Anthophyllite

Chemical formula: &#9744;Mg<sub>2</sub>Mg<sub>5</sub>Si<sub>8</sub>O<sub>22</sub>(OH)<sub>2</sub>

Anthophyllite is a mineral from the amphibole group, forming characteristic fibrous or lamellar aggregates with colors ranging from gray to greenish-brown.

## Characteristics Anthophyllite is a mineral from the amphibole group, belonging to an isomorphic series with cummingtonite. It forms fibrous, asbestiform, lamellar, or radial aggregates. Well-formed, prismatic crystals are rare. Its name refers to its clove-brown color, resembling the color of a carnation flower (from Greek *anthophyllum* - carnation). ## Physical Properties This mineral is characterized by a hardness of 5.5-6 on the Mohs scale and a density in the range of 2.9-3.2 g/cm³. It possesses excellent cleavage in two directions, intersecting at an angle of approximately 120 degrees, which is typical for amphiboles. The luster is vitreous on crystal surfaces and can be silky on fibrous aggregates. ## Colors and Varieties Anthophyllite most commonly exhibits colors ranging from grayish, through yellowish-brown, clove-brown, to greenish-brown. Its color is related to its iron content. The magnesium-rich variety is usually colorless or light gray. Darker shades indicate a higher iron content. One variety is amosite – a trade name for anthophyllite asbestos, mainly from South Africa. ## History and Name The name anthophyllite, given in 1801 by Christian Friedrich Schumacher, comes from the Latin word *anthophyllum*, meaning carnation, in reference to its typical color. This mineral was known and described from localities in Norway (Kongsberg) and Greenland. ## Uses Fibrous varieties of anthophyllite, known as anthophyllite asbestos, had limited use as thermal insulation and fire-resistant material. Currently, due to the harmfulness of asbestos dust to health, its use has been discontinued. For collectors, anthophyllite is mainly interesting as a rock-forming mineral and for its characteristic aggregate forms.

Properties

Mohs hardness
5.5-6
Luster
Vitreous, Pearly
Streak
White, Gray
Density
2.9-3.2
Cleavage
Perfect on {210}
Fracture
Uneven
Transparency
Translucent to Opaque
Crystal system
Orthorhombic

Diagnostic features

## Identification Anthophyllite is identified by its fibrous or lamellar habit, characteristic amphibole cleavage (two directions at ~120°), and color, most often in shades of brown and green. Vitreous to silky luster is also a helpful feature. ## Distinguishing from Similar Minerals Anthophyllite is sometimes confused with other amphiboles, such as cummingtonite or tremolite. Distinguishing it from cummingtonite, with which it forms a series, without advanced analyses (e.g., X-ray diffraction) is often impossible. It usually differs from tremolite by its darker, brownish color (tremolite is typically white or light green). It is distinguished from asbestiform serpentines (chrysotile) by its greater hardness and brittleness of fibers. ## Crystal Forms Anthophyllite crystals are rare, prismatic, and columnar. It usually forms fibrous, lamellar, radial, or granular aggregates. The fibers can be flexible but are not elastic.

Geological environment

## Genesis Anthophyllite is a product of regional and contact metamorphism of ultramafic rocks (e.g., peridotites, dunites) and magnesium-contaminated sedimentary rocks, such as dolomites or marls. It forms under conditions of medium to high temperatures and pressures. It is a typical component of some amphibolites, serpentinites, and talc schists. ## Mineral Associations This mineral often coexists with talc, cordierite, phlogopite, olivine, cummingtonite, tremolite, sillimanite, kyanite, and garnets (mainly pyrope). ## Localities Significant deposits and occurrences of anthophyllite are known from many places worldwide. The most important include: Kongsberg and Snarum in Norway; the Telemark region (Norway) and Dalarna (Sweden); numerous localities in Finland (e.g., Paakkila); Greenland (Nuuk area); the states of Georgia, North Carolina, Montana, and Massachusetts in the USA. It also occurs in South Africa, from where the commercial asbestos variety – amosite – originated.

Rarity

Not very common

For collectors

## Quality Criteria The most prized by collectors are specimens with well-formed, large crystals, which are rare. Aggregates with a radial habit ("anthophyllite suns") or specimens with an intense, clove-brown color are also attractive. Association with other minerals, such as red garnets, creating an aesthetic contrast, is also important. ## Popular Localities Classic, valued specimens come from historical localities in Norway (Kongsberg, Snarum) and from Hermannov in the Czech Republic. Specimens from the USA, particularly from North Carolina (Balsam Gap), are also sought after. Large, radial aggregates have been found in New Hampshire.

Care and storage

## Cleaning Anthophyllite specimens should be cleaned very carefully, preferably dry, using a soft brush or compressed air. For heavier dirt, a damp cloth can be used, but avoid soaking the specimen, especially if it is fibrous. Ultrasonic cleaners should be avoided, as they can damage delicate aggregates. ## What to Avoid It is absolutely essential to avoid inhaling dust from fibrous (asbestiform) specimens, as it is carcinogenic. The mineral is sensitive to strong acids. It should not be heated or exposed to rapid temperature changes. ## Storage Fibrous specimens should be stored in closed, airtight containers or display cases to prevent the spread of fibers. Crystalline or massive specimens are less problematic, but it is still advisable to protect them from dust and mechanical damage.

External references

Sources

Read more