Mcgillite
Chemical formula: Mn<sup>2+</sup><sub>8</sub>Si<sub>6</sub>O<sub>15</sub>(OH)<sub>8</sub>Cl<sub>2</sub>
McGillite is a rare, pink manganese silicate, forming platy or fibrous aggregates, found in manganese ore deposits.
Properties
- Mohs hardness
- 4
- Luster
- Pearly, Vitreous
- Streak
- Pale pink
- Density
- 3.57
- Cleavage
- Perfect on {001}
- Fracture
- Uneven
- Transparency
- Translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Key diagnostic features of mcgillite include its characteristic pink to purplish-pink color, pearly luster on cleavage surfaces, and occurrence in platy or fibrous aggregates. Excellent cleavage in one direction is also very characteristic. ## Distinguishing from Similar Minerals McGillite can be confused with other pink manganese silicates, such as rhodochrosite or rhodonite. However, it is distinguished by its lower hardness (4) compared to rhodonite (5.5-6.5) and a different mode of occurrence – rhodochrosite more often forms rhombohedral crystals or compact and granular aggregates. The pearly luster on cleavage planes is also a distinguishing feature of mcgillite. ## Crystal Forms Crystals are rare, usually very small, and have a tabular or platy form. It most commonly occurs as scaly, platy, or fibrous aggregates, often forming rosette-like clusters.
Geological environment
## Genesis McGillite is a low-temperature hydrothermal mineral. It forms as a result of metamorphism or metasomatism within manganese-rich sedimentary rocks, such as manganese ore deposits. It forms in veins cutting through these rocks. ## Mineral Associations This mineral co-occurs with other manganese minerals. In its type locality (Sullivan Mine, Canada), it was found in association with pyrochroite, rhodochrosite, weldonite, bementite, tephroite, and alabandite. In Japan, it is accompanied by, among others, rhodochrosite, sonolite, galaxite, and pyroxmangite. ## Localities The most important and well-documented mcgillite localities worldwide include: - Sullivan Mine in Kimberley, British Columbia, Canada (type locality). - Kyurazawa Mine, Tochigi Prefecture, and Taguchi Mine, Aichi Prefecture, Japan.
Rarity
Very rare
For collectors
## Quality Criteria The most prized mcgillite specimens are those that exhibit an intense, pink color and well-formed, rosette-like aggregates of platy crystals. Association with other rare manganese minerals is also important, as it enhances the scientific and aesthetic value of the specimen. Due to its rarity, even small but well-defined specimens are sought after by collectors specializing in mineral systematics or manganese minerals. ## Popular Localities By far the most desirable specimens come from the type locality at the Sullivan Mine in Canada, which is now inactive, making material from this location historical and difficult to acquire. Specimens from Japanese mines are also valued, often exhibiting slightly different mineral associations.
Care and storage
## Cleaning McGillite is a relatively soft and brittle mineral with excellent cleavage. It should be cleaned only mechanically, using a soft brush to remove dust. The use of water is not recommended due to the risk of damaging delicate aggregates. ## What to Avoid Avoid contact with chemicals, especially acids, which can damage it. Due to its low hardness, it is susceptible to scratches. Protect it from impacts and falls. ## Storage McGillite specimens are best stored in separate, padded collector's boxes to prevent abrasion and mechanical damage. It should be protected from dust and moisture.