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Earth  Geology
Rock Types Dolomite
Dolomite
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| Pitted black dolomite in
a glade on Iron Mountain. |
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| Gray dolomite with a white chert lens
in a road cut near Mansfield. |
The most common rock type in the Bryant watershed is
dolomite. Dolomite is usually quite deeply weathered and soil-covered. You
can find it making up much of the walls of the bluffs in the deeper valleys,
capped by the harder sandstone. Dolomite also crops out from the thin soil
of "glades" on hilltops and hillsides throughout the area. You'll recognize
it there as a dark grey to black, distinctly pitted rock.
Dolomite is composed of the mineral of the same name. The
mineral dolomite is a calcium-magnesium carbonate, CaMg(CO3)2. It is seldom
pure but contains variable amounts of sand, silt, clay and chert. These
"contaminants" occur as scattered grains and clumps and as layers or lenses
within the dolomite.
Dolomite is the dominant rock type of the Jefferson
City Formation, which forms the hilltops and higher elevations
of the watershed. Dolomite layers make up about half of the bluff-forming
Roubidoux Formation. Dolomite is also
the rock type of the exposed top layers of the Gasconade
Formation along the central part of the deepest valleys of the
Bryant.
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