What's wrong with using black marble as a door cover?

From the perspective of chromatics, it is not necessary as long as it passes the test from the perspective of radiation. You should know that almost everything we can touch has radiation, including ourselves, as long as the intensity is harmless to the human body.

From the perspective of geomantic omen, we should still consider the space size, housing pattern, gate orientation, etc. Actually, it is not necessarily impossible.

There may be some opinions about pure superstition. I'm not sure. If the old people at home say that they are unlucky, they must change it from the perspectives of family harmony, neighborhood relations, filial piety and caring for the elderly, or seek the advice of the old people to deal with it. Harmony is the most important thing!