Onyx is the parallel-banded variety of chalcedony, a silicate mineral. Agate and onyx are both varieties of layered chalcedony that differ only in the form of the bands; agate has curved bands while onyx has parallel bands. The colors of its bands range from black to almost every color. Specimens of onyx commonly contain bands of black and/or white. Onyx, as a descriptive term, has also been applied to parallel-banded varieties of alabaster, marble, calcite, obsidian, and opal, and misleadingly to materials with contorted banding, such as "cave onyx" and "Mexican onyx".

Alabaster is a mineral and a soft rock used for carvings and as a source of plaster powder. Archaeologists, geologists, and the stone industry have different definitions and usages for the word alabaster. In archaeology, the term alabaster is a category of objects and artefacts made from the varieties of two different minerals: (i) the fine-grained, massive type of gypsum, and (ii) the fine-grained, banded type of calcite.