Pinnoite

Chemical formula: MgB<sub>2</sub>O(OH)<sub>6</sub>

Pinnoite is a colorless or pale yellow magnesium borate, forming radial aggregates of acicular crystals.

## Characteristics Pinnoite is a mineral from the borate group, chemically hydrated magnesium borate. It most often occurs in fibrous, radial, or spherulitic aggregates, composed of small, acicular crystals. Less frequently, it forms single, well-formed crystals with a columnar or acicular habit, exhibiting vertical striations. It is a brittle mineral. ## Physical Properties Pinnoite is characterized by a hardness of 3.5 on the Mohs scale. Its crystals have a vitreous luster, while fibrous aggregates have a silky luster. It is transparent to translucent. The mineral's density is approximately 2.2 g/cm³. ## Colors and Varieties This mineral is usually colorless, white, grayish, or pale yellow to greenish-yellow. No color or commercial varieties are distinguished. ## History and Name The name pinnoite comes from the surname of Johann Friedrich Hermann Pinno (1773-1844), a mining counselor (Bergrat) from Halle, Germany, who first analyzed this mineral. The mineral was first described in 1884 by Karl Alphons M. Stremme. ## Uses Pinnoite is a mineral of interest mainly to collectors and scientists. It has no significant industrial application, although, along with other borates, it can be a minor source of boron in deposits where it occurs in larger quantities.

Properties

Mohs hardness
3.5
Luster
Vitreous, Silky
Streak
White
Density
2.2
Cleavage
Good on {110}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Tetragonal

Diagnostic features

## Identification Pinnoite is most easily recognized by its characteristic forms of occurrence – radial or spherulitic aggregates composed of small, acicular crystals. The silky luster in fibrous aggregates is also a helpful feature. It reacts with acids and is partially soluble in water. ## Distinguishing from Similar Minerals Pinnoite is sometimes confused with other borates that form fibrous aggregates, such as colemanite or ulexite. Ulexite is distinguished by the characteristic "television stone" effect (image transmission), which pinnoite does not exhibit. Colemanite is harder (4.5 on the Mohs scale). Final differentiation often requires chemical or crystallographic analysis. ## Crystal Forms Pinnoite crystals are tetragonal, with a columnar or acicular habit, often with visible vertical striations on the faces. They usually form fibrous, radial, spherulitic, or massive, granular aggregates.

Geological environment

## Genesis Pinnoite is an evaporite mineral. It forms by precipitation from boron-rich solutions in drying saline lakes and lagoons, in arid and hot climates. It forms in potash-magnesium salt deposits. ## Mineral Associations This mineral often co-occurs with other borates and salts, such as boracite, kainite, halite, sylvite, carnallite, and anhydrite. ## Localities The most important and classic occurrences of pinnoite are found in Germany, in potash salt deposits near Stassfurt (Saxony-Anhalt) and Hanover. It is also known from Wieliczka in Poland, from Kazakhstan (Inder salt deposit), and from several localities in the USA (California, New Mexico) and China.

Rarity

Not very common

For collectors

## Quality Criteria The most valued by collectors are specimens with well-formed, transparent crystals, which are rare. Aesthetic, spherical aggregates (spherulites) with a silky luster are also highly prized, especially if they are embedded in a contrasting rock matrix. The size and completeness of radial aggregates also affect their value. ## Popular Localities Classic, historical specimens come from German salt mines in the Stassfurt region. Currently, specimens from Kazakhstan and China, which may be characterized by good crystal development, also appear on the collector's market.

Care and storage

## Cleaning Pinnoite specimens should be cleaned very carefully, using a soft brush to remove dust. Due to its partial solubility in water, contact with water should be avoided. If a liquid is necessary, alcohol can be used, but with great caution and for a very short time, then the specimen should be thoroughly dried. ## What to Avoid Contact with water, especially hot water and acids, in which pinnoite dissolves, should be absolutely avoided. The mineral is brittle and sensitive to impacts and temperature changes. It should not be exposed to direct sunlight. ## Storage It is recommended to store pinnoite in a dry place, preferably in a closed container or display cabinet away from sources of moisture. To prevent mechanical damage, it should be kept away from harder minerals.

External references

Sources

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