The chalcedony group is a well-known group of minerals including agate, heliotrope, onyx, and carnelian. Chalcedony is common in geodes and in cameos and intaglios.
Main article- Agate
Agate is a banded variety of chalcedony. Agate is common in metamorphic and volcanic rocks. It and jade are two common minerals for carving. Mexican agate is sometimes called "Cyclops agate". Moss agate is a well-known agate variety.
Main article- Heliotrope
Heliotrope, usually called bloodstone, is a black variety of chalcedony with red spots. The primary source of heliotrope is in India. Sometimes heliotrope has yellow spots, this heliotrope being called plasma.
OnyxEditMain article- Onyx
Onyx, like agate, is a banded chalcedony. The color of onyx bands can be nearly every color. Sardonyx is a kind of onyx with reddish bands. Black onyx with no bands is the most famous variety. The name "onyx" is sometimes used to label other banded lapidary minerals such as calcite.
CarnelianEditMain article- Carnelian
Carnelian is a well-known red chalcedony. It is sometimes used as a gemstone. It is sometimes mistaken for a kind of chalcedony called sard.