Beraunite
Chemical formula: Fe<sup>3+</sup><sub>6</sub>(PO<sub>4</sub>)<sub>4</sub>O(OH)<sub>4</sub>·6H<sub>2</sub>O
Hydrated iron phosphate, forming characteristic, radial aggregates ranging in color from reddish-brown to greenish.
Description
## Characteristics Beraunite is a hydrated iron phosphate, valued by collectors for its unique forms. It most often occurs as spherical or hemispherical aggregates with a radial-fibrous structure, resembling small "suns" or sea urchins. Less frequently, it forms small, tabular crystals gathered in druses. Its appearance is very distinctive, and the aggregates can reach several centimeters in diameter. ## Physical Properties This mineral is relatively soft, with a Mohs hardness of 3-4, meaning it can be scratched by a copper wire. It has a vitreous luster, and is sometimes described as greasy on fresh surfaces. It is translucent, and its density is about 2.8 g/cm³. It exhibits good cleavage in one direction, and its fracture is uneven and splintery. ## Colors and Varieties Beraunite displays a wide range of colors, depending on the oxidation state of iron. The most common specimens are reddish-brown, orange-brown, and yellowish-brown. Fresh, unoxidized samples can be olive-green, dark green, or even blue-green. Over time, when exposed to air, they turn greener, then brown. There are no named commercial varieties. ## History and Name The mineral's name comes from its type locality - the Hrbek mine near the town of Beroun in the Czech Republic. It was first scientifically described in 1841 by the German mineralogist August Breithaupt. There are two polytypic varieties, differing slightly in crystal structure. ## Uses Beraunite has no industrial significance. However, it is a sought-after and valued collector's stone due to its attractive, radial forms and rich colors.
Diagnostic features
## Identification The most important diagnostic feature of beraunite is its characteristic, radial or spherical aggregates of fibrous crystals. The color, ranging from green to reddish-brown, combined with this form of occurrence, is usually sufficient for identification. The streak of fresh, unoxidized material has a characteristic olive-green color. ## Distinguishing from Similar Minerals Beraunite is sometimes confused with other secondary phosphates. - **Cacoxenite** usually forms acicular aggregates of golden-yellow or brownish color and has a more silky luster. - **Strengite** most often occurs as spherical aggregates or small crystals of purple, pink, or peach color. - **Rockbridgeite** is usually darker, from greenish-black to black, and denser than beraunite. ## Crystal Forms Well-formed, single crystals are rare and appear as small, flattened tablets. The dominant and most recognizable form are spherical, hemispherical, and fan-shaped aggregates with a radial internal structure, composed of tightly packed, fibrous crystals.
Geological environment
## Genesis Beraunite is a secondary mineral. It forms as a result of hydrothermal alteration or weathering of primary phosphate minerals (mainly triphylite and lithiophilite) in the oxidation zones of granitic pegmatites. It also occurs in some sedimentary iron deposits and in fissures and cracks of phosphorus-rich rocks. ## Mineral Associations This mineral often co-occurs with other secondary phosphates. In pegmatites, its typical associates are rockbridgeite, hureaulite, strengite, vivianite, stewartite, and triphylite. In iron ore deposits, it can occur in association with goethite and limonite. ## Localities Classic, historical specimens come from the type locality in the Czech Republic (Beroun). World-class beraunite has been found in pegmatites in Germany (Hagendorf, Pleystein in Bavaria). In the USA, beautiful specimens in the form of large, reddish-brown spheres come from pegmatites in the Black Hills region of South Dakota (e.g., Bull Moose mine) and from Coosa County, Alabama. It is also known from Portugal and Brazil.
Rarity
Uncommon
Collector aspects
## Quality Criteria The most desired specimens by collectors are those with well-formed, sharply defined, spherical or hemispherical aggregates, known as "suns". Intense, deep colors, especially reddish-brown and orange, are highly prized. The size of the aggregates is also very important – the larger the diameter, the more valuable the specimen. The attractiveness is enhanced by a contrasting rock matrix or an association with other rare phosphate minerals. ## Popular Localities The localities in Germany (Hagendorf-Süd) and the USA are considered classic and provide the best specimens. The Bull Moose mine in South Dakota is famous for large, reddish-brown beraunite spheres on matrix. Specimens from these localities command the highest prices and are the pride of many mineralogical collections.
Care and storage
## Cleaning Beraunite specimens should be cleaned very carefully. It is best to use a soft brush to remove dust. If necessary, the specimen can be rinsed in distilled water and then thoroughly dried. Ultrasonic cleaners or washing under pressurized running water should not be used, as this can damage the delicate, fibrous aggregates. ## What to Avoid The mineral is sensitive to chemicals, especially acids, which can damage it. As a hydrated mineral, it is also susceptible to changes under high temperatures – heating leads to water loss, causing an irreversible change in color and structure. Prolonged exposure to direct sunlight should be avoided, as it can accelerate oxidation processes and color change. ## Storage It is recommended to store beraunite specimens in closed, padded boxes or display cases to protect them from dust, mechanical damage, and sudden changes in humidity. Due to its low hardness, it should not be stored in contact with harder minerals.