Criteria of ID: olive green to yellowish green color; viterous luster, harder than knife.
If a large olivine is found, it would be a semi-precious gem. Most olivine crystal are small in size as a particle of sand. This sample is in fact a rock with 98% olivine crystals. Dark color specks are augite.
Olivine mainly exist in mafic igneous rocks like gabbro or basalt. It is also the main mineral species in mantle rocks.
Olivine is very easily weathered.