Johninnesite
Chemical formula: Na<sub>2</sub>Mn<sup>2+</sup><sub>9</sub>Mg<sub>7</sub>(As<sup>5+</sup>O<sub>4</sub>)<sub>2</sub>(Si<sub>6</sub>O<sub>17</sub>)<sub>2</sub>(OH)<sub>8</sub>
Johninnesite is a very rare, complex sodium, manganese, and magnesium silicate and arsenate, forming brown, tabular crystals.
Properties
- Mohs hardness
- 4
- Luster
- Vitreous
- Streak
- Pale brown
- Density
- 3.45
- Cleavage
- Perfect on {010}
- Fracture
- Uneven
- Transparency
- Translucent
- Crystal system
- Triclinic
Diagnostic features
## Identification Johninnesite can be identified by its characteristic brown color, tabular crystal habit, radial aggregates, and occurrence in a specific geological environment. Perfect cleavage in one direction is also a helpful feature. ## Distinguishing from Similar Minerals It can be confused with other rare manganese silicates from Broken Hill, such as piemontite or other minerals from the pyroxmangite group. Final differentiation requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical analysis (EDS/WDS), due to its co-occurrence with many visually similar minerals. ## Crystal Forms It forms flattened, tabular or bladed crystals, which often arrange themselves into fan-shaped or radial aggregates. Crystals are small, rarely exceeding a few millimeters in length.
Geological environment
## Genesis Johninnesite is a metamorphic mineral. It forms in zinc, lead, and manganese ore deposits that have undergone high-grade metamorphism. It occurs in rocks rich in manganese and silicon, in association with other rare minerals. ## Mineral Associations This mineral co-occurs with minerals such as galena, sphalerite, bustamite, rhodochrosite, quartz, calcite, as well as other rare manganese arsenates and silicates typical of the Broken Hill deposit. ## Localities The only confirmed locality (type locality) of johninnesite in the world is the Broken Hill deposit in New South Wales, Australia.
Rarity
Extremely rare
For collectors
## Quality Criteria The most valued specimens are those with well-formed, sharp crystals forming aesthetic, radial aggregates. Contrast with the rock matrix and the presence of rare associated minerals are also important. Due to its rarity, any well-identified specimen has high value for collectors specializing in systematics or minerals from the Broken Hill deposit. ## Popular Localities The only source of specimens is the historic Broken Hill deposit in Australia. This mineral is found extremely rarely, and new specimens practically do not enter the market. Most material is held in institutional collections and old, specialized private collections.
Care and storage
## Cleaning Specimens should be cleaned only very carefully, using a soft brush to remove dust. Due to the presence of arsenic, inhaling dust should be avoided. Washing hands after contact with the mineral is recommended. ## What to Avoid Avoid contact with water and chemicals, especially acids, which can damage the mineral. It is relatively soft and brittle, so it must be protected from impacts and scratches. It should not be heated or subjected to ultrasound. ## Storage Store in stable conditions, away from moisture and dust, preferably in a closed display box. It should be kept separate from harder minerals to prevent scratching.