Nordstrandite

Chemical formula: Al(OH)<sub>3</sub>

Nordstrandite is a rare polymorph of aluminum hydroxide, most commonly forming small, colorless or white platy crystals.

## Characteristics Nordstrandite is one of four polymorphs of aluminum hydroxide [Al(OH)₃]. It occurs as small, well-formed crystals with a platy or lamellar habit. These crystals often form fan-shaped, radial, or spherulitic aggregates. Due to the small size of the crystals, its macroscopic features are difficult to observe without magnification. ## Physical Properties This mineral is relatively soft, with a hardness of about 3 on the Mohs scale. It has a vitreous luster, and a pearly luster on cleavage planes. It is transparent to translucent. Its density is approximately 2.43 g/cm³. ## Colors and Varieties Nordstrandite is typically colorless or white. It can sometimes be colored gray or yellowish by impurities and inclusions. No named color varieties or commercial varieties are distinguished. ## History and Name The mineral's name, given in 1964, honors Robert A. van Nordstrand, a chemist at Sinclair Research who first synthesized the substance in 1956. Nordstrandite was identified as a mineral in samples from Sarawak, Malaysia, and from Guam. ## Uses Nordstrandite has no significant industrial application. It is primarily an object of scientific interest, as one of the polymorphs of aluminum hydroxide, and of collector interest due to its rarity and forms of occurrence.

Properties

Mohs hardness
3
Luster
Vitreous to Pearly
Streak
White
Density
2.43
Cleavage
Perfect on {001}
Fracture
Uneven
Transparency
Transparent to Translucent
Crystal system
Triclinic

Diagnostic features

## Identification Identifying nordstrandite based on visual characteristics is very difficult. It is characterized by low hardness, pearly luster on cleavage planes, and occurrence as small, platy crystals forming radial aggregates. It reacts with acids and bases. Definitive identification requires advanced analytical methods, such as X-ray diffraction (XRD). ## Distinguishing from Similar Minerals Nordstrandite is visually indistinguishable from its polymorphs: gibbsite, bayerite, and doyleite. All form similar, white or colorless crystals and have similar physical properties. It can also be confused with other soft, white minerals, such as kaolinite or brucite, but crystal habit and environment of occurrence can be helpful in preliminary identification. ## Crystal Forms Nordstrandite crystals are platy or lamellar, with a hexagonal or tetragonal outline. They most often occur as radial, fan-shaped, or spherical aggregates. Single, isolated crystals are rarely found.

Geological environment

## Genesis Nordstrandite is a low-temperature mineral, forming under low-pressure conditions. It forms as a result of weathering of aluminum-rich rocks, especially in bauxites and laterites. It can also crystallize in fissures and voids of carbonate rocks, in lake sediments, and in low-temperature hydrothermal veins. ## Mineral Associations It most often co-occurs with its polymorphs - gibbsite, bayerite, and doyleite. It is also accompanied by other minerals of the weathering zone, such as kaolinite, halloysite, diaspore, boehmite, as well as calcite and dolomite in carbonate environments. ## Localities Important nordstrandite localities include Sarawak on Borneo Island (Malaysia), where it was first identified in nature, and Guam. It is also found in Sag-bulo, Hungary, in various localities in Russia (e.g., the Urals), Italy, and Australia.

Rarity

Rare

For collectors

## Quality Criteria For collectors, the most valuable specimens are those with well-formed, sharp crystals forming aesthetic, radial or fan-shaped aggregates. The size of the crystals is of great importance – specimens with crystals visible to the naked eye, and not just under a microscope, are much more highly valued. Specimens on a contrasting rock matrix that highlights the delicate, white nordstrandite aggregates are also desirable. ## Popular Localities Specimens of collector's significance mainly come from classic localities, such as Sarawak (Malaysia) and from some localities in Russia and Italy, where well-formed crystalline aggregates have been found.

Care and storage

## Cleaning Nordstrandite specimens should be cleaned very carefully due to their softness and perfect cleavage. It is recommended to use a soft brush to remove dust. If necessary, the specimen can be rinsed in distilled water, then gently dried with compressed air or allowed to air dry. Ultrasonic cleaners should be avoided. ## What to Avoid Nordstrandite is sensitive to acids and strong bases, in which it dissolves. It should be protected from contact with chemicals. As a soft mineral, it is susceptible to scratching by harder minerals (quartz, feldspars). It should not be exposed to high temperatures. ## Storage Nordstrandite specimens are best stored in separate, padded boxes or on stands, away from harder minerals, to avoid scratches and mechanical damage. Due to the small size of the crystals, it is advisable to protect them from dust in closed display cases or containers.

External references

Sources

Read more