> concretions:
There
are several kinds of crystallisation in caves.
They are found in great abundance in the Grotte de Clamouse.
-
stalactites and stalagmites develop
vertically by deposits of the limestone in the water:
- stalactites grow downwards: they are fed by water
dripping through a narrow central tube and often on the outside too, so
they grow in diameter and length at the same time.
-
"straws" are stalactites fed only through the
inside, so their diameter remains constant, a bit less than a
millimetre.
-
columns or pillars are
made when a stalactite and stalagmite meet and join up.
-
stalagmites grow upwards. Water that drips
from a stalactite or from the roof drops onto and spreads over the
stalagmite, which grows mainly at the top and a bit over the sides.
-
stalagmitic floors are formed by fine sheets
of water flowing over sloping walls and floors leaving thin stratified
deposits of limestone.
-
draperies are like stalactites but without a
tube through the middle; their growth is external and the surplus water
drips onto the floor to form stalagmites on the stalagmitic floor.
-
supersaturation of limestone in the water can also form concretions
called rimstone pools, where crystals build up on
the bottom and sides and around the edges. They are very noticeable in
a dried-out rimstone pool in the White Corridor in Clamouse.
-
where the water supply is too low, it does not drip, but stays on its
support; in this case, the limestone is deposited into fine concretions
solely by evaporation and its development depends on the way the water
spreads before evaporation, the laws of crystal growth, any draughts
boosting evaporation and capillary forces which can direct the way the
water is expelled. The concretion, called "helictite",
has no reason to develop vertically, so it grows in all directions.
When all these conditions are combined, huge sheets of crystals and
helictites can be deposited.
-
in mineral terms, crystals of limestone deposited in caves can be in
two different basic forms: calcite and aragonite.
Most cave crystallisations are calcite, aragonite is much rarer and
forms into tufts of crystals such as those in the White Corridor of the
Grotte de Clamouse.
Aragonite is widespread in Clamouse, due to the presence of magnesium
in the dolomitic rock the cave is cut into. All these types of
concretion are found in the Grotte de Clamouse.
