micromineral
/ˌmʌɪkrə(ʊ)ˈmɪn(ə)rəl/ /ˌmaɪkrə(ʊ)ˈmɪn(ə)r(ə)l/noun
1 Geology. A mineral of microscopic size.
2 Biology and Medicine. An essential mineral nutrient required in relatively small amounts; a trace element.
Origin
Late 19th century; earliest use found in American Naturalist. From micro- + mineral.