Alabaster

Alabaster is named after its supposed early source at Alabaston, a town in Egypt.

Alabaster is the massive variety of Gypsum, which can occur as transparent crystals often twinned in swallow-tailed forms. The purest form of alabaster is white and translucent but the impurities (e.g. ferric oxide) can colour the stone in yellows, browns and black in veins or patches.

Alabaster has been used as an ornamental stone for a long time.
General Information
A variety or type of:Gypsum
Chemical Formula
CaSO
 
4
· 2H
 
2
O
Walter Schumann, Gemstones of the world (2001)
Photos of natural/un-cut material from mindat.org
Alabaster Treatments
Webster (p.298) reports that carved alabaster objects are often immersed in cold water, the temperature of which is slowly raised to boiling and then again slowly cooled; these changes are the appearance of the alabaster so that it looks more like the much harder white marble. Heating may 'open pores' or produce cracks which permit better penetration of dyes.
Dyeing and colored oiling have often been used to make alabaster more attractive and, for example, to distinguish the two colors in chess boards and in carved chess pieces. Carbed objects are also often waxed and may be coated with paint when in statue form - Nassau (1984)
Physical Properties of Alabaster
Mohs Hardness2
Walter Schumann, Gemstones of the world (2001)
More from other references
Specific Gravity2.30 to 2.33
Michael O’Donoghue, Gems, Sixth edition (2006)
Cleavage QualityGood
Michael O’Donoghue, Gems, Sixth edition (2006)
Optical Properties of Alabaster
Refractive Index1.520 to 1.530
Walter Schumann, Gemstones of the world (2001)
More from other references
Birefringence+0.010
Walter Schumann, Gemstones of the world (2001)
DispersionNone
Walter Schumann, Gemstones of the world (2001)
Colour
Colour (General)White, pink, brownish.
Walter Schumann, Gemstones of the world (2001)
More from other references
TransparencyTranslucent,Opaque
Walter Schumann, Gemstones of the world (2001) Translucent at edgesMore from other references
Fluorescence & other light emissions
Fluorescence (General)Usually a brownish shade
Michael O’Donoghue, Gems, Sixth edition (2006)
Crystallography of Alabaster
Crystal SystemMonoclinic
Michael O’Donoghue, Gems, Sixth edition (2006)
HabitMassive
Michael O’Donoghue, Gems, Sixth edition (2006)
Geological Environment
Where found:It may be formed in mineral veins where sulphuric acid, derived from the oxidation of pyrite and other sulphides, has acted upon limestone.
Michael O’Donoghue, Gems, Sixth edition (2006)
Further Information
Mineral information:Alabaster information at mindat.org
Significant Gem Localities
Italy
 
  • Tuscany
    • Pisa Province
      • Castellina Marittima
        • Marmolaio Valley
          • Pomaia
Gems, Sixth Edition, Michael O’Donoghue , 2006, p. 378
Peru
 
  • Amazonas
UK
 
  • England
    • Derby
Gems, Sixth Edition, Michael O’Donoghue , 2006, p. 379
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