ALH84001

The two masses 0 and 65, plus chips and fines samples 2, 14, 17, 21, 39, 40, 41, 59, 69, 76, 103, 147, 176 and 202 were surveyed for the distribution and textures of carbonates. Due to time constraints, a truly thorough job could not be done. Also, the working conditions (looking through the cabinet glass at a sample that is difficult to manipulate) did not allow good, close inspection. This should be considered a report of a reconnaissance survey.

Summary:
Carbonates can be divided into two main textural types, rounded, zoned blobs (rzb), a.k.a. globules, rosettes, etc., and irregular patches.

The rzb typically occur in clusters that can contain ~20 in an area of ~10 mm². These are typically found on smoothly undulating, polished looking translucent grayish surfaces with a sugary texture. These are fracture surfaces. In one spectacular area on the broken face of 65, there are two fractures crosscutting at ~90° with rzb on both surfaces. These fractures also cross-cut a crushed zone defined by streaked chromite.

"Irregular patches" is a catch-all term for everything else, and this textural type could probably be subdivided with careful study. These are, obviously, irregular shaped regions of carbonate. Some are approximately equidimensional in 2D, others are highly linear. Some of them are certainly composed of a collection of fine grains, and many of the remainder appear to be too. Working constraints did not allow close inspection. Some of the irregular patches give the appearance of having been streaked by movement on the crushed zones, but possibly they simply formed in that shape. A few "veins" were seen. One of these seemed to be composed of coarser grained carbonates, like the rzb, and possibly is consistent with an edge-on view of a region of rzb.

Carbonates are more-or-less uniformly distributed in ALH 84001. The broken face of 0 seemed to contain more numerous carbonates than the broken face of 65. (I do not think a reliable estimate of carbonates can be made from the saw-cut faces because the phases on them are difficult to distinguish.) A carbonate region can be found on virtually any 1 cm² area of 0, but not on 65. Among the chips and fines samples, some obviously contain more numerous carbonates than others. Nevertheless, there are no portions of the rock that can be considered "carbonate mines." My estimate is that on a scale of ~100 grams (about 1/20th of the rock), the carbonate abundance doesn't vary by more than a factor of 3 or so from an estimated average area abundance of ~1 %. Some of the chips and fines samples appeared to contain unusually high abundance of rzb relative to irregular patches of carbonates, but these samples were not unusually rich in carbonates as a whole.

I did not think I could reliably determine what the mineral substrate hosting the carbonates was. Some were obviously on maskelynite substrates.

I briefly examined the regions on 0 and 65 where the slabbing attempt failed, and compared 69 (the failed slab) with the other masses and chips and fines. I could not see any gross textural distinction between the area around where the slab broke and the remainder of the rock. In my opinion, there is nothing texturally unique about this portion of the rock. I also do not think carbonates in this region are any more abundant than in the rock as a whole.