Ilmenite Exsolution Research Articles

Electron-probe investigation of some intergrowths in iron-titanium minerals from Rosetta black sands

The nature of exsolution of ilmenite in titanomagnetite and of the alteration of ilmenite in Rosetta black sands was investigated by the electron micro-probe analyzer. The mode of formation of such micro-intergrowths has been explained and mainly attributed to oxidation processes.

A Detailed Opaque Petrological and Magnetic Investigation of a Single Tertiary Lava Flow from Skye, Scotland?II Spatial Variations of Magnetic Properties and Selected Relationships between Magnetic and Opaque Petrological Properties

Summary Natural remanence, initial susceptibility, saturation magnetization and strong field thermal properties have been measured on 45 basalt cores representing two vertical sections through the flow separated horizontally by 16 m. The form and magnitude of the profiles for every magnetic property differ in the two sections, which means that lateral variations are quite comparable to vertical variations in this lava. Stability of rernanence, as determined by a.c. partial demagnetization, is found to be related to two opaque petrological properties. High stability is associated either with titanomagnetite high-temperature oxidation (ilmenite exsolution etc.) or with titanomagnetite granulation. Granulation consists of areas of titanomagnetite replaced by fine aggregates of rutile and is described in detail in Part I of this paper. A relationship exists between strong field heating curves and natural titanomagnetite high-temperature oxidation. The Curie point spectrum has two isolated peaks. As natural oxidation increases the relative intensity of the high Curie point component increases. The possibility of titanomagnetite granulation, believed to be formed several million years after lava eruption, causing remagnetization is discussed and rejected. 1. Magnetic properties measured Natural remanence direction and intensity, weak field susceptibility, saturation magnetization and strong field Curie points have been measured for all the samples described in Part I of this paper. With the exception of natural remanence directions, these properties together with derived parameters and opaque petrological properties are listed in Table 1. Mean natural remanence directions for 32 oriented samples at different a.c. fields are listed in Table 2. Natural remanence values were measured for each specimen at several a.c. fields using an astatic magnetometer. From the changes in intensity and direction of natural remanence during a.c. partial demagnetization to 200 peak oersteds a cumulative stability factor, S2,,,,, has been obtained. Definition of S has been given by Wilson, Haggerty & Watkins (1968). Briefly, a sample suffering change in neither

A Correlation Between Remanent Magnetism and Petrological and Chemical Properties of Tertiary Basalt Lavas from Mull, Scotland.

A description is given of a petrological examination of a set of normally and reversely magnetized samples from tertiary basalt lava flows on the Isle of Mull. The collected evidence suggests that the normally magnetized samples are most likely to retain part of their original thermo-remanence. The reversely magnetized samples probably acquired their magnetization during a diffusion process in the opaque minerals which took place at an undetermined time after the consolidation of the lavas. The distribution of four features is found to correlate with the two senses of natural remanent magnetization. These features are the alteration products of decomposed olivine, the grain size and crystal form and the internal nature of the primary opaque minerals—especially exsolution of ilmenite from titanomagnetite. Normally magnetized samples are found to contain olivine replaced only by serpentinous minerals together with relatively small well-crystallized, optically-homogeneous (unexsolved) primary magnetite grains. On the other hand, reversely magnetized samples are found to contain olivine replaced by serpentine, secondary iron oxides and a red hydrated iron oxide (iddingsite). In addition, the primary magnetite grains in this group are relatively large, show poor crystal form and are typified by varying amounts of ilmenite exsolved as lamellae in the octahedral planes of the magnetite.