ous in character.

[Illustration: FIG. 1.]

[Illustration: FIG. 2.]

The mineral was first found, as reddish twinned crystals with the form
of six-sided prisms, at Molina in Aragon, Spain, where it occurs with
gypsum and small crystals of ferruginous quartz in a red clay. It is
from this locality that the mineral takes its name, which was originally
spelt arragonite. Fine groups of crystals of the same habit are found in
the sulphur deposits of Girgenti in Sicily; also at Herrengrund near
Neusohl in Hungary. At many other localities the mineral takes the form
of radiating groups of acicular crystals, such as those from the
haematite mines of west Cumberland: beautiful feathery forms have been
found in a limestone cave in the Transvaal. Fibrous forms are also
common. A peculiar coralloidal variety known as _flosferri_ ("flower of
iron") consists of radially arranged fibres: magnificent snow-white
specimens of this variety have long been known from the iron mines of
Eisenetz in Styria. The calcareous secretions of many groups of
invertebrate animals consist of aragonite (calcite is also common);
pearls may be specially cited as an example.

Aragonite is a member of the isomorphous group of minerals comprising
witherite (BaCO3), strontianite (SrCO3), cerussite (PbCO3) and bromlite
((Ba, Ca)CO3); and crystals of aragonite sometimes contain small amounts
of strontium or lead. A variety known as tarnowitzite, from Tarnowitz in
Silesia, contains about 5% of lead carbonate.

Aragonite is the more unstable of the two modifications of calcium
carbonate. A crystal of aragonite when heated becomes converted into a
granular aggregate of calcite individuals: altered crystals of this kind
(paramorphs) are not infrequently met with in nature, whilst in fossil
shells the original nacreous layer of aragonite has invariably been
altered to calcite. From a solution of calcium carbonate in water
containing carbon dioxide crystals of calcite are deposited at the
ordinary temperature, but from a warm solution aragonite crystallizes
out. The thermal springs of Carlsbad deposit spherical concretions of
aragonite, forming masses known as pisolite or _Sprudelstein_.
(L. J. S.)

ARAGUA, one of the smaller states of Venezuela under the redivision of
1904, lying principally within the parallel ranges of the Venezuelan
Cordillera, and comprising some of the most fertile and healthful
valleys of the republic. It is bounded E. by the