Gaylussite
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 |
| CLASSIFICATION | |
| Dana (8th edition) : |
15.02.02.01 |
| (15) Hydrated Carbonates | |
| (15.02) where A+m B++n (XO3)p · x(H2O), (m+n):p > 1:1 | |
| (15.02.02) | |
| Nickel-Strunz (10th edition) : |
05.CB.35 |
| (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)