Ferrotychite

Chemical formula: Na<sub>6</sub>Fe<sup>2+</sup><sub>2</sub>(CO<sub>3</sub>)<sub>4</sub>(S<sup>6+</sup>O<sub>4</sub>)

Ferrotychite is a rare, colorless or pale yellow carbonate and sulfate of sodium and iron, forming small, vitreous crystals with a regular system.

## Characteristics Ferrotychite is a complex mineral from the carbonate and sulfate group, belonging to the northupite group. It occurs as small, well-formed, octahedral crystals, less frequently as granular aggregates. Crystals are usually small, reaching up to 2 mm in size. It is a brittle mineral. ## Physical Properties It is characterized by a hardness of 4 on the Mohs scale and a density of approximately 2.63 g/cm³. It has a distinct, vitreous luster. It is transparent to translucent. It does not exhibit fluorescence under ultraviolet light. ## Colors and Varieties Ferrotychite is usually colorless, white, or pale yellow. No colored varieties or trade names are known. ## History and Name The mineral was first described in 1981 by G.Y. Chao, Judith G. Fitzpatrick, and Joan J. Gill. Its name refers to its chemical composition – it contains iron (Latin: *ferrum*) – and its structural similarity to tychite. ## Uses Ferrotychite has no industrial application. Due to its rarity and small crystal size, it is a mineral of interest mainly to collectors specializing in rare mineral species and to scientists.

Properties

Mohs hardness
4
Luster
Vitreous
Streak
White
Density
2.63
Cleavage
Imperfect on {111}
Fracture
Conchoidal
Transparency
Transparent to translucent
Crystal system
Cubic

Diagnostic features

## Identification Ferrotychite is most easily recognized by its characteristic octahedral crystal form and vitreous luster. A key diagnostic feature is its reaction to water and acids – it dissolves in them. Its occurrence in a specific geological environment (alkaline intrusions) is also an important clue. ## Distinguishing from Similar Minerals It can be confused with structurally similar tychite (Na₆Mg₂(CO₃)₄SO₄), which contains magnesium instead of iron. Distinguishing these two minerals without advanced chemical analyses (e.g., EDS) is practically impossible. Other similar minerals from the same locality, such as northupite or bradleyite, also require specialized studies for certain identification. ## Crystal Forms Ferrotychite crystals most often take the form of regular octahedra {111}, sometimes with small cube faces {100}. They occur as single, overgrown crystals or inclusions in other minerals.

Geological environment

## Genesis Ferrotychite is a hydrothermal mineral, crystallizing in the late stages of the formation of complex alkaline intrusions and carbonatites. It forms in rock caverns and vugs. ## Mineral Associations This mineral co-occurs with other rare alkaline minerals. In its type locality (Mont Saint-Hilaire), it was found in association with trona, northupite, tychite, shortite, eitelite, bradleyite, analcime, microcline, and aegirine. ## Localities The only confirmed and thoroughly described occurrence of ferrotychite in the world is the Poudrette quarry at Mont Saint-Hilaire in Quebec, Canada. This is its type locality.

Rarity

Very rare

For collectors

## Quality Criteria The most valuable ferrotychite specimens are those with sharp, well-formed, transparent, and lustrous crystals that are clearly exposed on the rock matrix. Due to the small size of the crystals (usually less than 2 mm), size is a key factor influencing value. Contrast with associated minerals also enhances the attractiveness of the specimen. ## Popular Localities The only source of collector specimens is the Poudrette quarry at Mont Saint-Hilaire in Canada, which is known for the occurrence of many rare and unique alkaline minerals.

Care and storage

## Cleaning Cleaning with compressed air or a very soft brush is recommended. The mineral is soluble in water and acids, so all contact with liquids should be avoided. ## What to Avoid Contact with water (both cold and hot), water vapor, and all chemical agents, including acids, which decompose it, must be absolutely avoided. It should be protected from moisture and high temperatures. ## Storage Ferrotychite specimens should be stored in a dry place, preferably in a sealed, closable display box or container with a desiccant, to prevent its slow decomposition due to atmospheric moisture.

Sources

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