88-6, Chap. 8
Chert and/or cherty
stone (less than
2.50 sp. gr. SSD) f
and/or siltstone g
Total of all deleteri-
exclusive of mate-
rial finer than
No. 200 sieve
Chert is defined as rock composed of quartz, chalcedony, or opal, or any mixture
The texture is so fine that
It is variable in color.
of these forms of silica.
the individual mineral grains are too small to be distinguished by the unaided eye.
Its hardness is such that it scratches glass but is not scratched by a knife blade.
It may contain impurities such as clay, carbonates, iron oxides, and other min-
Other names commonly applied to varieties of chert are flint, jasper,
agate, onyx, hornstone, porcellanite, novaculite, sard, carnelian, plasma, blood-
Cherty stone is
stone, touchstone, chrysoprase, heliotrope, and petrified wood.
defined as any type of rock (generally limestone) which contains chert as lenses
and/or nodules or irregular masses partially or completely replacing the original
SSD = saturated surface dry.
Claystone, mudstone, or siltstone is defined as a massive fine-grained sedimentary
rock which consists predominately of clay or silt without lamination or fissility.
It may be indurated either by compaction or by cementation.
Shaly limestone is defined as a limestone in which shale occurs as one or more
thin beds of laminae. These laminae may be regular or very irregular and may be
spaced from a few inches down to minute fractions of an inch.
stone is defined as a limestone in which clay minerals occur disseminated in the
stone in the amount of 10 to 50 percent by weight of the rock; when these make up
from 50 to 90 percent, the rock is known as calcareous (or dolomitic) shale (or
claystone, mudstone, or siltstone).