Ibitira

Ibitira is the exception that nags us when we introduce people to the appearance of meteorites versus meteor wrongs. We like to say that if it has bubbles it isn’t the real thing, thus dismissing slag, lava and their cousins. But Ibitira and a few other exceptional meteorites do have vesicles.

Ibitira is exceptional also in that it is a eucrite not from Vesta. Vestoids are, by far, the largest of five groups of asteroidal basaltic meteorites believed each to have come from a distinct parent body:

Vesta – HED suite – howardite, eucrite, diogenite
Ibitira eucrite – and possibly NWA 2824 diogenite
Angrites – a small group, diverse yet related to each other
NWA 011 achondrite-ung – and pairings NWA 2400, 2976, 4901, 4587, 5644, 7129 Mesosiderites – but maybe also Vestian

Here are some photos of Ibitira.

Ibitira is mostly pyroxene, the brightly colored mineral grains. Plagioclase appears white to gray, sometimes mottled and elongated. Field of view is 3 mm wide. Thin section in cross-polarized light.

The large black oval zones are vesicles, bubble holes. Field of view is 3 mm wide. Ibitira Eucrite-mmict, thin section in cross-polarized light.

The parallel lines in the pyroxene show that two types of pyroxene have exsolved, that is they have unmixed. Here they are the calcium poor species, pigeonite and the calcium rich species, augite. Fields of view are 0.3 mm wide. Ibitira Eucrite-mmict, thin section in cross-polarized light.

Some smaller black areas are opaque minerals; other black areas are mineral grains in optical extinction because of the orientation of the crossed polarizing filters relative to their crystal lattices. Field of view is 3 mm wide. Ibitira Eucrite-mmict, thin section in cross-polarized light.

In plane polarized light we see which grains are actually opaque. Field of view is 3 mm wide. Ibitira Eucrite-mmict, thin section in plane-polarized light.

Opaque minerals in Ibitira include the iron titanium oxide, ilmenite; the iron chromium oxide, chromite; the iron sulfide, troilite; and iron-nickel metal. Field of view is 0.3 mm wide. Thin section in plane-polarized light.

Opaque material and stained transparent grains. Ibitira Eucrite-mmict, thin section in plane-polarized light.

In incident light we see that the dog shaped object is a bleb of metal and is the reason for the staining. Ibitira Eucrite-mmict.

A small assemblage of fine mineral grains. Ibitira Eucrite-mmict, thin section in cross-polarized light.

A small assemblage of fine mineral grains. Ibitira Eucrite-mmict, thin section in plane-polarized light.

A 24 mm wide slice of Ibitira. The vesicles are visible.

About the Author

John Kashuba
John is a natural history enthusiast living in Oregon.
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