Roquesite
Chemical formula: Cu¹⁺In³⁺S²⁻₂
Roquesite is a rare copper-indium sulfide, characterized by its metallic luster and occurrence in tin deposits.
Properties
- Mohs hardness
- 3.5-4
- Color
- Grey
- Luster
- Metallic
- Streak
- Black
- Density
- 0
- Cleavage
- None
- Fracture
- Uneven
- Transparency
- Opaque
- Crystal system
- Tetragonal
Diagnostic features
## Identification Identifying roquesite is extremely difficult and practically impossible without advanced laboratory methods, such as chemical analysis (EDS) or X-ray diffraction (XRD). Preliminary visual identification relies on finding minute, steel-gray grains with a metallic luster within copper sulfides (bornite, chalcopyrite) in a specific geological environment. ## Distinguishing from Similar Minerals Roquesite is visually almost identical to many other sulfides, such as chalcopyrite, bornite, sphalerite, or tetrahedrite. Distinguishing it from these minerals based on physical characteristics (color, hardness) is unreliable. Certainty is only provided by chemical composition analysis, which will show the presence of indium as a key component. ## Crystal Forms It most often occurs as anhedral (undeveloped) grains ranging in size from microscopic to about 0.5 mm. Very rarely, it forms minute, poorly developed crystals with a tetragonal tetrahedral habit.
Geological environment
## Genesis Roquesite is a mineral of hydrothermal origin. It forms in quartz-tourmaline veins associated with tin (cassiterite) deposits. It crystallizes under medium to high-temperature conditions from solutions rich in copper, indium, and sulfur. ## Mineral Associations This mineral most commonly co-occurs with bornite, chalcopyrite, cassiterite, sphalerite, wolframite, arsenopyrite, and quartz. It often forms microscopic inclusions within them. ## Localities The most important and confirmed roquesite localities worldwide include: - Charrier mine in Allier (Auvergne, France) - type locality. - Mount Pleasant deposit in New Brunswick (Canada). - Toyoha mine in Hokkaido Prefecture (Japan). - Tin deposits in the Potosí region (Bolivia). - Yaogangxian mine in Hunan Province (China).
Rarity
Very rare
For collectors
## Quality Criteria The quality of a roquesite specimen is determined almost exclusively by its visibility and identifiability. Specimens in which roquesite grains are large enough (above 0.1-0.2 mm) to be observed under a stereomicroscope are most highly valued. Exceptionally rare, well-formed microcrystals achieve the highest value. The presence on a matrix with well-defined associated minerals also enhances the specimen's appeal. ## Popular Localities Specimens from the type locality (Charrier mine in France) have particular historical value. However, most micromineral specimens available on the collector's market come from the Mount Pleasant deposit in Canada and the Toyoha mine in Japan, which have provided the best-studied samples.
Care and storage
## Cleaning Roquesite specimens, due to their microscopic size and occurrence as inclusions, practically do not require cleaning. If necessary, only compressed air should be used to remove dust. Contact with water and any chemicals should be avoided. ## What to Avoid Contact with acids and other chemical agents that can destroy the mineral must be strictly avoided. As a sulfide, it is susceptible to oxidation, so it should be protected from moisture and sudden temperature changes. ## Storage Specimens containing roquesite are best stored under stable conditions, in sealed, dry containers (e.g., "micromount" type), to minimize the risk of oxidation and protect against dust. Due to its softness, contact with harder minerals should be avoided.