Chalcedony comes in many colors from the common tannish-grey often found on rock outcrops to greens and purples, reds and tans. People have given separate names to the various colors - bloodstone when there is spotted red (guess where that name comes from), carnelian when a bright red, a dirty brown chert when the quartz mineral is mixed with clay, bright apple-green chrysoprase, and jasper which is generally opaque. The naming is subjective - but these stones are among the oldest used in jewelry and some named as birthstones. You can find out more about the various types of silica in the Quartz: By Any Other Name.

Chalcedony, Jasper, and Agate are only three forms of very, very fine-grained quartz - the crystals are there, but so tiny that it exhibits none of the crystal shape - just the hardness of quartz with a translucent luster. Agate is banded or shows other structures and chalcedony is generally non-banded. Jasper is generally opaque due to inclusion of clay. The names are not important – they are made of the elements silica and oxygen, and each has the mineral structure of quartz.

Hesse, Reinhard. “Silica Diagenesis: Origin of Inorganic and Replacement Cherts.” Earth Science Reviews, 1989. https://doi.org/10.1016/0012-8252(89)90024-X

Pabian, R., Jackson, B, Randy, P and J Cromartie, 2006,Agates, Treasures of the Earth,Firefly Books, 184 pp.

California, United States

This is a fairly elusive rock to pin down. The locality attached to this is California. The literature has this type of jasper from Arizona, so I imagine this is right over the California border.

This one needs more research – but it is a beautiful and unusual form of SiO2.

Somewhere in the Desert

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