Aragonite

Aragonite is a polymorph of calcite. In hand sample, it can be distinguished from calcite by its lack of rhombohedral cleavage and, in sufficiently translucent samples, its lack of double refraction.

Physical Properties
Chemical formula CaCO3
Class Carbonate
Crystal system Orthorhombic
Habit Acicular
Tabular
Prismatic
Fibrous
Radiating splays
Crusts
Masses of different morphologies
Color Colorless to white
Pale yellow
Grey
White
Brown
Red
Pink
Purple
Orange
Blue
Green
Hardness 3.5 to 4
Specific gravity 2.94
Cleavage Good (010), poor {110}
Fracture Subconchoidal
Luster Vitreous
Transparency Transparent to translucent
Streak White
Optical Properties
PPL Colorless, but may exhibit pale pastels
High relief
XPL Extremely high birefringence
colors may look pastel, washed out,
or almost neon
High reliefParallel extinction
δ 0.155
Twinning Contact
Cyclic
May appear pseudohexagonal
Extinction Parallel
Special properties
Reacts with HCl (fizzes)
after Perkins, 386

Aragonite in Hand Sample

Aragonite

Obverse of the above sample

Aragonite with right-angle twinning

Aragonite in Thin Section

Stay tuned!

Further Reading

Aragonite at webmineral.com

Aragonite at mindat.org