Brandholzite

Chemical formula: MgSb<sup>5+</sup><sub>2</sub>(OH)<sub>12</sub>·6H<sub>2</sub>O

Brandholzite is a very rare, hydrated magnesium antimonate, forming colorless, tabular crystals with a hexagonal outline.

## Characteristics Brandholzite is a hydrated magnesium antimonate belonging to the brandholzite group. This mineral forms very small, colorless, tabular crystals, which typically do not exceed 0.2 mm in diameter. The crystals tend to form hexagonal outlines and often occur as radial or randomly oriented clusters and aggregates. Due to the small size of the crystals, its macroscopic features are difficult to observe without magnification. ## Physical Properties Brandholzite is characterized by a hardness of approximately 2 on the Mohs scale, making it a very soft mineral. It has a pearly luster on cleavage surfaces and a vitreous luster on other faces. It is transparent. The density calculated based on the formula and unit cell parameters is 3.11 g/cm³. ## History and Name The mineral was discovered in Brandholz, in the Fichtelgebirge mountain range in Bavaria (Germany). Its name comes directly from the type locality (the place of its first finding). It was approved as a new mineral species by the International Mineralogical Association (IMA) in 1998 (IMA1998-008). It was described by a team of mineralogists: J. Schlüter, K-H. Klaska, G. Adiwidjaja, G. Gebhard.

Properties

Mohs hardness
2
Luster
Pearly, Vitreous
Streak
White
Density
3.11
Cleavage
Perfect on {0001}
Fracture
Uneven
Transparency
Transparent
Crystal system
Trigonal

Diagnostic features

## Identification Identification of brandholzite in practice relies on chemical (EDS) and structural (XRD) analysis, due to its extreme rarity and microscopic crystal size. Visually, at the occurrence site, it can be suspected based on its association with other antimony minerals, especially in the oxidation zones of deposits. ## Distinguishing from similar minerals Brandholzite is structurally related to bottinoite, which contains nickel instead of magnesium. Distinguishing these two minerals requires advanced analytical methods. It can be confused with other secondary, colorless or white antimony minerals, but its characteristic morphology and chemical composition are key for identification. ## Crystal forms Brandholzite crystallizes as thin, tabular crystals with a hexagonal outline. These crystals form rosette-like, radial, or chaotic aggregates on the surface of the host rock.

Geological environment

## Genesis Brandholzite is a secondary mineral, forming in the oxidation zones of hydrothermal ore deposits rich in antimony. It forms as a result of the weathering of primary antimony minerals, such as stibnite, in the presence of magnesium-rich solutions. ## Mineral associations This mineral co-occurs with other secondary minerals of the oxidation zone. In the type locality (Brandholz, Germany), it was found in association with stibnite, kermesite, senarmontite, valentinite, bottinoite, and quartzite. ## Localities Brandholzite is an extremely rare mineral. Apart from the type locality in Brandholz, Bavaria (Germany), its occurrence has only been confirmed in the Cetine di Cotorniano mine in Tuscany (Italy).

Rarity

Extremely rare

For collectors

## Quality criteria As a microscopic mineral, brandholzite is valued primarily for its mere presence in a specialized collection. The most highly rated specimens are those that show well-formed, though still microscopic, crystals with a distinct hexagonal outline, forming aesthetic aggregates. A rich association with other rare secondary minerals is also important. ## Popular localities Both known localities, Brandholz in Germany and Cetine di Cotorniano in Italy, provide specimens of scientific and collector's significance. Due to its extreme rarity, specimens from either of these locations are highly prized by specialized collectors of systematic minerals and micromounts.

Care and storage

## Cleaning Brandholzite specimens are extremely delicate and small, so mechanical cleaning should be avoided. If absolutely necessary, compressed air (from a safe distance) can be used to remove loose dust particles. Contact with water should be avoided, as it can affect the hydrated structure of the mineral. ## What to avoid Contact with chemicals, acids, and detergents must be strictly avoided. The mineral is very soft and susceptible to scratching. It should be protected from high temperatures, which can cause dehydration (loss of water) and destruction of the crystal structure. Avoid ultrasonics. ## Storage Brandholzite specimens should be stored under stable conditions, in sealed "micromount" containers, to protect them from mechanical damage, dust, and humidity changes. Due to their small size, these are exclusively microscopic specimens.

Sources

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