Graftonite-(Ca)

Chemical formula: CaFe₂+₂(PO₄)₂

Graftonite-(Ca) is a rare phosphate mineral, occurring in granitic pegmatites, typically as granular or massive aggregates of salmon-pink color.

## Characteristics Graftonite-(Ca) is a phosphate mineral belonging to the graftonite group. It is the calcium analogue of graftonite-(Fe) and graftonite-(Mn). It most commonly forms anhedral (irregularly shaped) grains and massive aggregates; thick, tabular crystals are rare. Its appearance is usually inconspicuous, and specimens are intergrown with the host rock. The mineral is characterized by a vitreous or slightly resinous luster. ## Physical Properties The Mohs hardness of graftonite-(Ca) is 5, placing it on par with apatite. It is a relatively brittle mineral. Its density ranges from 3.73 to 3.77 g/cm³, which is quite high for a phosphate. It is translucent, and in thicker sections, opaque. ## Colors and Varieties This mineral exhibits characteristic colors ranging from salmon-pink and reddish-brown to reddish-brown and brown. It does not form color varieties or commercial forms. Its name, according to mineralogical nomenclature, indicates the dominance of calcium (Ca) in a specific position within its crystal structure. ## History and Name The name of the mineral group – graftonite – originates from the primary discovery locality in Grafton, New Hampshire, USA. Graftonite-(Ca) as a distinct mineral was formally approved by the International Mineralogical Association (IMA) relatively recently, after detailed chemical analysis of samples from various locations. The suffix "-(Ca)" distinguishes it from other members of the group with dominant iron or manganese. ## Uses Graftonite-(Ca) has no industrial applications. It is solely an object of scientific and collecting interest, valued by specialists collecting rare pegmatite minerals.

Properties

Mohs hardness: 5
Luster: Vitreous to Resinous
Streak: White
Density: 3.73-3.77
Cleavage: Good on {010}
Fracture: Uneven to Sub-Conchoidal
Transparency: Translucent to Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Helpful identification features include: characteristic salmon-pink or brownish color, vitreous to resinous luster, and occurrence as granular masses within granitic pegmatites. The presence of associated, often rare, phosphates is crucial. ## Distinguishing from Similar Minerals The biggest challenge is distinguishing graftonite-(Ca) from other minerals in the graftonite group (graftonite-(Fe) and graftonite-(Mn)), which is impossible without advanced chemical analysis (e.g., EDS). It can be confused with massive aggregates of triplite or sarcopside, with which it often co-occurs, but it differs from them in physical properties, such as cleavage. From similarly colored garnets (e.g., spessartine), it is distinguished by lower hardness and a different type of fracture. ## Crystal Forms Well-formed crystals are extremely rare. It usually occurs as anhedral grains, compact aggregates, and massive forms. It often forms lamellar intergrowths and exsolution textures with other phosphates, resulting from solid-state exsolution processes.

Geological environment

## Genesis Graftonite-(Ca) is a primary phosphate mineral, crystallizing in the late stages of evolution of complex granitic pegmatites, rich in lithium and phosphorus. It often forms as a result of exsolution from primary, homogeneous crystals of the graftonite-beusite series. ## Mineral Associations This mineral occurs in association with other, often rare, pegmatite phosphates. Its most common associations include: triphylite, lithiophilite, sarcopside, wolfeite, zwieselite, vivianite, ludlamite, and minerals from the arrojadite group. ## Localities The type locality for graftonite-(Ca) is the Bull Moose Mine in Custer County, South Dakota (USA). It is also known from the historical locality of the graftonite group – the Palermo No. 1 Mine in Grafton, New Hampshire (USA). Other confirmed occurrences include pegmatites in San Luis Province, Argentina, and the Kimitoön region in Finland.

Rarity

Rare

For collectors

## Quality Criteria The most highly valued specimens are those with an intense, salmon color and forming the largest possible, homogeneous aggregates. A significant added value is the association with well-formed crystals of other rare phosphates. Since graftonite-(Ca) crystals are almost never found, even fragments showing partial development of crystal faces are considered exceptional. ## Popular Localities Specimens from American localities: Bull Moose Mine in South Dakota and Palermo No. 1 Mine in New Hampshire, are considered classic and most sought after by collectors. Material from these localities was used to describe the mineral and its group.

Care and storage

## Cleaning Graftonite-(Ca) specimens should be cleaned very carefully, using a soft brush and distilled water. Ultrasonic cleaners should be avoided, as they could damage the brittle mineral or cause it to fracture along cleavage planes. ## What to Avoid The mineral is sensitive to strong acids. It should be protected from scratching by harder minerals (e.g., quartz). It is stable under normal conditions and does not show sensitivity to sunlight or humidity changes. ## Storage It is recommended to store specimens in separate, padded boxes or display cases to avoid contact with other, harder minerals. Display in a closed cabinet is safe and does not require special conditions.

Sources

IMA Mineral List (CNMNC)