Is there any reason 'A stone is near the tree' shouldn't be accepted?

articles are not part of russian and should not count as errors

Yes. Same here. Show me the difference between"a stone" and "the stone".

"A stone near a tree?"

How can one day "there is a stone close to the tree"? Thanks!

I wonder... I've seen 'у' used as 'near' before... what's the difference between возле and у?

Particularly when my Russian mother in law is being demanding, these sentences seem most Faithfully translated in cave-man English :

"Stone. Near. Tree."

Why is дерево in the genetive and not the prepositional case?