What is Moonstone?
Moonstone is prized for adularescence: a soft blue or white glow that seems to move below the surface. The effect is a structural story of feldspar intergrowth, so cut orientation and natural clarity matter as much as body colour.
Mineralogy and crystal structure
Reference formula: KAlSi3O8. Moonstone is a gem trade name for feldspar showing adularescence, usually involving intergrowths or exsolution between feldspar compositions. The structure shown is an adularia/orthoclase representative model, not a claim that every moonstone has one composition. Moonstone is classified with silicates and has a monoclinic crystal system. Typical hardness is 6–6.5 on the Mohs scale and specific gravity is approximately 2.5–2.6.
Colour, lustre and habit
Typical colours include colourless, white, blue, peach, grey. The usual tabular, prismatic, granular habit and vitreous, pearly lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Moonstone forms in or is associated with feldspar-rich granites, pegmatites and high-temperature to low-temperature feldspar exsolution histories. Important documented localities include Sri Lanka, India, Madagascar, Tanzania, Myanmar, Australia and the United States.
A floating blue sheen in feldspar
Moonstone is prized for adularescence: a soft blue or white glow that seems to move below the surface. The effect is a structural story of feldspar intergrowth, so cut orientation and natural clarity matter as much as body colour.
Collecting and care
Good jewellery hardness but perfect feldspar cleavage; avoid sharp impact, thermal shock and harsh cleaners.
