FMF - Friends of Minerals Forum, discussion and message board

[Roger Warin]

Extraterrestrial olivine (pallasitic peridot)
Crystal of olivine from Jepara pallasite, found in Java in 2008.
The parallel lines are planar deformations resulting from impacts.
Mineralogy is the same on asteroids.
Roger.

[alicerobert]

what is difference between olivine and yellow spire... both look like pretty same.
And can you tell me which one is more costly and why??

[Jesse Fisher]

Olivine is the name for a group of anhydrous iron and magnesuim-rich minerals (forsterite being the Mg-rich member and fayalite being the Fe-rich member) that are commonly found in igneous rocks such as basalts, some high-grade metamorphic rocks, and as in the example above, some types of meteorites. The name for the olivine minerals in the gem trade is "peridot." I am unfamiliar with the name "yellow spire" but it certainly sounds like another trade name to me, and may refer to the same mineral. People often coin trade names for some subtle variation of fairly common stones in order to make them sound more unique, and thus more desirable and costly. But then, that's marketing, not mineralogy.

[lluis]

Hi, Alice, Jesse

Maybe being foreigner I understood the yellow spire as "yellow sapphire".

If natural, yellow sapphire is expensiver than peridot (at least what I have seen; and refering to terrestrial peridot; extraterrestrial peridot, I suppose would be pretty expensiver....)
But as far as I know, there are many "yellow Sapphire" that are colorless ones cut and heated with beryllium. They are not exactly expensive, and maybe same or lesser price than a peridot.

Hope it serves

With best wishes

Lluís

[Roger Warin]

Hello Alice, Jesse, List,
If the mineralogy into asteroids is the same as on Earth, physics is not quite the same ... In this sense there may be high temperatures and high pressures. Thus, one of the parameters that characterize a meteorite is the shock level.
Of course, these factors also exist on Earth, but rarely (diamond formation). During impacts between asteroids, it may appear cracks in the crystal lattices. For pressures not exceeding 2 to 5 GPa, there are planar fractures (PF's). We know that in the Alps for example, the pseudo-cleavage according to face r {10.1} can appear into the quartz crystal.
If the pressure is even higher, 5-10 to 35 GPa, other lattice planes are affected. These deformations are visible in thin sections as sets of parallel lines that intersect. These are PDF's (Planar Deformation Features). Generally PDF's are "decorated" with tiny fluid inclusions or bubbles. They generally facilitate observation under optical microscope.
They also appear on Earth in quartz grains of impactites (formation of a meteoritic impact crater).
In this olivine inserted into a pallasite, the lines are cracks, physical defects in the lattice (without melt).
It’s difficult to cut such stones, because strain forces.
PF’s are microcracks, 3 microns wide.
These lines aren’t another olivine or an exsolution product, but only a physical defect, highlighted by light.
PF’s, and more frequently PDF’s, are reported in quartz, feldspars, olivine, pyroxenes and for terrestrial compounds, amphibole, apatite, garnet, silimanite, garnet, etc.

Roger.