Minerals Found in Caves
Many interesting minerals are found in caves in addition to the calcite
which forms the major features. Aragonite, a calcium carbonate mineral
similar to calcite but not as common, often occurs in intricate needles
known as anthodites. Gypsum (calcium sulfate) and related calcium sulfate
minerals are next to calcite in abundance. Some caves, although they are
developed in limestone, have extensive passages lined with fine, curling
growths of gypsum flowers. In other caves, selenite (a less common variety
of gypsum) forms long transparent rods or nests of fibrous crystals. Sulfates
of sodium and magnesium are also found in caves, although they are less
conspicuous than gypsum. Iron minerals in the form of oxides (limonite) and
hydroxide (goethite) occur in caves and in some places form stalactites.
Manganese minerals in caves are commonly present as thin, sooty coatings on
walls and ceilings and in earth fills. Nitrocalcite (calcium nitrate) is
abundant in earth fills in many caves, but individual fragments are generally
microscopic. Barite (barium sulfate) and celestite (strontium sulfate) also
occur in earth fills. In some solution caves, clay minerals exist in relatively
pure forms; these include the less common varieties attapulgite and endellite.
In deep caves encountered during mining operations, a number of ore minerals
have been found in the decorative wall draperies. Most common are azurite and
malachite (forms of copper carbonate). About 50 other minerals also have been
reported in cave deposits.
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