It's hard to ID a pill with no imprints, but my guess is it's not a Morphine. As far as I know, there is no morphine out there with the description you gave.
you cannot positively ID it cause there is no marks...However when I had back pain my DR. at Kaiser gave me 10mg morphine pills and they were white and no marks on them they were about as big as a birth control pill...So they are out there they just can not be ID'd