Görgeyite
Chemical formula: K₂Ca₅(S⁶⁺O₄)₆·H₂O
Görgeyite is a rare, hydrated potassium calcium sulfate, forming colorless or white, tabular crystals with a vitreous luster.
Properties
- Mohs hardness
- 3.5
- Color
- Colorless, white, pale yellow, greenish yellow
- Luster
- Vitreous
- Streak
- (not reported)
- Density
- 2.90
- Cleavage
- Distinct on {100}
- Fracture
- Splintery,Hackly
- Transparency
- Translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification The key diagnostic feature of görgeyite is its tabular crystal habit, perfect cleavage in one direction, and pearly luster on cleavage planes. The reaction to water (solubility) is also a characteristic, though destructive, feature. The mineral is relatively soft (3.5 on the Mohs scale). ## Distinguishing from Similar Minerals It can be confused with other colorless sulfates found in evaporites, such as gypsum, anhydrite, or polyhalite. It differs from gypsum by its greater hardness and crystal habit. It differs from anhydrite by the presence of water in its structure and lower hardness. Polyhalite usually forms fibrous or massive aggregates and has a slightly different hardness. ## Crystal Forms Görgeyite crystals are tabular, often with hexagonal or octagonal outlines. They usually occur in radial or fan-shaped aggregates, as well as single, overgrown crystals in salt rock fissures.
Geological environment
## Genesis It is an evaporitic mineral, forming in the final stages of crystallization in salt basins. It forms as a result of hydrothermal activity or diagenetic processes in rock salt and potash-magnesium deposits. It forms in an environment rich in potassium and calcium. ## Mineral Associations It most often co-occurs with other salt minerals, such as halite, anhydrite, polyhalite, kainite, sylvite, gypsum, and less frequently with leonite and bloedite. ## Localities The most important localities worldwide include salt deposits in Austria (Bad Ischl - type locality, Hallstatt), Germany (potash deposit in Lower Saxony), and also in the USA (potash deposits in New Mexico, in the Permian Basin). Occurrences have also been reported in Italy (Sicily) and Kazakhstan.
Rarity
Rare
For collectors
## Quality Criteria The most valued specimens by collectors are those with well-formed, sharp, and transparent crystals, forming aesthetic, radial aggregates. Crystal size is important – larger ones are rarer and more desirable. A contrasting matrix, e.g., of halite, enhances the specimen's attractiveness. Purity (lack of inclusions) and absence of mechanical damage are crucial for value. ## Popular Localities Classic and most valued specimens come from historical localities in Austria, such as Bad Ischl and Hallstatt. Specimens from German potash mines are also known in the collector's market.
Care and storage
## Cleaning Görgeyite specimens should be cleaned only dry, using a soft brush to remove dust. The mineral is water-soluble, so contact with water, especially hot water, is absolutely inadvisable and leads to its destruction. ## What to Avoid Avoid all contact with water and other liquids. The mineral is sensitive to atmospheric moisture, which can cause its slow degradation. It should be protected from high temperatures and direct sunlight. ## Storage It is recommended to store specimens in a dry place, preferably in tightly sealed containers or display cases with a moisture absorber (e.g., silica gel). Display should be in closed showcases, away from sources of moisture and heat.