Larsenite
Chemical formula: Pb²⁺Zn²⁺SiO₄
Larsenite is a rare lead zinc silicate, valued by collectors for its strong, yellowish-green fluorescence under shortwave UV light.
Properties
- Mohs hardness
- 3
- Color
- Colorless, white
- Luster
- Vitreous to greasy
- Streak
- White
- Density
- 5.90
- Cleavage
- Good on {120}
- Fracture
- Irregular/Uneven
- Transparency
- Transparent
- Crystal system
- Orthorhombic
Diagnostic features
## Identification The most important diagnostic feature of larsenite is its very strong, lemon-yellow to yellowish-green fluorescence under shortwave UV light. In daylight, it is an inconspicuous, whitish or colorless mineral with a greasy luster, occurring in massive aggregates. High density is also a helpful indicator. ## Distinguishing from Similar Minerals Larsenite is sometimes confused with other white or colorless minerals from the Franklin deposit, such as willemite or calcite. Willemite also exhibits fluorescence (usually green), but it is much harder (5.5 on the Mohs scale). Calcite is much lighter, more common, reacts with hydrochloric acid, and its fluorescence (if present) is usually red or orange. Clinohedrite, another rare mineral from Franklin, fluoresces orange. ## Crystal Forms Larsenite forms poorly developed, prismatic crystals, often with a nearly square cross-section. However, it is most commonly found in granular aggregates, massive forms, or as fillings in small rock fractures.
Geological environment
## Genesis Larsenite is a mineral of metamorphic origin. It formed as a result of contact metamorphism of zinc, lead, and manganese ore deposits, embedded in Precambrian carbonate rocks (marbles). It is a product of late hydrothermal processes occurring within the deposit. ## Mineral Associations This mineral co-occurs with many other rare minerals from the Franklin deposit. It is most commonly associated with: willemite, franklinite, zincite, andradite, calcite, clinohedrite, rhodochrosite, and barite. ## Localities The only confirmed and classic locality for larsenite in the world is the Franklin Mine in Franklin, Sussex County, New Jersey, USA. This is the type locality for this mineral.
Rarity
Very rare
For collectors
## Quality Criteria Specimens of larsenite exhibiting the strongest and purest yellow fluorescence are most valued by collectors. Its attractiveness is enhanced by rich associations with other fluorescent minerals from Franklin, such as calcite (red fluorescence) and willemite (green fluorescence), creating multicolored compositions under UV light. The size of the specimen and the abundance of larsenite in the matrix are also important. ## Popular Localities Since larsenite occurs exclusively in the Franklin Mine in New Jersey, all collector specimens originate from this single, historic locality. The mine is now closed and converted into a museum, meaning new specimens are no longer being acquired, and material on the market comes solely from old collections.
Care and storage
## Cleaning Larsenite specimens should be cleaned very carefully, using a soft brush to remove dust. Due to its softness and brittleness, ultrasonic cleaners and hard brushes should be avoided. If water is necessary, it should be distilled water, and the specimen should be thoroughly dried immediately. ## What to Avoid Avoid contact with acids and other chemicals that can damage the mineral's surface. Larsenite is sensitive to impact and scratches. It should not be heated or exposed to rapid temperature changes. ## Storage Larsenite specimens should be stored separately in padded boxes to avoid contact with harder minerals. It is best to keep them in stable conditions, away from moisture and direct sunlight, although sunlight does not significantly affect it.