Here's why:

* Carnelian is a variety of chalcedony, which is a microcrystalline form of quartz.

* Quartz is a mineral that is often found in sedimentary rocks, formed by the accumulation and cementation of mineral grains.

* Carnelian's distinctive orange-red color comes from impurities like iron oxide, which are commonly found in sedimentary environments.

While it's true that quartz can also occur in igneous and metamorphic rocks, carnelian's formation process and characteristic color strongly suggest its sedimentary origin.