Loomisite

Chemical formula: Ba[Be₂P₂O₈]·H₂O

Loomisite is a very rare, hydrated barium beryllophosphate from the zeolite group, forming colorless or white, transparent crystals.

## Characteristics Loomisite is a very rare mineral from the zeolite group, chemically classified as a hydrated barium beryllophosphate. It occurs as small, tabular or bladed crystals, rarely exceeding 1 mm in length. It typically forms aggregates or rosette-like clusters. It is a transparent mineral, colorless to white, with a vitreous luster. ## Physical Properties This mineral is characterized by a hardness of 3.5-4 on the Mohs scale, making it relatively soft. Its density is approximately 3.46 g/cm³. It exhibits distinct cleavage in two directions. ## Colors and Varieties Loomisite is a colorless to white mineral. No colored varieties or trade names have been distinguished. ## History and Name Loomisite was first described in 1988 by Pete J. Dunn and colleagues. The mineral is named in honor of Thomas H. Loomis (born 1943), an American mineral collector from South Dakota, who specialized in pegmatite minerals and discovered this mineral. ## Uses Due to its extreme rarity and small crystal size, loomisite has no industrial applications. It is solely an object of scientific and collecting interest for specialized micromineral collectors.

Properties

Mohs hardness
3.5-4
Luster
Vitreous
Streak
White
Density
3.46
Cleavage
{100} and <mi>{_110}</mi>.
Fracture
Uneven
Transparency
Transparent
Crystal system
Monoclinic

Diagnostic features

## Identification Identifying loomisite in the field is practically impossible without specialized equipment. In a collection, it is identified based on its characteristic appearance – small, white, tabular crystals with a vitreous luster, assembled into rosette aggregates. Its association with the locality (granitic pegmatites) and accompanying minerals is key. ## Distinguishing from Similar Minerals Loomisite can be confused with other rare pegmatite phosphates, such as Childrenite or Eosphorite, which can form similar aggregates. Differentiation requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical composition analysis (EDS), due to its specific chemical composition containing barium and beryllium. ## Crystal Forms Loomisite crystallizes as thin, tabular or bladed crystals, often flattened. These crystals typically combine into fan-like or rosette aggregates.

Geological environment

## Genesis Loomisite is a hydrothermal mineral, forming in the late stages of crystallization of complex granitic pegmatites. It forms in rock cavities and fissures as a result of the action of solutions rich in barium, beryllium, and phosphorus. ## Mineral Associations This mineral co-occurs with other phosphate minerals typical of pegmatites. At its type locality (Big Chief Mine), it was found in association with montgomeryite, childrenite, eosphorite, roscherite, and wardite. ## Localities The only confirmed and described occurrence of loomisite in the world is its type locality: the Big Chief Mine in Pennington County, South Dakota, USA.

Rarity

Very rare

For collectors

## Quality Criteria The quality of a loomisite specimen is primarily assessed based on the size and development of crystal aggregates. The most valued specimens are those with clearly formed, sharp rosettes or fans of crystals, contrastingly set on a rock matrix. The clarity and transparency of individual crystals also increase the value of the specimen, although due to their small size, this is a secondary characteristic. ## Popular Localities The only source of loomisite specimens is the Big Chief Mine in South Dakota, USA. All specimens available on the collector's market come from this single locality.

Care and storage

## Cleaning Loomisite specimens, due to their small size and delicacy, should be cleaned with utmost care. It is recommended to use compressed air to remove dust. If wet cleaning is necessary, use only distilled water and a very soft brush, avoiding strong pressure. ## What to Avoid Avoid contact with acids and other chemicals that can damage the mineral. Loomisite is relatively soft, so it must be protected from scratching by harder minerals. It should not be heated or cleaned with ultrasonics. ## Storage Loomisite specimens, as microminerals, are best stored in specialized "micromount" boxes that protect them from dust, mechanical damage, and direct contact. Avoid exposure to moisture and extreme temperatures.

External references

Sources

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