Susannite

Chemical formula: Pb₂+₄(S₆+O₄)(CO₃)₂(OH)₂

A rare lead sulfate and carbonate, a polymorph of leadhillite, forming tabular, pseudohexagonal crystals with strong yellow fluorescence.

## Characteristics Susannite is a rare secondary lead mineral, belonging to the sulfate and carbonate group. It is one of three polymorphs with the same chemical formula – the others being leadhillite and macphersonite. It most often occurs as thin to thick tabular crystals with a distinct, hexagonal outline, which can be arranged in parallel or fan-shaped aggregates. Crystals can be transparent and well-formed, making them attractive to collectors. ## Physical Properties This mineral is relatively soft, with a Mohs hardness of 2.5-3. It is characterized by a very high density, typical for lead minerals, of about 6.5 g/cm³. It has perfect cleavage in one plane, which makes it brittle and prone to delamination. The luster is most often adamantine (diamond-like) or resinous, becoming pearly on cleavage surfaces. One of its most characteristic features is a strong, bright yellow fluorescence under ultraviolet (UV) light. ## Colors and Varieties Susannite is most often colorless or white. It can also take on pale yellow, greenish, gray, and even bluish hues. Specimens showing color zoning, where different parts of the crystal have slightly different coloration, are sometimes found. No commercial names or varieties are distinguished. ## History and Name The mineral's name comes from its discovery locality – the Susanna Mine in Leadhills, Lanarkshire, Scotland. It was described as a distinct mineral in 1820. It is a trigonal polymorph of monoclinic leadhillite, meaning it has the same chemical composition but a different crystal structure. ## Uses Due to its rarity and small accumulations, susannite has no industrial application. It is solely an object of interest for mineral collectors and scientific institutions.

Properties

Mohs hardness: 2.5-3
Luster: Adamantine, Resinous, Pearly
Streak: White
Density: 6.5-6.55
Cleavage: Perfect on {0001}
Fracture: Conchoidal
Transparency: Transparent to translucent
Crystal system: Trigonal

Diagnostic features

## Identification Key diagnostic features of susannite include its tabular, pseudohexagonal crystal habit, very high density (the specimen is surprisingly heavy for its size), perfect cleavage in one direction, and adamantine luster. The most important and often decisive feature, however, is its intense, yellow fluorescence under UV light. ## Distinguishing from Similar Minerals Susannite is most often confused with its polymorph, leadhillite. Distinguishing them without specialized tests (e.g., X-ray diffraction) is extremely difficult, and often impossible. Susannite crystallizes in the trigonal system, and leadhillite in the monoclinic, which can subtly affect crystal symmetry. Strong yellow fluorescence is much more common and intense in susannite. It can also be confused with cerussite, which is harder and does not exhibit cleavage, and with anglesite, which has a different crystal habit. ## Crystal Forms Crystals are in the form of thin or thick tablets with a hexagonal outline. They often form parallel intergrowths, as well as fan-shaped and rosette aggregates. Pyramidal forms are rarer.

Geological environment

## Genesis Susannite is a secondary mineral, forming in the oxidation (weathering) zones of lead ore deposits, mainly galena. It forms as a result of reactions of sulfate- and carbonate-rich solutions with primary lead minerals. It is a low-temperature mineral, although it is considered a high-temperature variety relative to leadhillite. ## Mineral Associations It most often co-occurs with other secondary lead minerals. Its typical associations include leadhillite, cerussite, anglesite, lanarkite, caledonite, and also with primary galena. ## Localities The most important localities worldwide include the historical type locality in Leadhills, Scotland. Beautiful, well-formed crystals come from the famous Tsumeb Mine in Namibia. Other known localities include Broken Hill in Australia, the Tiger Mine in Arizona (USA), and some mines in Cumbria, England.

Rarity

Rare

For collectors

## Quality Criteria Most valued by collectors are specimens with sharp, well-formed, transparent crystals with a distinct hexagonal outline. The size of the crystals and their clarity (lack of inclusions and damage) are highly rated. The attractiveness of a specimen is also enhanced by its aesthetic arrangement on the rock matrix and the presence of other rare secondary minerals. Specimens with distinct coloration (e.g., yellow or green) are usually more sought after than colorless ones. ## Popular Localities Specimens from Scotland (Leadhills), which have historical significance, are considered classic and most desirable. However, the largest and some of the most perfect susannite crystals come from the Tsumeb Mine in Namibia. Specimens from Tsumeb, often with beautiful color and luster, fetch the highest prices on the collector's market.

Care and storage

## Cleaning Special care must be taken due to its softness and perfect cleavage. For removing dust and loose contaminants, a soft brush is best. If necessary, the specimen can be very gently rinsed in distilled water. Absolutely avoid ultrasonic cleaners, which can cause crystals to disintegrate along cleavage planes. ## What to Avoid Susannite, as a carbonate, is sensitive to acids, which cause its rapid dissolution. It should be protected from impacts and scratching by harder minerals. It is brittle, so it requires gentle handling. Sudden temperature changes should be avoided. ## Storage Susannite specimens are best stored in separate, padded boxes to prevent mechanical damage and contact with other minerals. It is advisable to protect it from dust, which can accumulate on crystal surfaces.