Macraeite

Chemical formula: K(H<sub>2</sub>O)Mn<sup>2+</sup><sub>2</sub>(Fe<sup>3+</sup><sub>2</sub>Ti<sup>4+</sup>)(PO<sub>4</sub>)<sub>4</sub>[O(OH)](H<sub>2</sub>O)<sub>10</sub>·4H<sub>2</sub>O

Macraeite is a rare, hydrated phosphate of potassium, manganese, iron, and titanium, forming microscopic, bladed crystals of a brown color.

## Characteristics Macraeite is a mineral from the phosphate group, characterized by a complex chemical composition including potassium, manganese, iron, and titanium. It occurs as very small, bladed or acicular crystals, rarely exceeding 0.2 mm in length. These crystals form rosette-like or radial aggregates, and also protrude from the surfaces of vugs in the host rock. Due to its small size, its visual features are difficult to observe without magnification. ## Physical Properties Macraeite crystals are flexible and exhibit brown pleochroism. The luster is described as vitreous to silky. Hardness and density have not been precisely measured due to the small size and delicacy of the crystals. ## Colors and Varieties This mineral has a characteristic brown color in various shades. No varieties have been distinguished. ## History and Name Macraeite was approved as a new mineral by the International Mineralogical Association (IMA) in 2022. Its name honors Canadian mineral collector and researcher, Ian MacRae, for his contributions to mineralogy, including the discovery of several new mineral species at the Francon quarry in Montreal. The type specimen, on which the mineral was described, was collected at this very location. ## Uses Macraeite has no industrial application. It is solely an object of scientific and collecting interest as a very rare mineralogical species.

Properties

Luster
Vitreous to silky
Streak
Light brown
Cleavage
Good on {010}
Fracture
Uneven
Transparency
Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Amateur identification of macraeite is practically impossible. It requires specialized analytical methods, such as Raman spectroscopy or chemical analysis using an electron microprobe (EDS/WDS). A characteristic feature in laboratory studies is its unique chemical composition. ## Distinguishing from Similar Minerals It can be confused with other fine-grained phosphates or oxides occurring in similar environments, such as strengite, rockbridgeite, or cacoxenite. Differentiation is based solely on advanced instrumental analyses. ## Crystal Forms Macraeite forms very small, elongated crystals with a bladed or acicular habit. These crystals often arrange themselves into radial or rosette-like aggregates, growing from voids in the rock.

Geological environment

## Genesis Macraeite is a secondary mineral that formed as a result of hydrothermal processes occurring in the late stage of crystallization within a nepheline syenite. It crystallizes in small rock cavities and fissures (miarolitic cavities). ## Mineral Associations This mineral co-occurs with other rare minerals found in the Francon quarry. The most important associated minerals include: weloganite, dawsonite, quartz, analcime, microcline, aegirine, catapleiite, and dresserite. ## Localities The only confirmed locality of macraeite in the world is its type locality - the Francon quarry in Montreal, Quebec, Canada. This is a famous mineralogical site, known for the occurrence of many rare and unique alkaline minerals.

Rarity

Extremely rare

For collectors

## Quality Criteria As a "micromount" type mineral, the collector's value of a specimen depends on the richness and aesthetics of the crystal aggregates, as well as their association with other rare minerals from this locality. The most desirable specimens are those with clearly formed, undamaged crystal rosettes, contrasting well with the host rock. ## Popular Localities All known specimens come exclusively from the Francon quarry in Montreal (Quebec, Canada), which is currently inactive and inaccessible to collectors. Material for research and collections comes from old collections.

Care and storage

## Cleaning Macraeite specimens are extremely delicate and susceptible to mechanical damage. Cleaning is not recommended. Any attempts to remove dust should be limited to very careful use of a soft brush or a photographic air blower, without touching the crystals. ## What to Avoid Contact with water, chemicals, ultrasound, and sudden temperature changes must be strictly avoided. The mineral is hydrated, so heating can lead to its permanent damage. Due to the flexibility of the crystals, any pressure should be avoided. ## Storage Specimens should be stored under stable conditions, in sealed "micromount" containers, to protect them from dust, moisture, and physical damage. They should not be exposed to direct sunlight.

Sources

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