Nantokite
Chemical formula: Cu¹⁺Cl
Nantokite is a rare copper(I) chloride that is colorless and crystallizes in the isometric system, but quickly oxidizes and turns green in air.
Properties
- Mohs hardness
- 2-2.5
- Color
- Colourless, white to greyish, greenish
- Luster
- Adamantine
- Streak
- White
- Density
- 3.93
- Cleavage
- On {011}.
- Fracture
- Conchoidal
- Transparency
- Transparent
- Crystal system
- Isometric
Diagnostic features
## Identification Fresh, colorless nantokite can be identified by its adamantine luster and high density. A key diagnostic feature is its rapid reaction to humid air – it becomes covered with a green coating within minutes or hours. This is a destructive but unambiguous test. The mineral is also sectile and can be cut with a knife. ## Distinguishing from Similar Minerals Colorless nantokite can be confused with halite or sylvite, from which it is distinguished by its significantly higher density and immediate reaction to moisture. It can also be confused with cerussite, which has a similar luster and density, but is much harder and does not react to air in this way. ## Crystal Forms Nantokite crystallizes in the isometric system, forming rare, poorly developed tetrahedral crystals. Most often, it occurs as massive, granular, or compact aggregates, as well as veins and fillings in the host rock.
Geological environment
## Genesis Nantokite is a secondary mineral, forming in the oxidation zones of copper deposits, but under specific, strongly reducing and dry (anhydrous) conditions. It forms as a result of the reaction of chlorine-rich solutions with primary copper sulfides in a desert climate. It can also form as a product of volcanic exhalations (sublimate). ## Mineral Associations It co-occurs with other minerals of the oxidation zone, such as atacamite, paratacamite, cuprite, native copper, as well as halite and sylvite. ## Localities The most important nantokite localities worldwide include the Atacama Desert in Chile (Nantoko, Chuquicamata, El Cobre mines), Broken Hill in Australia, the Bischofite mine in Tasmania, and some localities in Arizona (USA). It also occurs as a product of modern volcanic exhalations at Vesuvius in Italy.
Rarity
Very rare
For collectors
## Quality Criteria For collectors, the purity and transparency of the specimen are paramount. Colorless, transparent fragments, even small ones, that have been properly protected from oxidation (e.g., in oil or special inert gas containers) are most valued. Specimens with well-formed, though rare, crystals are extremely valuable. The presence of a green coating of decomposition products significantly reduces collector value. ## Popular Localities The most classic and prized specimens come from historical finds in Broken Hill, Australia, and the Atacama Desert in Chile. Specimens from these localities are considered exemplary for this mineral.
Care and storage
## Cleaning Cleaning nantokite is highly inadvisable and practically impossible without specialized equipment. Any contact with water, alcohol, or other liquids will cause its immediate and irreversible oxidation. Specimens should be left in the state in which they were acquired. ## What to Avoid Contact with moisture and air must be strictly avoided. Even brief exposure to standard atmospheric humidity (above 30%) initiates the decomposition process. The mineral is very soft and brittle, so all types of impacts and scratches should be avoided. ## Storage The only effective methods for storing nantokite are to keep it in a complete vacuum, in an atmosphere of dry inert gas (e.g., argon), or immersed in an anhydrous, chemically inactive liquid such as paraffin oil or toluene. Display in standard collector boxes, even seemingly sealed ones, leads to its destruction.