Onyx primarily refers to the parallel banded variety of the silicate mineralchalcedony. Onyx is a variety of layered chalcedony that differ only in the form of the bands. Onyx has parallel bands, the colors of its bands range from white to almost every color.
Marble is a metamorphic rock composed of recrystallized carbonate minerals, most commonly calcite or dolomite. Marble is typically not foliated, although there are exceptions. In geology, the term "marble" refers to metamorphosed limestone, but its use in stonemasonry more broadly encompasses unmetamorphosed limestone.