Apatite-series

Chemical formula: Ca₅[PO₄]₃(F,Cl,OH)

A group of calcium phosphate minerals with varied chemical composition, forming well-developed, often hexagonal crystals in a wide range of colors.

## Characteristics Apatite is the name of a series of phosphate minerals, primarily comprising hydroxyapatite, fluorapatite, and chlorapatite, which can form solid solutions with each other. It rarely occurs in pure form, most often as fluorapatite or mixtures with one component dominating. It forms characteristic, well-developed, hexagonal crystals with a prismatic or tabular habit, terminated by pyramids or flat faces. It also occurs as granular, radial, botryoidal aggregates, and even massive, compact aggregates (phosphorite). ## Physical Properties Apatite's hardness is exactly 5 on the Mohs scale, making it a reference mineral. It is relatively brittle. The luster is most often vitreous, and on fracture surfaces, it can be greasy or resinous. It is usually translucent, less commonly fully transparent or opaque. The density ranges from 3.1-3.3 g/cm³ depending on the chemical composition. ## Colors and Varieties Apatite occurs in an exceptionally wide range of colors: most often it is green, blue, yellow, or colorless. Purple, pink, brown, and even black specimens are also found. Some varieties exhibit a cat's eye effect or pleochroism (a change in color depending on the viewing direction). Popular varieties include: - **Moroxite**: a blue-green, asparagus-colored variety. - **Asparagus stone**: yellow-green, resembling the color of asparagus. - **Trilliumite**: an intensely yellow variety from Canada. - **Manganese apatite**: a pink to purple variety with manganese admixture. ## History and Name The name "apatite" comes from the Greek word *apatáō* (ἀπατάω) meaning "to deceive" or "to mislead". It was given in 1786 by the German mineralogist Abraham Gottlob Werner, because the diversity of apatite's forms and colors often led to its confusion with other minerals, such as beryl, tourmaline, or olivine. ## Uses Apatite is the main source of phosphorus for industry. Massive, compact varieties called phosphorites are mined on a large scale for the production of phosphate fertilizers, phosphoric acid, and in the chemical industry. Transparent and attractively colored crystals are valued as collector's stones and gemstones, although its relatively low hardness limits its use in jewelry to items not exposed to frequent impacts.

Properties

Mohs hardness: 5
Luster: Vitreous to Sub-resinous
Streak: White
Density: 3.1-3.3
Cleavage: Indistinct on {0001} and {1010}
Fracture: Conchoidal to Uneven
Transparency: Transparent to Opaque
Crystal system: Hexagonal

Diagnostic features

## Identification The most important diagnostic feature of apatite is its reference hardness (5 on the Mohs scale) – it can be scratched by steel (e.g., a knife) but scratches glass itself. Its hexagonal (six-sided) crystal habit and vitreous luster are also characteristic. It reacts with acids, which distinguishes it from many similar minerals. ## Distinguishing from Similar Minerals - **Beryl (aquamarine, emerald)**: It is significantly harder (7.5-8), does not react with acids, and has a slightly lower density. - **Tourmaline**: Also significantly harder (7-7.5) and often exhibits strong pleochroism and characteristic striations on prism faces. - **Topaz**: Significantly harder (8), heavier, and has perfect cleavage in one direction. - **Fluorite**: Much softer (4), has perfect cleavage in four directions, and often exhibits intense fluorescence under UV light. ## Crystal Forms Apatite most often forms hexagonal crystals with a prismatic habit, ranging from short and thick (tabular) to long and acicular. Crystals are often terminated by flat pinacoids or simple hexagonal pyramids. It also occurs in radial, granular, botryoidal aggregates, and as massive rock aggregates (phosphorites).

