Moorabie L3.8-an

A few of us were talking meteorites when one friend mentioned Moorabie. When I couldn’t recall the stone I was admonished to refresh my memory as soon as possible. I make amends with this column.

Even before checking my small collection I consulted David Weir’s Moorabie page to see what the score was. He lays out the reasons for the “anomalous” classification and why the “L” designation is a bit tentative. Researchers make a good case for Moorabie being from an ordinary chondrite parent body other than the H, L and LL PBs.

While the parent body was still plastic it sustained a deforming impact that oriented its components. This slice appears to have been compressed from the top and bottom. Moorabie L3.8-an.

That same preferred orientation is apparent here with formerly spherical chondrules now ovoid. Moorabie L3.8-an. Cross polarized transmitted light (XPL)

The fibers in this radial pyroxene chondrule appear to have been bent by the impact. Moorabie L3.8-an. XPL.

Moorabie is strongly shocked, S4-5. This is unusual for an unequilibrated chondrite. The shock has tweaked the crystal lattice of this olivine fragment such that it does not go into extinction uniformly when the polarizing filters are rotated. Instead it darkens then lightens in a patchwork. XPL.

This is a sequence of images of the same olivine fragment as it is viewed through stages of optical extinction in cross polarized transmitted light. This shock induced extinction pattern is called mosaicism. Moorabie L3.8-an.

A distorted barred olivine chondrule. Moorabie L3.8-an. XPL.

A 3 mm long porphyritic olivine chondrule, by far the dominant type of chondrule in Moorabie. XPL.

At lower right is a radial pyroxene chondrule that was distorted, broken and altered before being sectioned for our viewing pleasure. Moorabie L3.8-an. XPL.

A dark clast with fine mineral grains. Moorabie L3.8-an. XPL.

Metal and brassy troilite (FeS). Moorabie is relatively troilite-rich. Field of view is 2 mm wide. Reflected light.

A granular olivine chondrule containing metal blebs. Field of view is 2 mm wide. Reflected light and transmitted cross polarized light. Moorabie L3.8-an.

The white surrounding the minerals in the center of this photo is glassy material, possibly maskelynite which is known to occur in melt pockets in Moorabie. Partially crossed polarized light.

John Kashuba

John is a natural history enthusiast living in Oregon.