Environmental Engineering Reference
In-Depth Information
Ironstone
Ironstone is a form of limonite found in some coastal plain formations as discontinuous
beds usually from about 3 to 6 ft thick. It is hard, red-brown to reddish purple, and often
mistaken for bedrock in excavations or test boring. In the Atlantic Highlands of New
Jersey it caps the hills, making them very resistant to erosion (Figure 7.106).
In Brazil, the deposit is called “canga” and is common to the Tertiary coastal plain sed-
iments. North of Vitoria, in the state of Espirito Santo, the formation extends offshore for
about a kilometer, forming a reef that discontinuously follows the shoreline. Its extremely
irregular form is shown in Figure 1.107. Exposed as a capping deposit over the inland hills
of the Barrieras formation (Tertiary) from Espirito Santo to Bahia, 1000 km to the north, it
has the appearance of laterite and is typically found in cobble-size fragments.
Caliche (Calcrete)
Distribution
Caliche is common to hot, semiarid regions such as Texas, Arizona, and New Mexico in
the United States, and Morocco in Africa.
Description
Because many factors can affect its deposition, caliche is variable in form. In many areas it
may be a hard, rock-like material, and in others it may be quite soft. Characteristically
white or buff in color, it can be discontinuous or have large voids throughout, or be lay-
ered, or massive. A massive formation is illustrated in Figure 7.108. Typically it is not more
than a few feet or so in thickness.
Formation
An evaporite, caliche is formed when either surface water or groundwater containing cal-
cium or magnesium carbonate in solution encounters conditions causing the carbonate to
FIGURE 7.106
Ironstone deposit in Tertiary coastal plain soils (outcrop at arrow) (Atlantic Highlands, Monmouth County,
New Jersey).
 
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