Embreyite

Chemical formula: Pb<sup>2+</sup><sub>5</sub>(Cr<sup>6+</sup>O<sub>4</sub>)<sub>2</sub>(PO<sub>4</sub>)<sub>2</sub>·H<sub>2</sub>O

Embreyite is a very rare, orange-red secondary mineral, which is a hydrated lead chromate and phosphate.

## Characteristics Embreyite is an extremely rare secondary mineral from the chromate and phosphate group. It forms very small, tabular or prismatic crystals, rarely exceeding 1 mm in length. Most often, it occurs as thin coatings, earthy or powdery aggregates, and microscopic, rosette-like aggregates on host rocks. Its characteristic feature is an intense, orange-red to yellowish-orange color. ## Physical properties Embreyite crystals exhibit an adamantine to resinous luster. The mineral is opaque, only translucent on thin edges. Due to the small size of the crystals, its physical properties, such as hardness, are difficult to measure precisely. It is a very dense mineral due to its high lead content. ## Colors and varieties This mineral occurs in a characteristic range of colors from orange-red, through reddish-orange, to yellowish-orange. No color or commercial varieties are distinguished. ## History and name The name embreyite was given in honor of Peter Godwin Embrey (1929–2012), a British mineralogist and curator at the Natural History Museum in London, in recognition of his contributions to mineralogy. The mineral was first described in 1972 based on samples from the Berezovsk mine in the Urals (Russia) and the Callenberg mine in Saxony (Germany). ## Applications Embreyite has no industrial application. Its significance is purely scientific and collectible due to its extreme rarity and the attractive appearance of microscopic specimens.

Properties

Mohs hardness
3.5
Luster
Adamantine
Streak
Orange-yellow
Density
6.4
Cleavage
Perfect on {100}
Fracture
Uneven
Transparency
Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Embreyite is identified by its characteristic orange-red color, its occurrence as microscopic coatings or small crystals on rocks containing other secondary lead minerals. Its co-occurrence with minerals such as crocoite, wauquelinite, and pyromorphite is also key. ## Distinguishing from similar minerals It can be confused with crocoite, which has a similar color but usually forms larger, better-formed prismatic crystals. Wauquelinite can also be similar, often having a more greenish or olive hue and forming aggregates with different morphology. Final differentiation requires advanced analytical methods, such as X-ray diffraction (XRD) or EDS spectroscopy. ## Crystal forms Embreyite forms very small, tabular crystals with a hexagonal or rhombic outline, often flattened. It also occurs as rosette-like or radial aggregates, as well as earthy and powdery coatings on the rock surface.

Geological environment

## Genesis Embreyite is a secondary mineral, forming in the oxidation (weathering) zones of polymetallic ore deposits rich in lead. Its crystallization occurs as a result of reactions between solutions containing chromate and phosphate ions and primary lead minerals, such as galena. ## Mineral associations This mineral most often co-occurs with other secondary lead minerals. Typical associated minerals include crocoite, wauquelinite, pyromorphite, cerussite, cassedanneite, as well as quartz and goethite. ## Localities The most important and classic localities for embreyite are the Berezovsk mine in the Urals, Russia, and the Callenberg mine in Saxony, Germany. Its occurrence has also been confirmed in Dundas, Tasmania (Australia), the Phoenixville mine in Pennsylvania (USA), and several locations in Scotland (Leadhills-Wanlockhead).

Rarity

Very rare

For collectors

## Quality criteria The most prized embreyite specimens are those that possess visible, even under a microscope, well-formed crystals of intense, orange-red color. Rich crystalline aggregates covering a significant area of the rock matrix are highly valued. Contrast with associated minerals, such as white cerussite or green pyromorphite, also enhances the specimen's attractiveness. ## Popular localities Specimens from the historical localities of the Berezovsk mine (Russia) and Callenberg (Germany) are considered among the best in the world. In recent years, interesting micromounts from Dundas, Tasmania, have also appeared on the market.

Care and storage

## Cleaning Embreyite specimens are extremely delicate and usually microscopic. They should not be cleaned mechanically or chemically. If necessary, compressed air (from a safe distance) can be used to remove dust. Any contact with water or chemicals is inadvisable. ## What to avoid Contact with water, acids, and other cleaning agents should be strictly avoided. The mineral is sensitive to shock and abrasion. Due to its lead and chromium content, avoid inhaling dust and wash hands after any contact with the specimen. ## Storage Specimens should be stored in sealed, stable "micromount" containers, protecting them from dust, moisture, and mechanical damage. They should be kept away from sources of vibration and direct sunlight.

Sources

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