Geology Reference
In-Depth Information
Plate 8.17
Straw stalactites, Ogof Capel, Clydach, South Wales.
(
Photograph by Clive Westlake
)
but was unaffected by the drip rate (Genty
et al
. 2001).
One site in the Grotte de Clamouse, which has little soil
cover, failed to display a correlation between stalagmite
growth rate and temperature, either because little carbon
dioxide was produced in the thin soil or because calcite
was precipitated before entering the system.
Water trickling down sloping walls or under a taper-
ing stalactite produces
draperies
(curtains and shawls),
which may be a single crystal thick (Colour Plate 7,
inserted between pages 208 and 209). Varieties with
coloured bands are called 'bacon'.
Flowstone sheets
are
general sheets of flowstone laid down over walls and
ceilings.
grapes. They are a variety of
coralloid forms
, which are
nodular and globular and look like coral.
Anthodites
are gypsum clusters that radiate from a central point.
Moonmilk
or
rockmilk
is a soft, white, plastic, moist
form of calcite, and often shaped like a cauliflower.
Sub-aqueous forms
Sub-aqueous forms are rimstone pools, concretions, pool
deposits, and crystal linings.
Rimstone pools
form
behind
rimstone dams
, sometimes called
gours
, which
build up in channels or on flowstones (Colour Plate 8,
inserted between pages 208 and 209). In rimstone pools,
a suite of deposits precipitates from supersaturated mete-
oric water flowing over the outflow rim and builds a
rimstone dam.
Pool deposits
are any sediment or crys-
talline deposits in a cave pool.
Crystal linings
are made
of well-formed crystals and are found in cave pools with
little or no overflow.
Pisoliths
or
cave pearls
are small balls, ranging from
about 0.2 mm to 15 mm in diameter, formed by regular
accretions of calcite about a nucleus such as a sand grain
(Colour Plate 9, inserted between pages 208 and 209).
A few to thousands may grow in shallow pools that are
agitated by drops of feedwater.
Eccentric forms
Eccentric
or
erratic
forms, which are speleothems of
abnormal shape or attitude, include shields, helictites,
botryoidal forms, anthodites, and moonmilk.
Shields
or
palettes
are made of two parallel plates with a small cavity
between them through which water seeps. They grow up
to5mindiameter and 4-10 cm thick.
Helictites
change
their axis from the vertical during their growth, appearing
to disobey gravity, to give a curving or angular, twig-like
form (Plate 8.18).
Botryoidal forms
resemble bunches of
