Meridianiite
Chemical formula: MgS<sup>6+</sup>O<sub>4</sub>·11H<sub>2</sub>O
Meridianite is a hydrated magnesium sulfate that is stable only at low temperatures (below 2°C) and was originally identified on Mars.
Description
## Characteristics Meridianite is a sulfate mineral, specifically magnesium sulfate undecahydrate (MgSO₄·11H₂O). Its most characteristic feature is its instability under room temperature conditions. It is stable only at temperatures below approximately 2°C. Above this limit, it thermally decomposes, losing some of its crystallization water and transforming into epsomite (MgSO₄·7H₂O), which forms white, powdery coatings on the surface of crystals. Meridianite specimens are typically colorless and transparent. It forms acicular or bladed crystals, which can be aggregated into radiating clusters. ## Physical Properties This mineral is very soft and brittle. It has a vitreous luster and is completely transparent when fresh. Its density is approximately 1.52 g/cm³, making it a very light mineral. It is readily soluble in water. ## Colors and Varieties Meridianite is colorless. No colored varieties or trade names are distinguished. ## History and Name The mineral's name, approved in 2007, comes from its initial identification location – Meridiani Planum on Mars, where its presence was inferred from data collected by the Opportunity rover. On Earth, it was later identified in salt lake sediments and ice cores, confirming its natural existence. The terrestrial type locality is at Paonga Lake in British Columbia (Canada). ## Applications Meridianite has no industrial applications. Its significance is purely scientific, as an indicator of specific, low-temperature conditions for the formation of evaporite deposits, both on Earth and on other planets.
Diagnostic features
## Identification The most important diagnostic feature of meridianite is its behavior at room temperature. A freshly extracted, transparent crystal begins to become cloudy and covered with a white, powdery coating (epsomite) after a short time, which is a result of its decomposition. This feature allows for its quick identification. Additionally, it is very light and dissolves in water. ## Distinguishing from Similar Minerals Meridianite can be confused with other hydrated sulfates, such as epsomite or mirabilite. It is distinguished from epsomite by its thermal instability – epsomite is stable at room temperature. Mirabilite (sodium sulfate) is also unstable and easily effloresces, but has a different chemical composition. In natural conditions (below freezing), it can be confused with ice, from which it is distinguished by its crystalline form and slightly higher density. ## Crystal Forms Meridianite crystallizes in elongated, acicular or flattened, bladed crystals. It often forms radiating or chaotically arranged aggregates.
Geological environment
## Genesis Meridianite is an evaporite mineral, crystallizing from highly saline solutions (brines) rich in magnesium sulfate under very low temperatures, below 2°C. It forms in seasonally freezing salt lakes, brine inclusions in sea ice, and ice cores. ## Mineral Associations On Earth, meridianite coexists with other evaporite minerals, such as epsomite (often as a decomposition product), mirabilite, halite, and gypsum. ## Localities Confirmed occurrences on Earth include salt lakes in Canada (Paonga Lake, British Columbia), Spain (Basque Country), and Iran. It has also been found in ice cores from Antarctica (Vostok Station) and Greenland. Its type locality, however, is Meridiani Planum on Mars.
Rarity
Very rare
Collector aspects
## Quality Criteria Due to the nature of the mineral, the main criterion for collectible value is the mere possession of a properly preserved specimen. The most highly valued are transparent, well-formed acicular crystals or their aggregates, preserved in their original form (without signs of decomposition). The size of the crystals is rarely large, so even small but well-formed specimens are valuable. Specimens from well-documented scientific finds have additional value. ## Popular Localities Collectible specimens mainly come from several salt lakes, primarily from localities in British Columbia, Canada, and Spain. However, they are extremely difficult to obtain and preserve, which means they are almost exclusively found in institutional collections and among highly specialized private collectors.
Care and storage
## Cleaning Meridianite specimens should not be cleaned wet, as the mineral is soluble in water. Mechanical cleaning, even with a soft brush, is very risky due to its extreme brittleness. It is safest to leave the specimen uncleaned. ## What to Avoid The greatest threat to meridianite is temperatures above 2°C, which cause its irreversible decomposition into epsomite and water. Heating, or even exposure to room temperature, must be strictly avoided. The mineral is also sensitive to low air humidity, which accelerates its dehydration. Contact with water or any other liquid leads to its dissolution. ## Storage Meridianite requires specialized storage conditions. Specimens must be kept in hermetically sealed containers under refrigeration or freezing conditions (at a constant temperature below 2°C). Only such handling guarantees the preservation of their original form. It is not suitable for display under typical collecting conditions.