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a mineral, orthorhombic calcium carbonate, CaCO 3 , chemically identical with calcite but differing in crystallization and in having a higher specific gravity and less marked cleavage.
Historical Examples

aragonite is the least stable form; crystals have been found altered to calcite.
Encyclopaedia Britannica, 11th Edition, Volume 4, Part 4 Various

aragonite, a mineral formed of calcium carbonate crystallized in the rhombic system; specific gravity 2.94 (compare Calcite).
The New Gresham Encyclopedia. Vol. 1 Part 2 Various

Many limestones are rich in aragonite, but this in course of time tends to recrystallize as calcite.
Encyclopaedia Britannica, 11th Edition, Volume 8, Slice 6 Various

aragonite is the more unstable of the two modifications of calcium carbonate.
Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 Various

Like aragonite it is very frequently twinned, the compound crystals being pseudo-hexagonal in form.
Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 7 Various

The thermal springs of Carlsbad deposit spherical concretions of aragonite, forming masses known as pisolite or Sprudelstein.
Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3 Various

Many calcareous fragments consist of aragonite, wholly or principally, and this mineral tends to be replaced by calcite.
Encyclopaedia Britannica, 11th Edition, Volume 16, Slice 6 Various

aragonite occurs in very small masses, of a light yellow color and fibrous structure, between layers of serpentine.
Scientific American Supplement, No. 415, December 15, 1883 Various

Thus calc spar is a common name for calcite, heavy spar for barite, needle spar for aragonite, and so on.
Birds and Nature, Vol. 12 No. 2 [July 1902] Various

Being isomorphous with aragonite, it crystallizes in the orthorhombic system, but simple crystals are not known.
Encyclopaedia Britannica, 11th Edition, Volume 4, Part 3 Various

noun
a generally white or grey mineral, found in sedimentary rocks and as deposits from hot springs. Composition: calcium carbonate. Formula: CaCO3. Crystal structure: orthorhombic
aragonite
(ə-rāg’ə-nīt’, ār’ə-gə-)
A usually white, yellowish, or pink orthorhombic mineral that can occur in many different colors. Aragonite occurs as acicular (needlelike) or tabular crystals, or as fibrous aggregates. It is found in gypsum deposits, at the tips of calcite crystals, in mollusk shells and pearls, and in living reef structures. It is a polymorph of calcite. Chemical formula: CaCO3.