Calcified object unsure

I have a question and I have been searching for an answer for a long time. I hope someone can help. I passed a yellowish/white calcified bumpy ovalish object in my stool. When I broke it open, it had a black small piece in it. Almost like a baby slug but not. It crumbled easily when pressed. Does anyone know what this could be or had this before? 7 days ago I took two days of Black-Walnut . And the past 5 days I've been taking garlic pills. TIA Tweet