Brokenhillite
Chemical formula: Mn<sub>8</sub>Si<sub>6</sub>O<sub>15</sub>(OH)<sub>10</sub>
A rare silicate mineral, discovered in the famous Broken Hill deposit in Australia, forming hexagonal, tabular crystals of a reddish-brown color.
Properties
- Mohs hardness
- 4.5
- Luster
- Vitreous, Pearly
- Streak
- Pale brown
- Density
- 3.13
- Cleavage
- Perfect on {0001}
- Fracture
- Micaceous
- Transparency
- Translucent
- Crystal system
- Hexagonal
Diagnostic features
## Identification Identifying brokenhillite under amateur conditions is practically impossible and requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical analysis (EDS/WDS). Preliminary identification is based on its characteristic form (small, hexagonal flakes), reddish-brown color, and co-occurrence with other minerals from Broken Hill. ## Distinguishing from Similar Minerals It can be confused with other rare manganese silicates from the same locality, such as piemontite or bustamite, but differs from them in crystal habit. Piemontite forms prismatic crystals, while bustamite typically forms massive or fibrous aggregates. Definitive differentiation requires specialized studies. ## Crystal Forms Brokenhillite crystallizes in the form of thin, tabular crystals with a hexagonal outline. It often forms radial or rosetted aggregates, and also occurs as single, dispersed flakes within the rock.
Geological environment
## Genesis It is a mineral of metamorphic origin. It forms in zinc, lead, and manganese ore deposits that have undergone high-grade metamorphism. It occurs in manganese-rich rocks, such as rhodochrosite and spessartine. ## Mineral Associations It most commonly co-occurs with galena, sphalerite, quartz, rhodochrosite, spessartine, bustamite, piemontite, and other rare manganese minerals characteristic of the Broken Hill deposit. ## Localities The only confirmed and described occurrence of this mineral in the world is its type locality – the Broken Hill deposit in Yancowinna County, New South Wales, Australia.
Rarity
Very rare
For collectors
## Quality Criteria The most highly valued specimens are those with well-formed, sharp crystals forming aesthetic, rosetted aggregates. Color contrast with the surrounding host rock (matrix) is also important. Due to the microscopic size of the crystals, specimens suitable for viewing under magnification are the most sought after. ## Popular Localities The only source of brokenhillite specimens is the Broken Hill mine in Australia. This mineral is extremely rare, and specimens rarely appear on the market.
Care and storage
## Cleaning Specimens should only be cleaned mechanically, using a soft brush to remove dust. Due to its rarity and potential instability, contact with water and any chemical agents should be avoided. ## What to Avoid Ultrasonic cleaners, chemical agents (acids and bases), and sudden temperature changes should be avoided. The mineral is relatively soft and brittle, therefore requiring careful handling. ## Storage It is recommended to store specimens in stable conditions, in closed collector boxes, to protect them from dust, mechanical damage, and humidity. It is best stored within its original host rock, which provides greater stability.