Faceting Pallasite Peridot

By Nancy L. Attaway

Every once in a while, the opportunity arises that allows a facetor to work on extremely rare gem material. In this case, a meteorite dealer presented me with two pieces of pallasite peridot to facet for a private collection.
Pallasite is the unique combination of an iron-nickel alloy with olivine, a meteorite dotted with interplanetary peridot dated at 4.5 billion years old. The German geologist, Peter Simon Pallas (1741-1811) wrote the first description of this material in 1776 using a piece found in Siberia. The best known finds of pallasite were discovered in South America, in Chile’s Imalac and in Argentina’s Esquel. Many of the olivines in pallasite are barely thick enough to facet, which is why pallasite is mostly seen as slabs that can be set in pendants, sometimes accented with diamonds. These slabs resemble stained glass windows. The facetable pieces usually yield stones between 10 to 30 points and exhibit a drab shade of olive green.

Geologists explain meteorites as chunks of original solar system material that once orbited the sun in an attempt to form another planet between Mars and Jupiter. However, these blocks were unable to merge into a planet due to the enormous gravitational field around Jupiter, and they remained in orbit as asteroids. It is thought that pallasite sustained meltdowns in outer space while still in the asteroid stage, and this effect caused the iron-nickel cores to fuse with the olivine mantles. One possible theory for the meltdown is the intense heat produced by the quick-decaying radioactive isotopes in the original material. The resulting high temperatures pushed the metal in the core out toward the mantle and then mixed it with the olivine from the mantle at the interface between the mantle and the core.

When I examined the two pieces of pallasite peridot, I found that one was thick enough to render a traditional pavilion and still keep the critical angle in mind. The other one had the appearance of an irregular triangle with not much depth. I enjoy faceting peridot, but these two would certainly challenge me. Both contained darkened areas and serious cracks that would definitely present me with faceting problems.

Using a nearly-new 600-grit dyna lap and a 96 gear index wheel on my Facetron, I carefully shaped the thicker one into a 6.5 x 6.5 mm. cut-corner square. I modified the square barion design and cut at 55 degrees the four facets: 96, 24, 48, and 72. The corner facets: 12, 36, 60, and 84 were cut at 44 degrees, and the facet pairs: 93 and 3, 21 and 27, 45 and 51, 69 and 75 were cut also at 44 degrees. I cut twelve long slivers of facets at 43 degrees on facets: 9, 15, 33, 39, 57, 63, 81, 87, 96, 24, 48, and 72 for a starburst culet. After transferring to the crown, I cut two rows of parallel step facets, one at 45 degrees and one at 35 degrees, and then I cut a table.

I wished that I had room for a tiny parallel row of step cuts at 25 degrees. I really like to have those on squares and emerald cuts, as they give that extra detail. There really was not enough room for them, and I wanted to leave a thick girdle. I also did not want any of the internal inclusions coming to the surface as pits or chips, and I cut the crown just enough to keep them contained within the stone. A good polish was accomplished with 60,000-grit diamond slurry on the Last Lap.

The finished square gem weighs 1.29 carats and sparkles. The modified angles reflect the light with no windowing, although the table is a bit too large. Only one of the inclusions rose to the surface, where one small piece of a veil came off from a corner girdle facet during polish. I saw its small outline before I polished it, and, subsequently, a tiny piece fell out of a cut corner girdle facet.

I attempted to facet the other one in the apollo-cut triangle, a neat and simple cushion-cut design. I had cut two sides on the pavilion when the third side crashed. The darkened area with cracks broke from the stone and broke a small chunk from the second side. I polished what facets I could and placed the dopped stone in acetone to loosen it from the dop. To eliminate the resulting damage, I re-dopped the stone to cut a series of facets fanning out in an arc at 55 degrees with corresponding girdle facets. I cut only a table facet on the crown. The finished stone weighs 0.28 of a carat and resembles a shield. The idea of fanning out a series of facets in an arc at 55 degrees worked well to reflect the light.

Steve was very happy with the square starburst design, and he was quite surprised that I rendered a stone at all from the second piece. In both designs, I had to consider carat retention, facet composition, and overall beauty. The use of a 600-grit dyna lap left little subsurface damage and allowed a polish to quickly appear. The crystal integrity of peridot can show the effects from the origins of its very violent past.Whether it is from Arizona, Pakistan, or outer space, peridot can be both beautiful and unpredictable.