Gaylussite is a relatively rare mineral but a very rare gem. It is one of several carbonate minerals that form in non-marine evaporite deposits. These carbonates include Trona, Pirssonite, Nahcolite, Northupite and Thermonatrite and are difficult to tell apart from each other. Optical or X-ray techniques are often necessary to identify them. Gaylussite is subject to dehydration which can cause cloudiness of gems and deterioration and therefore should be stored in a sealed container.

Notable occurrences include Searles Lake, San Berardino County; Deep Spring and Owens Lake, Inyo County; Borax Lake, Lake County and China Lake, Kern County, California, USA; Gobi Desert, Mongolia and Lagunillas, Merida, Venezuela.

Category: Carbonate mineral
Chemical Formula: Na2Ca(CO3)2·5(H2O)
  Hydrated Sodium Calcium Carbonate
Molecular Weight: 296.15 gm
Composition: Sodium 15.53 % Na 20.93 % Na2O
Calcium 13.53 % Ca 18.94 % CaO
Hydrogen 3.40 % H 30.42 % H2O
Carbon 8.11 % C 29.72 % CO2
Oxygen 59.43 % O    
  100.00 % 100.00 % = TOTAL OXIDE


Crystallography: Monoclinic – Prismatic
Crystal Habit: Includes intricately faceted prismatic to tabular crystals, but also massive and encrusting. Crystals frequently elongated [100]; also flattened, wedge-shaped, with dominant [110], and [011]. Surfaces commonly rough, with [011] striated [111].
Twinning: None


Cleavage: [110] Perfect, [001] Imperfect
Fracture: Conchoidal
Tenacity: Very Brittle
Moh’s Hardness: 2.5 – 3.0
Density: 1.93 – 1.99 (g/cm3)
Luminescence: None
Radioactivity: Not Radioactive
Other: Dehydrates slowly with efflorescence in dry air; slowly decomposes in water leaving CaCO3 as Calcite or Aragonite. Soluble in acids with effervescence. Slightly soluble in water. Alters readily to calcite.


Color: Colourless, Yellowish, Greyish, White; Colourless in transmitted light.
Transparency: Transparent to Translucent
Luster: Vitreous
Refractive Index: 1.444 – 1.523  Biaxial ( – )
Birefringence: 0.0790
Dispersion: Strong; r < v
Pleochroism: None