Apart from the green stones you produce other stones of different colour; black orange, brown, yellow ect... I think its these that are gall stones.
Show us a picture of stones of different colours; and then there chemical analysis.
Although stones are labelled gall stones, many stones come from the liver. They are gall stones and liver stones . The liver is a big oragan, and can account for the huge no of stones produced. Many peoples livers can be twice, thrice the size of what they should be.
Are the green stones manufactured from the olive oil. Perhaps, perhaps not? Coloured stones may be mixed and disguised in the green ones