Final answer:
Onyx is composed mainly of quartz and feldspar, along with minor amounts of other minerals. It has a dark, smooth, and massive appearance and breaks easily.
Step-by-step explanation:
The main component of onyx is quartz. Onyx is an igneous rock that is composed mainly of quartz and feldspar, along with minor amounts of other minerals such as hornblende and biotite. It has a dark, smooth, and massive appearance and breaks easily. Onyx also has a dark, oily smell.