Altered magnetite and anatase. Derbyshire, Britain

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Magnetite (light brown) occurs as cruciform skeletal crystals as a result of rapid crystallization and is intergrown with plagioclase (dark grey and featureless). The pale body colour of the magnetite is due to oxidation and incipient alteration to haematite. Anatase (light grey, centre top) is abundant, forming aggregates of small crystals with strong yellow-grey internal reflections. Most of the anatase in this photograph is below the surface of the section and is seen by its internal reflections. It is associated with titanaugite crystals (featureless to pale internal reflections).

Polished block, plane polarized light, x 160, oil

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