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 the more unstable of the two modifications of calcium carbonate.
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 presence of aragonite and dolomite in the shales suggests that at least some of the carbonate deposition might well have been because of excessive evaporation and high concentrations of carbonates (Smith 1974, pers.
In the first place, it should be understood that both conchiolin and aragonite are translucent, that is, they pass light to a certain extent.
On observing it under polarized light the calcareous substance is discovered to be everywhere crystallized, and this suggests the question whether the carbonate has here taken the form ofaragonite or of calcite.
It is probable that if the operation were to take place under the influence of heat, under the conditions above mentioned, aragonite would be formed.
In the animal kingdom it occurs as both calcite and aragonite in the tests of the foraminifera, echinoderms, brachiopoda, and mollusca; also in the skeletons of sponges and corals.
Aragonite is the least stable form; crystals have been found altered to calcite.
It constitutes the bulk of the chalk deposits and limestone rocks; it forms over one-half of the mineral dolomite and the rock magnesium limestone; it occurs also as the dimorphous minerals aragonite (q.
Chemically, calcite has the same composition as the orthorhombic aragonite (q.
A kind of pseudomorph, in which there has been a change of physical characters without alteration of chemical composition, as the change of aragonite to calcite.
When twinned on the prism planes o, as is frequently the case, the crystals simulate hexagonal symmetry still more closely, as in the minerals aragonite and chrysoberyl.
Pseudomorphs after calcite are known; and it is notable that native copper occurs pseudomorphous after aragonite at Corocoro, in Bolivia, where the copper is disseminated through sandstone.
As aragonite is always formed from hot solutions, it appears that dilution with water acts like heat.
Rose's observation on the formation (by the slow diffusion of solutions of calcium chloride and sodium carbonate) of aragonite from dilute, and of calc spar from strong, solutions is easily understood from this point of view.
It may therefore be supposed that calc spar presents the form corresponding with a low temperature, and aragonite with a higher temperature during crystallisation.
Pop-corn, therefore, is the globular aragonite of the stalagmitic variety.
In all cases the original box work has been in thin sheets of calcite, and the heavy varieties are due to later deposits of calcite and aragonite crystals or, pop corn.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "aragonite" in a variety of sentences. We hope that you will now be able to make sentences using this word.
