Bobierrite

Chemical formula: Mg₃(PO₄)₂·₈H₂O

Bobierrite is a hydrated magnesium phosphate, forming colorless or whitish, acicular crystals with perfect cleavage.

## Characteristics Bobierrite is a hydrated magnesium phosphate, which in its pure form is colorless and transparent. It most often occurs as aggregates of fine, acicular or hair-like crystals, which can form radial aggregates or delicate, silky coatings. It is usually whitish or grayish-white due to light scattering on numerous tiny crystals. ## Physical Properties This mineral is very soft, with a Mohs hardness of only 2-2.5, meaning it can be scratched with a fingernail. It has perfect cleavage in one direction, causing crystals to easily separate into thin lamellae or fibers. The luster is vitreous on crystal surfaces, and on fibrous aggregates, it can be silky or pearly. It is a light mineral, with a density of about 2.2 g/cm³. ## Colors and Varieties Bobierrite is typically colorless, white, or grayish-white. No colored varieties or trade names are known. ## History and Name The mineral was first described in 1868. Its name honors P. A. Bobierre, a French agricultural chemist who first synthesized this substance. ## Uses Bobierrite has no industrial applications. It is a mineral primarily of interest to collectors specializing in rare minerals or phosphate mineral systematics.

Properties

Mohs hardness: 2-2.5
Luster: Vitreous
Streak: White
Density: 2.195
Cleavage: On {010}, perfect.
Fracture: Uneven
Transparency: Transparent
Crystal system: Monoclinic

Diagnostic features

## Identification Bobierrite can be identified by its characteristic acicular or hair-like crystals forming radial aggregates. Key features include very low hardness (2-2.5), perfect cleavage in one direction, pearly or silky luster on aggregates, and occurrence in specific environments, such as guano deposits or fossil bones. ## Distinguishing from Similar Minerals It can be confused with other white, fibrous secondary minerals, such as gypsum or brushite. It is distinguished from gypsum by its often aggregate form (radial aggregates) and environment of occurrence. From brushite, which is also a phosphate, it can be difficult to distinguish without advanced analysis, although brushite is slightly harder (2.5). ## Crystal Forms Crystals are typically elongated, acicular or hair-like, often flattened. They form radial or stellate aggregates, as well as delicate, silky or felt-like coatings on the surface of other materials.

Geological environment

## Genesis Bobierrite is a secondary mineral, forming in specific, phosphate- and magnesium-rich environments. It typically forms as a result of reactions between solutions derived from the decomposition of organic matter (e.g., bat or bird guano) and magnesium-containing rocks. It can also form from the alteration of fossil bones or teeth (e.g., mammoths) under appropriate geochemical conditions. ## Mineral Associations It often co-occurs with other phosphate minerals, such as newberyite, hannayite, struvite, brushite, as well as calcite and dolomite. ## Localities The type locality, where this mineral was first found, is the Mejillones Peninsula in Antofagasta Province, Chile, where it occurred in guano deposits. Other known localities include caves in Transylvania (Romania), the Tip Top Mine in South Dakota (USA), and sites associated with fossil remains in Siberia (Russia).

Rarity

Rare

For collectors

## Quality Criteria The most valued specimens by collectors are those with well-formed, large (for this mineral) crystals forming aesthetic, radial or stellate aggregates. Purity and lack of damage to the delicate crystals are important. Contrast with the rock matrix also enhances the specimen's attractiveness. ## Popular Localities Specimens from the classic locality in Chile are rare. Specimens from the Tip Top Mine in the USA, known for many rare phosphates, occasionally appear on the collector's market.

Care and storage

## Cleaning Bobierrite specimens are extremely delicate and sensitive to water. Mechanical cleaning is highly inadvisable. Dust can be removed very carefully using a soft brush or a photographic blower. ## What to Avoid Contact with water must be absolutely avoided, as it can dissolve or damage the delicate crystals. The mineral is very soft, so it must be protected from scratching and impacts. It should not be heated, as it will lose water and undergo transformation. Avoid contact with acids and other chemicals. ## Storage Bobierrite specimens should be stored in dry conditions, preferably in closed, padded display boxes or cabinets, to protect them from dust, moisture, and mechanical damage.

External references

https://www.mindat.org/min-701.html