@rexan20, black stools could be caused by food, supplements, medication, or minerals. Iron supplements, taken alone or as part of a multivitamin for iron-deficiency anemia, may cause black stools or even green stools.
Read more here: https://www.verywellhealth.com/causes-of-black-stool-1941711

Black stool may indicate something more serious, like bleeding in the GI tract. If you are experiencing nausea, stomach upset, dizziness, or abdominal pain along with black stools, contact your doctor right away.

Could be what you are eating. Suggest having it checked by an MD just in case.