|This rock (77 mm width) is fully packed with specimens of E. tenera.|
|This polished slab (37 mm width) shows only the|
cross section of shells of E. tenera.
|These three specimens of E. tenera are internal casts (i.e., each one shows |
only the interior of a shell, which was filled with chalcedony).
The largest specimen is 14 mm height.
There has been considerable disagreement in blogs and websites as to whether or not the E. tenera specimens, found in rock shops, have been replaced by chalcedony or agate. Technically speaking, chalcedony is the “culprit.” It is a microcrystalline form of silica, and chalcedony has many varieties, including agate, which commonly has multi-colored curved or angular banding. The specimens of E. tenera that I have seen were replaced by a fairly uniform brown or gray color of “ordinary” chalcedony and not replaced by the more eye-catching, beautiful colors typically associated with agate.
|Elimia tenera: Specimen on the left (19 mm height) shows the spiral ribs, and the|
specimen on the right (14 mm height) shows both spiral and radial ribs.
Genus Elimia belongs to family Pleuroceridae, and, as currently defined, this family today is confined entirely to North American fresh waters: The eastern United States and into Texas and from southern Canada to Florida. Pleurocerids might be relicts (“living fossils”) from earlier geologic times (Paleozoic?) in eastern North America.