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DESCRIPTION: Primarily, agate is conspicuously banded
chalcedony; the bands range from parallel to highly uneven,
even within some individual specimens. Both color
and light transmission commonly differ from band to band. In
addition, chalcedony with variously shaped splotchy areas, commonly
having arborescent shapes are called agate, usually moss agate.
The term fossiliferous rock may be
applied to any fossil-bearing rock. Those mentioned herein are only a
few examples of many that have been used as gemrocks. Some
fossiliferous rocks have been selected for use as gemrocks because of
the identities of their contained fossils; others have been chosen
because of the patterns their included fossils give when cut in certain
directions. The name usually applied to these rocks in the marketplace
is the name of the rock preceded by either the name of the predominant
fossil (e.g., coraline marble) or the adjective fossiliferous if the
rock contains more than one kind of fossil with none predominant (e.g.,
fossiliferous limestone). Several other names, however, have
been used, most of them based either on the locality from which the
rock came or someone's idea of a term that might increase sales of
anything made from the rock. Because each of these gemrocks is
so-to-speak unique, descriptions, noteworthy localities, etc. are
included in the comments given after several of the materials listed
under the OTHER NAMES subheading.
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