Aragonite and the more common mineral Calcite
to each other. Although Aragonite and Calcite contain the same chemical composition
, they differ in crystal structure
. Aragonite forms orthorhombic
crystals, whereas Calcite forms
crystals. Sometimes the crystals of Aragonite and Calcite are too small
to be detected, and it is only possible to distinguish these two
minerals by complex scientific optical
tests. Since the true
identity of microcrystalline
forms of Aragonite or Calcite may not be
known, they may be mislabeled as the wrong mineral.
Almost all Aragonite crystals are twinned
growths of three
individual crystals that form pseudohexagonal trilling
Therefore, although Aragonite crystallizes in the orthorhombic
system, virtually all its crystals are hexagonal
s can be noted from the basal striations
on each of
the three individual crystals running in different directions, causing
a hexagonal crystal to have three striation directions on each base.
Other minerals frequently pseudomorph
commonly pseudomorphs after Aragonite, and although it contains the same chemical composition
and crystal forms as Aragonite, it is really Calcite. There are many Aragonite crystals sold to collectors that are in fact really Calcite pseudomorphs after Aragonite. A rare but popular pseudomorph of Copper
after Aragonite comes from Corocoro, Bolivia.
Aragonite frequently contains sand inclusion
s, which give a
specimen a brown color. It forms in many environments
, but a
particularly interesting one is its formation from deposition of hot,
mineral-rich springs. The water releases the calcium it contains upon
reaching the air, and forms mounds and thick crusts around the springs.
When these deposited mounds and crusts are banded
, they are
sometimes carved and termed "Onyx Marble", "Suisan Marble", "California
Onyx", or "Mexican Onyx".
Aragonite is the main component of many organic
substances, such as
. The iridescent surface of pearl and
is a layer of Aragonite secreted by mollusk
Some forms of Aragonite, especially the Flos Ferri
variety, are very brittle and fragile and may easily break when touched. Such specimens need to be handled with utmost care to preserve them.