Gaylussite
Chemical formula: Na<sub>2</sub>Ca(CO<sub>3</sub>)<sub>2</sub>·5H<sub>2</sub>O
Gaylussite is a hydrated sodium and calcium carbonate, forming characteristic wedge-shaped crystals in saline lakes and evaporitic deposits.
Properties
- Mohs hardness
- 2.5-3
- Luster
- Vitreous
- Streak
- White
- Density
- 1.99
- Cleavage
- Perfect on {001}, distinct on {110}
- Fracture
- Conchoidal
- Transparency
- Transparent to Translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification A key diagnostic feature of gaylussite is its characteristic, sharp-edged, wedge-shaped crystal habit. Low hardness (can be scratched by a copper coin) and density are also helpful. It reacts violently with hydrochloric acid, which is typical for carbonates. ## Distinguishing from Similar Minerals It can be confused with other evaporites, such as trona, thermonatrite, or pirssonite. Pirssonite has a similar composition but crystallizes in the orthorhombic system and has different crystal shapes. Trona and thermonatrite are softer than gaylussite. Verification often requires chemical or crystallographic analysis. ## Crystal Forms Crystals are monoclinic, often pseudo-orthorhombic in habit, flattened, wedge-shaped, or in the form of sharp bipyramids. They often occur as single, well-formed crystals grown on or embedded in soft sediment.
Geological environment
## Genesis Gaylussite is a mineral of evaporitic origin. It forms by precipitation from saline, alkaline lake waters (so-called soda lakes) in an arid, desert climate. It crystallizes directly from solution or in bottom sediments rich in sodium and carbonates. ## Mineral Associations It often co-occurs with other evaporite minerals, such as trona, thermonatrite, pirssonite, northupite, as well as calcite, dolomite, and clay minerals. ## Localities The most important and classic localities for this mineral are salt lakes. Excellent specimens come from Deep Spring Lake and Searles Lake in California (USA) and from Lake Amboseli in Kenya. It also occurs in Lagunillas in Venezuela (type locality), in the Wadi El Natrun valley in Egypt, and in salt lakes in Mongolia and China.
Rarity
Not very common
For collectors
## Quality Criteria The most valued by collectors are large, sharp, transparent, and well-formed crystals with a vitreous luster. Specimens from classic localities, such as Deep Spring Lake, are particularly sought after. The completeness of the crystal, lack of damage, and natural, uncleaned surfaces are also important. Associations with other rare evaporites enhance its appeal. ## Popular Localities The most famous specimens, considered the best in the world, come from Deep Spring Lake in Inyo County, California, USA. Crystals from Searles Lake (California) and Lake Amboseli in Kenya, which yielded large, though often less transparent crystals, are also highly valued.
Care and storage
## Cleaning Gaylussite specimens should only be cleaned dry, using a soft brush to remove dust. Contact with water, especially warm water, causes it to dissolve. Ultrasonic cleaners and steam cleaning should be avoided. ## What to Avoid The mineral is very sensitive to moisture and temperature changes. Heating causes the loss of crystallization water and its decomposition. It should be protected from direct sunlight, which can heat it. It is also sensitive to acids, with which it reacts violently, releasing carbon dioxide. ## Storage Gaylussite requires storage under stable conditions, in a dry environment. It is best kept in closed, airtight containers (e.g., "membrane boxes") or in cabinets with a desiccant to prevent its slow decomposition. It should be isolated from specimens that may release moisture.