Prior to the recognition of ALH84001 as a Martian meteorite, EETA79001 was noted as the Martian meteorite that contained the most visible deposits of carbonate minerals. However, because the EETA79001 carbonates are ultrafine-grained (micrometer scale) (Gooding and Wentworth, 1991) and white in color, they are nearly impossible to recognize in thin section, compared with the much coarser-grained (millimeter scale), orange-colored carbonates in ALH84001. The only practical way to estimate the abundance of the predominant form of carbonates in EETA79001 is to map whole-rock surfaces for occurrences of the characteristic "white druse" (Martinez and Gooding, 1986) that is the volumetrically most significant habitat of carbonate minerals in EETA79001.

On November 21-25, 1996, the remaining inventory of "white druse" was estimated from existing whole-rock pieces of EETA79001, in a nitrogen glove box, using a binocular microscope. Using size-calibrated photographs of the specimens, and a size-calibrated eyepiece reticle in the microscope, "white druse" areas were measured on the surfaces of the specimens and mapped onto the photographs. The volumetric abundance of "white druse" was estimated as the map area of the druse normalized to the map area of the rock face. Results are summarized below (note possible summation discrepancies due to arithmetic roundoff).

These observations confirmed earlier observations (Martinez and Gooding, 1986) that the druse seems to be associated exclusively with veins and pockets of Lithology C, which consists of dark brown to black, glassy to cryptocrystalline material that is manifest as veins and vuggy, ovoid inclusions, predominantly in Lithology A. No "white druse" was observed on fusion crust or in any weathered exterior surface of the meteorite except those areas where the outer surface had been broken to reveal Lithology C.

Additional daughter samples of EETA79001 exist but were not mapped during this measurement campaign. However, it is clear that the abundance of white druse varies from one daughter sample to the next roughly according to the proportion of Lithology C. Based on results of the current survey, the most probable abundance of the druse averaged over all daughter samples should be on the order of 0.08 % by volume. Because the "white druse" is highly porous, its mass abundance probably is a factor of 2-3 lower than its volume abundance.

Researchers are reminded that pure extracts of "white druse" are not possible to prepare in the Meteorite Processing Laboratory at JSC. Instead, as has been the case for previous studies, "white druse" can be sampled for research only as coatings on rock chips that are rich in Lithology C.

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References:
Martinez R. and Gooding J. L. (1986) New saw-cut surfaces of EETA79001. Antarctic Meteorite Newsletter 9 (1), 23. JSC Curator's Office.

Gooding J. L. and Wentworth S. J. (1991) Origin of "white druse" salts in the EETA79001 meteorite. (abs) Lunar Planet. Sci. XXII, 461-462.