Groatite

Chemical formula: &#9744;NaCaMn<sup>2+</sup><sub>2</sub>(PO<sub>4</sub>)(HPO<sub>4</sub>)<sub>2</sub>

Groatite is a very rare, triclinic sodium, calcium, and manganese phosphate, forming small, tabular, brown crystals.

## Characteristics Groatite is a mineral from the phosphate group, chemically classified as a sodium, calcium, and manganese hydrogen phosphate. It occurs as very fine, individual crystals not exceeding 0.5 mm in size. The crystals are most often tabular or platy and exhibit a brown color and vitreous luster. ## Physical Properties The mineral is characterized by a hardness of approximately 3.5 on the Mohs scale. Its crystals are transparent to translucent. It exhibits perfect cleavage in one direction. The streak is light brown. ## Colors and Varieties Groatite occurs in shades of brown. Due to its extreme rarity and occurrence only in microscopic crystals, no color or commercial varieties are distinguished. ## History and Name The mineral is named in honor of LaCathryn A. Groat, a professor in the Department of Earth and Ocean Sciences at the University of British Columbia, Canada, for her contributions to mineralogy. Groatite was approved as a new mineral by the International Mineralogical Association (IMA) in 2008 (IMA2008-049). It was described based on material from its only known locality. ## Uses Groatite, as an extremely rare mineral occurring in microscopic crystals, has no commercial or industrial applications. It is of purely scientific significance and is an object of interest for specialized collectors of rare minerals (so-called micromounts).

Properties

Mohs hardness
3.5
Luster
Vitreous
Streak
Light brown
Density
3.53
Cleavage
Perfect on {010}
Fracture
Uneven
Transparency
Transparent to Translucent
Crystal system
Triclinic

Diagnostic features

## Identification Identification of groatite is possible only through advanced analytical methods, such as Raman spectroscopy, X-ray diffraction (XRD), and chemical analysis (EDS/WDS). Visually, at the locality, it can be suspected based on its brown color, tabular crystal form, and co-occurrence with other rare phosphates. ## Distinguishing from Similar Minerals Groatite is very similar to other minerals from the alluaudite and wyllieite groups, with which it forms parageneses. Distinguishing it from them, e.g., from bobfergusonite, ferromerrillite, or johnsomervilleite, requires specialized laboratory analyses. All these minerals form similar, small, brown crystals. ## Crystal Forms Groatite crystallizes in the triclinic system. It forms very small, tabular or platy crystals, often flattened parallel to the cleavage plane. Crystals occur as single, dispersed individuals on the surface of other minerals.

Geological environment

## Genesis Groatite is a mineral of magmatic origin. It forms in the late stages of crystallization in complex granitic pegmatites, rich in phosphorus and lithium. It forms in vugs and small rock cavities. ## Mineral Associations This mineral co-occurs with other rare phosphates. At the type locality (Tanco Mine), it was found in association with bobfergusonite, eosphorite, lithiophilite, johnsomervilleite, wicksite, wodginite, and quartz. ## Localities The only confirmed locality for groatite in the world is the Tanco Mine, located on Bernic Lake in Manitoba, Canada. This is the type locality for this mineral.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of a groatite specimen is primarily assessed based on the presence of well-formed, sharp, and undamaged crystals, even if they are microscopic in size. A distinct, intense brown color is desirable. Specimens where groatite crystals are well-isolated and contrast with the rock matrix or other associated minerals are most highly valued. ## Popular Localities The only source of groatite specimens is the Tanco Mine in Canada. Material from this locality is extremely rare on the collector's market and appears sporadically, mainly circulating among specialists in rare minerals and micromounts.

Care and storage

## Cleaning Groatite specimens, due to their microscopic size and fragility, should generally not be cleaned mechanically or chemically. Any attempts at cleaning may lead to irreversible damage or loss of crystals. If it is necessary to remove loose dust, this can be done very carefully using a photographic air blower. ## What to Avoid Avoid contact with any chemicals, including acids and bases. Ultrasonic cleaners should not be used. The mineral is sensitive to shocks and mechanical damage. It should be protected from sudden temperature changes. ## Storage Groatite specimens (micromounts) should be stored exclusively in dedicated, sealed perky boxes, which protect them from dust, moisture, and mechanical damage. Display should only be done under a microscope.

Sources

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