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I was reading a bit about the fluid mechanics of volcanoes to further understand some of the dynamics of "magma wagging" from my earlier question.

From [2]:

Heterogeneous nucleation, in which the presence of certain crystals (e.g., Fe-Ti oxides) provides nucleation substrates because they lower surface tension, can greatly reduce $\Delta p_{s_{crit}}$ to less than a few megaPascals (Gardner & Denis 2004, Hurwitz & Navon 1994).

I became curious as to what was so special about the Fe-Ti oxides that makes them good nucleation sites, so I looked up [1]. I stumbled upon a different problem, though. In their procedure, they claimed:

Fe-Ti oxides are either blocky or needle-shaped. Blocky ones are 0.5–5$\mu$m in size and those large enough were identified with an electron microprobe as titano-magnetite, here after referred to as magnetite.

Do mixed Fe-Ti oxides essentially have the same physical properties as magnetite? If the physical properties are in fact even slightly different, why would they be lumped together for analysis in these nucleation studies?

References:

  1. Gardner, J.E. and Denis, M-H. (2004) Heterogeneous bubble nucleation on Fe-Ti oxide crystals in high-silica rhyolitic melts. Geochimica et Cosmochimica Acta, 68:7, 3587–3597. [DOI]

  2. Gonnermann, H.M. and Manga, M. (2007). The fluid mechanics inside a volcano. Annu. Rev. Fluid Mech, 39, 321–56. [PDF] [DOI].

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In iron oxides, titanium commonly substitutes for iron in the crystal structure. Two solid solution series are important: the ulvöspinel-magnetite and ilmenite-hematite series.

The composition of a solution changes continuously, without any change in crystal habit. Your reference indicates its the size of crystals than matter for being efficient nucleation sites. Composition is not expected to be important.

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    $\begingroup$ I knew ulvospinel had the same structure as magnetite, but didn't release they also had a solid solution (learn something every day!) $\endgroup$ – winwaed Sep 5 '14 at 13:10

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