101) an as the twin composition plane. The anatase blocks are alternately 2-octahedra and 3-octahedra wide along [001]. Local regions corresponding to compositions M 5 O 9 (twinned anatase blocks are 2-octahedra wide) and M 7 O 13 (3-octahedra wide anatase blocks) were also observed in TEM images. The results have relevance to the digestion of high-titania slags (anosovite-rich) in the sulfateroute titania pigment process because high sulfuric acid solubility is maintained after the low-temperature treatment, while the preoxidation of trivalent titanium avoids acid consumption by solution oxidation.