Joesmithite
Chemical formula: Pb<sup>2+</sup>Ca<sub>2</sub>Mg<sub>3</sub>Fe<sup>3+</sup><sub>2</sub>(Si<sub>6</sub>Be<sub>2</sub>)O<sub>22</sub>(OH)<sub>2</sub>
Joesmithite is a very rare amphibole group mineral, distinguished by its reddish-brown color and occurrence almost exclusively in Långban, Sweden.
Description
## Characteristics Joesmithite is a complex silicate belonging to the amphibole supergroup. It typically forms subhedral, prismatic crystals or irregular grains embedded in the host rock. Its most characteristic visual feature is a deep, reddish-brown to almost black color. Well-formed, freestanding crystals are rarely encountered. ## Physical Properties This mineral is characterized by a hardness of approximately 5.5 on the Mohs scale and a vitreous luster. It is translucent to almost opaque. Its density is relatively high at 3.77 g/cm³, which is a result of the presence of lead in its chemical structure. ## Colors and Varieties The dominant and virtually only color found in joesmithite is a shade from reddish-brown to brownish-black. No color or commercial varieties are distinguished. ## History and Name Joesmithite was first described in 1968. Its name honors Joseph V. Smith (1928–2007), a distinguished mineralogist and crystallographer from the University of Chicago, for his contributions to silicate research. The discovery site and type locality is the famous Långban deposit in Sweden. ## Uses Due to its extreme rarity, joesmithite has no industrial applications. It is solely an object of scientific interest and a prized acquisition for advanced systematic and regional mineral collections.
Diagnostic features
## Identification Key features for identifying joesmithite are its characteristic reddish-brown color, vitreous luster, relatively high density, and prismatic form typical of amphiboles. However, the most important indicator is its origin from the Långban or Jakobsberg mine in Sweden. ## Distinguishing from Similar Minerals It can be confused with other dark minerals from Långban, such as some varieties of richterite, aegirine, or piemontite. Definitive differentiation from similar amphiboles and pyroxenes often requires advanced analytical methods, such as X-ray microanalysis (EDS), to confirm its unique chemical composition with the presence of lead and beryllium. ## Crystal Forms Joesmithite most often occurs as embedded, prismatic crystals with imperfect development or as granular aggregates. Well-terminated, single crystals are exceptionally rare and highly sought after.
Geological environment
## Genesis This is a mineral of metamorphic origin. It forms in complex, metamorphosed iron and manganese ore deposits, deposited in carbonate rocks (skarns). This environment, rich in unusual elements, favored the crystallization of rare mineral phases. ## Mineral Associations Joesmithite co-occurs with other minerals characteristic of the Långban deposit, such as richterite, phlogopite, calcite, hematite, and other rare manganese and lead minerals. ## Localities The most important and historically first occurrence of joesmithite is the Långban mine in the Värmland region of Sweden. It has also been identified in the nearby Jakobsberg mine. These are practically the only confirmed localities in the world from which specimens of this mineral originate.
Rarity
Very rare
Collector aspects
## Quality Criteria The most highly prized joesmithite specimens are those that contain distinctly formed, even if partially, crystals of intense, reddish-brown color. The contrast with the light host rock (matrix), most often calcite, is of great importance. Crystal size is a key factor influencing value – any crystal above a few millimeters is already considered significant. ## Popular Localities The only source of collector specimens is the historic mining district of Långban in Sweden. Specimens from this locality are classics and adorn any advanced mineral collection.
Care and storage
## Cleaning Joesmithite specimens should be cleaned very carefully, using a soft brush to remove dust. If necessary, distilled water can be used. Ultrasonic cleaners should be absolutely avoided, as they can cause cracks in the crystal. ## What to Avoid This mineral is sensitive to strong acids. It should be protected from impacts and sudden temperature changes. As a rare and valuable specimen, it requires particular caution when handling. ## Storage It is recommended to store specimens in separate, padded boxes to avoid scratches and mechanical damage. They should be displayed away from high-traffic areas, in stable room conditions.