Laurentthomasite

Chemical formula: Mg₂K(Be₂Al)Si₁₂O₃₀

A blue or greenish-yellow mineral from the osumilite group, discovered in Madagascar, distinguished by its unique chemical composition with beryllium and aluminum.

## Characteristics Laurentthomasite is a rare mineral belonging to the osumilite group. It forms hexagonal, tabular or prismatic crystals, often small, not exceeding a few millimeters. Its most characteristic feature is an intense, cobalt-blue color, although specimens with greenish-yellow hues are also found. It is a transparent mineral, which, combined with its vivid color, gives it an attractive appearance. ## Physical Properties This mineral is characterized by a hardness of 6 on the Mohs scale, placing it on par with orthoclase. It has a density of 2.67 g/cm³, typical for many silicates. Laurentthomasite's luster is vitreous. It exhibits weak cleavage in one direction ({0001}), and its fracture is uneven to conchoidal. ## Colors and Varieties The dominant and most desired color is a deep, cobalt blue. Greenish-yellow crystals also occur. No distinct commercial or gemological varieties of this mineral have been identified due to its rarity and small crystal sizes. ## History and Name Laurentthomasite was officially recognized as a new mineral species by the International Mineralogical Association (IMA) in 2019. Its name honors Laurent Thomas (born 1971), a French mineralogist and gemologist, who made significant contributions to the study of Madagascar's mineralogy and was the first to find this mineral. ## Uses Due to its extreme rarity, small crystal sizes, and limited occurrence, laurentthomasite has no industrial applications. It is solely an object of scientific interest and a valuable acquisition for specialized mineral collectors.

Properties

Mohs hardness: 6
Luster: Vitreous
Streak: Blue
Density: 2.67
Cleavage: poor {0001} cleavage
Fracture: Irregular/Uneven,Conchoidal
Transparency: Transparent
Crystal system: Hexagonal

Diagnostic features

## Identification The key diagnostic features of laurentthomasite are its intense, cobalt-blue color, hexagonal crystal habit, and specific occurrence environment. A blue streak is also characteristic. However, final confirmation of its identity requires advanced analytical methods, such as Raman spectroscopy or chemical composition analysis (EDS), due to its similarity to other minerals in the osumilite group. ## Distinguishing from Similar Minerals Laurentthomasite can be confused with other blue minerals from its group, such as osumilite-(Mg) or sugilite, as well as lazurite or hauyne. It is distinguished from them by its specific chemical composition (presence of beryllium and potassium), hardness (6 on the Mohs scale), and characteristic association with other minerals at its discovery site. Unlike lazurite, it does not react with hydrochloric acid. ## Crystal Forms This mineral forms well-developed, hexagonal crystals with a tabular or short-prismatic habit. Crystals are typically small, reaching up to several millimeters in length and width. They occur as single crystals embedded in the host rock.

Geological environment

## Genesis Laurentthomasite forms under specific geological conditions, in skarns or pegmatites enriched in beryllium. Its formation is associated with metamorphic and metasomatic processes at the contact of magmatic intrusions with carbonate rocks, in the presence of elements such as beryllium, potassium, and magnesium. ## Mineral Associations This mineral occurs in association with other rare minerals. At its type locality (Beravina, Madagascar), it was found in association with diopside, scapolite, spinel, phlogopite, poudretteite, lisitsynite, and other beryllium silicates. ## Localities The only confirmed and described locality for laurentthomasite in the world is its type locality: a quarry in the Beravina area, Betroka district, Anosy region, Madagascar.

Rarity

Extremely rare

For collectors

## Quality Criteria The most highly prized laurentthomasite specimens are those with well-formed, sharp crystals of intense, cobalt-blue color and high transparency. The contrast with a light host rock (matrix) on which the crystal is embedded is also of great importance. Specimens with visible damage or a less distinct, greenish color are valued lower. Due to their small size, even millimeter-sized crystals with good parameters are considered valuable. ## Popular Localities The only source of laurentthomasite specimens is its type locality in Madagascar. All minerals available on the collector's market originate from this single location, making them highly sought after by collectors specializing in rare minerals or minerals from the osumilite group.

Care and storage

## Cleaning It is recommended to clean specimens only with a soft brush to remove dust. The use of water, especially with detergents, is not advisable without absolute necessity. If washing is essential, use distilled water and immediately dry the specimen thoroughly. ## What to Avoid Avoid contact with chemicals, acids, and strong cleaning agents, which can damage the mineral's surface. Do not subject it to ultrasonic or steam cleaning. Due to its hardness of 6, it is susceptible to scratches from harder minerals (e.g., quartz), so avoid contact with them. ## Storage Laurentthomasite specimens, especially those on rock matrix, should be stored in separate, padded collector boxes to protect them from mechanical damage and scratching. They should be protected from dust and sudden temperature changes.

External references

https://www.mindat.org/min-53556.html