CALCITE
The bulk of the cave formations that are seen in the caves are formed
from calcite. Calcite is the most common crystaline form of the mineral
calcium carbonate. As water seeps into a cave it carries with it dissolved
calcium carbonate. As the water is exposed to the atmosphere within the
cave it is able to release carbon dioxide as well as evaporate slightly.
The result of this is to cause calcite to start to precipitate. Calcite
is relatively soft, rating 3 on Moh's hardness scale. This means that
if it was any softer it would be possible to scratch it with a fingernail.
For this reason it is very important that visitors to caves do not touch
the formations as it is very easy to wear the surface away. Although the
usual colour for calcite is white mineral impurities will cause the crystal
to adopt other colours. Yellows, reds and browns are commonly created
due to the presence of muds or concentrations of iron oxide. Touching
calcite allows oils from the skin to penetrate the crystal structure turning
it black. A common mistake is to say that the water hardens. This is incorrect
- afterall hard water would be ice and since the caves are around 17 degrees
Celsius ice formations would quickly melt.
Calcite Flowstone Stalactite Stalagmite Column Shawl Helictite Rimpool
FLOWSTONE
When water enters the cave it must flow somewhere. If the water simply
flows away, over rock or mud, it will leave a trace of calcite crystal
behind. More water deposits more crystal until a hard sheet of crystal
has been created. This is what flowstone is. A simple way of thinking
of it is stone that has flowed down over a surface. Remember that the
stone doesn't really flow - it is just crystal deposits from the water.
If a deposit of flowstone is sparkling it is most likely dry. Light is
able to reflect off the crystal facets quite easily. If the flowstone
has a waxy appearance then it is probably coated in a film of water and
hence new formation is being deposited.
Calcite Flowstone Stalactite Stalagmite Column Shawl Helictite Rimpool
STALACTITES
These are the formations everyone thinks of when they think of caves.
Water seeps through from above and forms a droplet that hangs from the
roof. Carbon dioxide is released fromt he water into the surrounding atmosphere.
The water may evaporate slightly as well. This has the effect of causing
the dissolved calcium carbonate to forms crystals of calcite that are
attahced to the ceiling of the cave. Initially when a stalactite forms
it is like a drinking straw. The crystal has formed around the edge of
the drop of water and continues to do so, forminga tube that hangs down.
Eventually the tube becomes blocked which forces the water to be exuded
through the walls of the stalactite and to run down the outside. When
this happens the stalactite starts to become thicker as well as longer.
Calcite Flowstone Stalactite Stalagmite Column Shawl Helictite Rimpool
STALAGMITES
Water entering the cave drips onto the ground. As it does so a small
amount of crystal is deposited. If the water continues to drip onto the
same spot a crystal deposit is formed which rises upwards. Depending on
such factors as cave climate and drip rate, the stalagmite which is formed
could become thin or relatively thick
Calcite Flowstone Stalactite Stalagmite Column Shawl Helictite Rimpool
COLUMNS
When a stalactite and stalagmite join together so there is a continual
pillar of crystal reaching from the floor to the roof it is known as a
column.
Calcite Flowstone Stalactite Stalagmite Column Shawl Helictite Rimpool
SHAWLS
If the roof of the cave is of a gentle enough slope a drop of water
may run down the wall rather than falling directly onto the floor to form
a stalagmite. Subsequent drops of water follow the same path, with each
droplet of water leaving behind a trace of crystal. Over time a sheet
of crystal, known as a shawl or drapery, is built up.
Calcite Flowstone Stalactite Stalagmite Column Shawl Helictite Rimpool
HELICTITES
For many years these formations were called cave mysteries on account
of their being no explanation of how they formed. Even today many cave
guides will declare that there is no explanation for them. These days
the mechanisms are better understood although they are much harder to
explain than other cave decorations. Helictites form when the water which
feeds them is exuded from the rock sufficiently slow that it does not
form a drop of water. Examination of a helictite unde a microscope reveals
a small hairlike tube a fraction of a millimetre in diameter running through
the centre. Water is drawn through by capillary action and forms a smear
of moisture of the tip. A variety of forces come into play causing the
formation to twist in a variety of directions.
Calcite Flowstone Stalactite Stalagmite Column Shawl Helictite Rimpool
RIMPOOLS
A rimpool forms where there is a pool of water. It may form when the
water becomes saturated with calcium carbonate and forms what appears
to be a scum of crystal. Surface tension draws this to the edge of the
pool where it is deposited. This serves as a centre for crystal to continue
to form which goes on to create what appears to be a dam wall. These walls
are what are known as rimpools. Rimpools can also form where water flows
over a rough surface. Where the water thins there is preferential deposition
of crystal. The crystal starts to build up small walls and so rimpools
are formed.
Calcite Flowstone Stalactite Stalagmite Column Shawl Helictite Rimpool