Geological environment

## Genesis Apatite is an accessory mineral, widely distributed in almost all rock types. It forms under magmatic conditions, crystallizing from magma in intrusive igneous rocks (e.g., granites, syenites, gabbros) and extrusive rocks. It is a common component of pegmatites, where it forms the largest and best-developed crystals. It also occurs in metamorphic rocks, such as marbles and gneisses, and in hydrothermal veins. It also forms through sedimentary processes, creating phosphorite deposits of organic origin (accumulations of bones, excrement). ## Mineral Associations Depending on the environment of formation, apatite co-occurs with many minerals. In pegmatites, these include quartz, feldspars (orthoclase, albite), micas (muscovite, lepidolite), tourmaline, and beryl. In metamorphic rocks (marbles), it is accompanied by calcite, diopside, vesuvianite, and garnets. In hydrothermal veins, it can occur with fluorite, calcite, and sulfides. ## Localities Perfectly formed apatite crystals come from many places around the world. The most important include: - **Mexico**: Famous yellow, vitreous crystals from the Cerro de Mercado mine in Durango. - **Brazil**: Large, blue and green crystals from pegmatites in Minas Gerais. - **Russia**: Blue-green moroxites from the vicinity of Slavjanka on the Kola Peninsula. - **Canada**: Green and red crystals from Ontario and Quebec (e.g., Bancroft, Otter Lake). - **Madagascar**: Intensely blue, "neon" crystals, often heat-treated. - **Pakistan and Afghanistan**: Pink and purple crystals from pegmatites in mountainous regions. - **USA**: Purple crystals from Maine (Mount Apatite) and green ones from California. - **Morocco**: Massive phosphorite deposits in the Khouribga region.

Rarity

Common

For collectors

## Quality Criteria The most highly valued collector's specimens of apatite are characterized by a combination of several features. Intense and rare color (e.g., "neon" blue, deep purple, saturated pink) significantly increases value. Transparency (gem-quality specimens) and the absence of inclusions and fractures are also crucial. Ideally formed, sharp, undamaged crystals with a vitreous luster are much more desirable than massive forms. The attractiveness of a specimen increases when apatite occurs in an aesthetic composition with other minerals (e.g., on a matrix of quartz, feldspar, or calcite). ## Market Prices Apatite prices vary widely. Small, single crystals or fragments with weaker color can be purchased for a few to several tens of Polish zlotys. Medium-sized specimens (a few centimeters) with good color and form cost from 100 to 500 PLN. Large, well-formed crystals with intense color, especially on matrix, can reach prices from several hundred to several thousand PLN. The most expensive are rare, faceted gemstones of high clarity and weight, as well as exceptional museum-grade specimens. ## Popular Localities Collectors particularly value specimens from specific localities known for unique characteristics: - **Cerro de Mercado, Mexico**: for exemplary, vitreous, yellow crystals. - **Panasqueira, Portugal**: for green, tabular crystals grown on wolframite or quartz crystals. - **Sapo Mine, Brazil**: for characteristic, "grassy" green crystals on albite blades. - **Kola Peninsula, Russia**: for historical, blue-green moroxites. - **Bancroft, Canada**: for large, opaque, green-brown crystals in calcite.

Care and storage

## Cleaning Apatite specimens should be cleaned gently, using a soft brush (e.g., a child's toothbrush) and lukewarm water, preferably distilled. A small amount of neutral soap can be added. After washing, the specimen should be thoroughly rinsed and left to air dry completely at room temperature. ## What to Avoid Apatite is sensitive to acids – even weak acids (e.g., lemon juice, vinegar) can damage it, causing surface dullness. Ultrasonic and steam cleaners should be avoided, as they can cause fractures. The mineral is also sensitive to high temperatures and sudden temperature changes. Some varieties, especially blue and purple ones, may fade with prolonged exposure to intense sunlight. ## Storage Due to its hardness of 5 on the Mohs scale, apatite is susceptible to scratching by harder minerals such as quartz, beryl, or corundum. It should be stored separately, in a soft material, a zip-lock bag, or in a dedicated compartmentalized display box. Avoid storing in humid places.

Sources

IMA Mineral List (CNMNC)