Mendipite
Chemical formula: Pb<sup>2+</sup><sub>3</sub>O<sub>2</sub>Cl<sub>2</sub>
Mendipite is a rare lead oxychloride, valued for its silky luster and characteristic fibrous or radial aggregates.
Properties
- Mohs hardness
- 2.5-3
- Luster
- Pearly
- Streak
- White
- Density
- 7.2-7.24
- Cleavage
- Perfect on {010}
- Fracture
- Conchoidal
- Transparency
- Transparent to translucent
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Fibrous or radial habit, high density (the specimen feels heavy for its size), pearly or silky luster, and perfect cleavage in one direction are key diagnostic features. Darkening under light is also characteristic. ## Distinguishing from Similar Minerals Mendipite is sometimes confused with other secondary lead minerals, such as cerussite or anglesite, which often occur with it. However, cerussite is harder (3-3.5) and often forms reticulated crystal aggregates. Fiedlerite and laurionite, also lead oxychlorides, have different optical and structural properties, and their differentiation requires advanced research methods. ## Crystal Forms It crystallizes in the orthorhombic system. Crystals, though very rare, take on prismatic or columnar forms. It is most commonly found as fibrous, radial aggregates or in compact, massive forms.
Geological environment
## Genesis Mendipite is a secondary mineral formed in the oxidation zones of lead ore deposits, especially in the presence of chloride ions. It forms as a result of the alteration of galena (PbS) in an environment rich in oxygen and chlorides, often originating from saline waters or from interaction with chlorine-bearing minerals, such as apatite. ## Mineral Associations It often co-occurs with other secondary lead minerals, such as cerussite, anglesite, hydrocerussite, as well as other rare lead oxychlorides, e.g., diaboleite, chloroxiphite, paralaurionite, and fiedlerite. Calcite may also accompany it. ## Localities The most important and historical locality is the manganese and lead ore mines in the Mendip Hills, Somerset, England. It is also known from Laurion in Greece; Baratti in Italy; the Kintore mine in Broken Hill, New South Wales, Australia; and from Tiger in Arizona, USA.
Rarity
Very rare
For collectors
## Quality Criteria The most prized specimens by collectors are those with well-formed, visible crystals, which is an enormous rarity. Rich, clean fibrous aggregates with a silky luster, contrasting with the rock matrix, are also highly valued. The size of the specimen and the absence of mechanical damage significantly increase its value. Association with other rare secondary minerals is also important. ## Popular Localities Classic and most desired specimens come from historical localities in England (Mendip Hills) and Laurion in Greece. Specimens from these places have the greatest historical and collectible value.
Care and storage
## Cleaning Mendipite specimens should only be cleaned mechanically, using a very soft brush to remove dust. The use of water, especially ultrasonics, is absolutely not recommended. The mineral is sensitive to chemicals and can be damaged. ## What to Avoid Avoid exposure to sunlight, which causes darkening and surface decomposition of the mineral. It should be protected from moisture, acids, and sudden temperature changes. As a lead mineral, it is toxic – avoid inhaling dust and wash hands after each contact. ## Storage It is recommended to store specimens in closed, dry, and dark containers (e.g., membrane boxes or mineralogical display cases). Due to its softness, it should be isolated from harder minerals to prevent scratching.