Englishite

Chemical formula: K₃Na₂Ca₁₀Al₁₅(OH)₇(PO₄)₂₁·₂₆H₂O

Englishite is a rare, hydrated phosphate of potassium, sodium, calcium, and aluminum, forming small, white aggregates and platy crystals.

## Characteristics Englishite is a complex, hydrated phosphate mineral belonging to the englishite group. It most commonly occurs as aggregates of small, bladed or platy crystals, which rarely exceed 1 mm in length. It also forms radial or spherulitic aggregates, and sometimes coatings and crusts. Individual crystals are usually colorless to white, and their aggregates are white. ## Physical Properties Englishite crystals exhibit a hardness of approximately 3 on the Mohs scale. They are brittle and have a pearly luster, especially noticeable on cleavage planes, or vitreous luster. The mineral is transparent to translucent. Its density is approximately 2.66 g/cm³. ## Colors and Varieties This mineral is usually colorless or white. No colored or commercial varieties are distinguished. ## History and Name Englishite was first described in 1930 by Duncan McConnell and John W. Gruner. The mineral is named in honor of George

Properties

Mohs hardness: 3
Luster: Pearly
Streak: White
Density: 2.66
Cleavage: Perfect on {010}
Fracture: Uneven
Transparency: Transparent to translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Englishite can be identified by its occurrence as small, white, platy or bladed crystals, often forming radial aggregates. Its characteristic pearly luster on cleavage planes and its association with other rare phosphate minerals in a specific geological environment are also distinctive. ## Distinguishing from Similar Minerals It can be confused with other white secondary minerals such as wardite, crandallite, or montgomeryite, with which it often co-occurs. Definitive differentiation requires advanced analytical methods, such as X-ray diffraction (XRD), due to visual similarity and small crystal sizes. ## Crystal Forms Crystals are most often platy or bladed, elongated along one axis. They typically form fan-shaped, radial, or spherulitic aggregates, as well as crusts on other minerals.

Geological environment

## Genesis Englishite is a secondary mineral, formed in the oxidation zones of phosphate deposits. It forms as a result of low-temperature hydrothermal processes or weathering acting on rocks rich in phosphorus and aluminum, such as phosphorites or phosphate pegmatites. ## Mineral Associations This mineral often co-occurs with other phosphates, such as montgomeryite, overite, wardite, crandallite, millisite, as well as with quartz, wavellite, and apatite. ## Localities The most important and classic locality, from which the best specimens originate, is the "Clay Canyon" mine near Fairfield in Utah County, USA. This is the type locality for this mineral. It is also known from several other locations in Utah, as well as from Australia (Iron Monarch mine, Iron Knob, South Australia).

Rarity

Very rare

For collectors

## Quality Criteria The most prized englishite specimens are those with well-formed, sharp crystals forming aesthetic, radial aggregates. Contrast with the rock matrix and co-occurrence with other rare phosphates are important, as they enhance the scientific and visual value of the specimen. Due to the small size of the crystals, specimens visible to the naked eye are more desirable. ## Popular Localities Specimens from the classic locality in Clay Canyon, Utah, USA, are by far the most sought after by collectors. They set the standard against which other finds are compared.

Care and storage

## Cleaning Englishite is soft and brittle, so it should be cleaned very carefully. It is best to use a soft brush to remove dust. If necessary, it can be gently rinsed with distilled water, then immediately and thoroughly dried. ## What to Avoid Avoid ultrasonic cleaners, chemical agents, and acids, which can damage the mineral. As a hydrated mineral, it is sensitive to high temperatures, which can cause dehydration and destruction. Protect it from direct sunlight. ## Storage Englishite specimens are best stored in separate, padded boxes to prevent scratches and mechanical damage. Due to its brittleness and small crystal size, it is not a mineral recommended for frequent handling.

Sources

IMA Mineral List (CNMNC)