Extraterrestrial rocks and olivine nodule

Iron-nickel alloy, troilite and chromite. Alta'ameem Meteorite, Iraq

Click hereRounded iron-nickel alloy (white, centre) contains silicate inclusions (grey) and shows incipient irregular alteration (lower reflectance patches, centre top). It is surrounded by troilite (brown, left) and minor chromite (light grey, centre bottom). A discrete fractured chromite (right) also contains silicate inclusions. The majority of the groundmass is pyroxene (dark grey).

Polished thin section, plane polarized light, x80, air

Taenite, kamacite and troilite. Alta'ameem Meteorite, Iraq

Click hereTaenite (cream) is the main phase; it is altered and tarnished along its margin (bottom right). Kamacite (blue-white, slightly higher reflectance, centre top) forms a wide rim about the top of the taenite and also shows alteration (left centre). Small crystals of troilite (brown, right) are present in the pyroxene-rich (dark grey) matrix.

Polished thin section, plane polarized light, x 140, air

Troilite, chromite and ilmenite. Alta'ameem Meteorite. Iraq

Click hereTroilite (brown, high reflectance, right) has crystallized around euhedral pyroxene crystals (right). Pyroxene (grey, centre) shows parallel cleavage and faint internal reflections. Chromite (light grey, centre) encloses a small ilmenite lath (brown, low reflectance, centre) oriented cast-west and both central chromite crystals show faint diffuse brown internal reflections.

Polished thin section. plane polarized light, x 160. oil

Ilmenite, spinel and iron-nickel alloy. Apollo 17, Lunar Sample 70181

Click hereA basalt fragment from the lunar regolith. Abundant subparallel ilmenite laths (pale brown), many of which are 'feather-like', lie within plagioclase (areas of light-coloured internal reflection, bottom right) which is intergrown with euhedral rhombic pyroxene (light grey, few internal reflections, left centre). Small euhedral equant chromite-ulvöspinel (pale brown, top left) and rounded iron-nickel alloy (white, very high reflectance, bottom left) are present in the plagioclase also. The high magnification and large variation in reflectance between the opaque phases makes accurate colour photography difficult.

Coarse grain mount, plane polarized light. x 400, oil

Chromite, ulvöspinel and iron-nickel alloy. Apollo 12, Lunar Sample 12002

Click hereSubhedral chromite (green-grey, centre) cores are enclosed within ulvöspinel rims (brown-yellow, centre left). Iron-nickel alloy (white, high reflectance, bottom control forms rounded inclusions in the spinel phases. Pyroxene (light grey) shows strong internal reflections (right). Plagioclase (dark grey, left) shows weakly developed internal reflections.

Polished thin section. plane polarized light. x 400. oil

Spinel. Calton Hill, Derbyshire, Britain

Click hereAn olivine nodule within alkali olivine basalt. Chrome-rich spinel (light grey, highest reflectance, top centre and left, bottom centre) has a complex symplectite-like intergrowth with coarse-grained olivine (centre and right) which has a slightly lower reflectance than spinel but shows internal reflections and alteration to 'serpentine' along fractures (low reflectance, bottom right). Spinel is surrounded by fine-grained pyroxene (poorly polished areas). In transmitted light the spinel is brown.

Polished thin section, plane polarized light, x 80, air