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>Something we've mentioned on this list before is that gastroliths can
apparently be distinguished from non-gastoliths by firing laser beams
at them: the light-scattering effect of gastoliths differs from
non-gastroliths and can be detected. The paper that first reported
this (the technique was first used on moa gastroliths) was in
_Journal of Paleontology_: I don't have the citation with me now, but
it has been posted on the list.<

A long ago post by me:

>References for works on the use of light scattering to distinguish   
between gastroliths and non-gastroliths are posted below. The general   
conclusion from these articles is that the degree of polish on   
gastroliths is measurably different, using light scattering techniques,   
from that of stream polished rocks. The causes of the higher polishing is   
not investigated, but the contribution of digestive acids is suspected to   
play a role along with abrasion during gizzard contractions.

JOHNSTON, R.G., K. MANLEY, and C.L. LEMANSKI. 1990. Characterizing   
gastrolith surface roughness with light scattering. Optics   
Communications, 74:279-283.

MANLEY, K. 1991. Two techniques for measuring surface polish as applied   
to gastroliths. Ichnos, 1:313-316.

MANLEY, K. 1993. Surface polish measurement from bona fide and supsected   
dinosaur gastroliths and wave and stream transported clasts. Ichnos.   

JOHNSTON, R.G., W.G. LEE and W.K. GRACE. 1994. Identifying Moa   
gastroliths using a video light scattering instrument. Journal of   
Paleontology. 68(1):159-163.<