Not only are chalcedony, opals, and agates found among them, but many approach the condition of jasper and onyx.
"The Book of the National Parks" by Robert Sterling Yard
Outside on the platform between west and east, between flame and dark, Shway Dagohn showed now like one cutting from a jasper opal.
"Where the Pavement Ends" by John Russell
Blocks and logs of agate, chalcedony, jasper, opal and other silicate deposits lie in hundreds over an area of 60 sq.
"Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 5" by Various