Amblygonite

Chemical formula: LiAlPO<sub>4</sub>F

Amblygonite is a lithium and aluminum-rich phosphate, valued by collectors for its well-formed crystals with a vitreous luster and pastel colors.

## Characteristics Amblygonite is a mineral from the phosphate group, chemically composed of lithium, sodium, aluminum, and fluorine phosphate. It typically forms large, anhedral masses or poorly developed, prismatic crystals that can reach considerable sizes, sometimes even several meters. Well-formed, tabular or short-prismatic crystals are rarer. Its appearance is usually massive, and transparent gem-quality fragments are rare. ## Physical Properties This mineral is characterized by a hardness of 5.5-6 on the Mohs scale, making it relatively brittle. The luster is vitreous, transitioning to greasy or pearly on fracture surfaces. It is usually translucent, less often transparent or nearly opaque in massive aggregates. The density of amblygonite ranges from 2.98 to 3.11 g/cm³. ## Colors and Varieties Amblygonite most commonly occurs in shades of white, cream, pale yellow, greenish, bluish, or gray. Colorless, pink, or lilac specimens are rarer. The name montebrasite is used for the variety rich in hydroxyl (OH) instead of fluorine (F), although these terms are often used interchangeably for the entire amblygonite-montebrasite isomorphic series. ## History and Name The mineral's name, given in 1817 by August Breithaupt, comes from the Greek words *amblys* (blunt) and *gonia* (angle), referring to its poorly defined cleavage angles, close to 90°. It was discovered in Saxony (Germany). ## Uses Due to its high lithium content, amblygonite is locally used as a lithium ore. It also has significance in the ceramic industry for producing glazes. Transparent, attractively colored crystals are cut and used as gemstones, but their use is limited due to their brittleness and perfect cleavage. Primarily, however, it is a mineral valued by collectors.

Properties

Mohs hardness
5.5-6
Luster
Vitreous, pearly, greasy
Streak
White
Density
2.98-3.11
Cleavage
Perfect in one direction, good in two others
Fracture
Uneven to subconchoidal
Transparency
Transparent to translucent
Crystal system
Triclinic

Diagnostic features

## Identification Amblygonite is most easily recognized by its massive form, vitreous to greasy luster, and relatively high density for a light-colored mineral. Its perfect cleavage in one direction and good cleavage in several others are characteristic, often manifesting as flat, shiny fracture surfaces. Occurrence in lithium-rich granitic pegmatites is a key indicator. ## Distinguishing from Similar Minerals Amblygonite is sometimes confused with scapolite, orthoclase, plagioclase feldspars (especially albite), and spodumene. It differs from feldspars by its higher density and characteristic cleavage. Spodumene has different cleavage (at ~90°) and often exhibits a more fibrous structure. Scapolite has a lower specific gravity. Under laboratory conditions, a test for lithium (red flame) and phosphorus allows for unambiguous identification. ## Crystal Forms Amblygonite crystals are rare and usually short- or long-prismatic, often with a stout, rounded appearance. However, it most commonly forms compact, granular, or anhedral masses embedded in the host rock. Crystals can be partially or completely altered to other minerals, such as kaolinite or muscovite.

Geological environment

## Genesis Amblygonite is a typical mineral of lithium- and phosphorus-rich granitic pegmatites. It forms in the late stages of pegmatitic magma crystallization, under conditions of high concentration of volatile and rare elements. It can also occur in quartz veins cutting granites and in alluvium (river sediments) as a weathering-resistant mineral. ## Mineral Associations This mineral often co-occurs with other lithium minerals, such as spodumene, lepidolite, and elbaite (tourmaline), as well as with quartz, albite, orthoclase, muscovite, apatite, cassiterite, and tantalite. The presence of these associated minerals is a strong indication when searching for amblygonite. ## Localities The most important and well-known amblygonite localities are in Brazil (Minas Gerais and Goiás states), from which large gem-quality crystals originate. Other significant localities include the United States (California, South Dakota, Maine), Germany (Saxony), Sweden (Varuträsk), Namibia, Rwanda, Spain, and France.

Rarity

Not very common

For collectors

## Quality Criteria Well-formed, sharp, and undamaged amblygonite crystals are most prized by collectors. Transparent specimens with intense, attractive colors (e.g., yellow, green, blue) are highly valued, which is a rarity. Large, partially transparent masses with vibrant color are also sought after. Combinations with other pegmatite minerals, such as tourmalines or lepidolite, significantly increase the value and aesthetic appeal of the specimen. ## Market Prices The prices of amblygonite vary. Small, massive fragments or poorly formed crystals are relatively inexpensive. Prices increase with the quality of the crystals – their size, degree of transparency, and intensity of color. Well-formed, transparent crystals weighing several tens of grams can fetch prices from tens to several hundred dollars. Exceptional museum-quality specimens, especially from classic localities, can be significantly more expensive. ## Popular Localities Collectors particularly value specimens from Brazil, especially from the Linópolis and Governador Valadares regions in Minas Gerais, which are famous for large, yellow and greenish crystals. Classic specimens also come from the Keystone mine in South Dakota (USA) and from Saxony in Germany.

Care and storage

## Cleaning Amblygonite specimens should be cleaned very carefully. It is best to use a soft brush to remove dust. If necessary, the specimen can be rinsed in distilled water, then immediately and thoroughly dried with a soft cloth. Ultrasonic and steam cleaners should be avoided, as they can cause cracks along cleavage planes. ## What to Avoid Amblygonite is sensitive to sudden temperature changes and to acids. It should be protected from impacts and drops, as it is brittle and has perfect cleavage, meaning it easily breaks in specific directions. Prolonged exposure to strong sunlight is not recommended. ## Storage It is recommended to store amblygonite specimens in separate, padded boxes or on a soft surface to prevent scratches and mechanical damage. It should not be stored with harder minerals. When displaying, ensure it is in a stable location, away from shelf edges and high-traffic areas.

External references

Sources

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