Mineral Information and Data:

Na2Ca(CO3)2 • 5H2O [CNMNC approved formula]

Named after the French chemist and physicist, Joseph Louis Gay-Lussac (1778-1850).

IMA status : Valid species (Pre-IMA 1826) Grandfathered
(8th edition) :  
  (15) Hydrated Carbonates
  (15.02) where A+m B++n (XO3)p · x(H2O), (m+n):p > 1:1
(10th edition) :
  (05) Carbonates and Nitrates
  (05.C) Carbonates without Additional Anions, with H2O
  (05.CB) With large cations (alkali and alkali-earth carbonates)
Crystal system: Monoclinic System
Point group (H-M): 2/m — prismatic
Space group: C2/c
Unit cell: a = 11.589Ǻ, b = 7.780Ǻ, c = 11.207Ǻ, β = 102.5(1)°, Z=4
Crystal Habit: As flattened wedge-shaped crystals with dominant {110}, {011}, {001}, smaller {010}, {100}, {101}, {112}; also as prismatic to dipyramidal crystals elongated along [100], to 6 cm.
Color: Colorless to pale yellow or pale gray, white; colorless in transmitted light
Diaphaneity: Transparent to translucent
Luster: Vitreous
Hardness (Mohs): 2.5 - 3
Measured Density: 1.991 g/cm3
Cleavage: On {110}, perfect; on {001}, imperfect
Tenacity: Very brittle
Fracture: Conchoidal
Streak: White to pale gray
Geologic Setting: Typically in evaporites or shales from alkali lakes; rarely in veinlets cutting alkalic igneous rocks.
Mineral Association: Shortite, northupite, pirssonite, trona (Green River Formation, Wyoming, USA); thermonatrite, shortite, villiaumite, ferrian “biotite”, pectolite, potassian feldspar, aegirine (Khibiny massif, Russia)
Other Properties: H2O Soluble. Gemstone Extremely Rare.
Comments: Dehydrates with efflorescence in dry air; slowly decomposes in H2O leaving CaCO3 as calcite or aragonite.


Origin: Seales Lake, San Bernadino Co., California, U.S.A.
Sample size: 3.6 x 1.8 x 1.3 cm
Photo: Rob Lavinsky


(another view of above)