Mojaveite
Chemical formula: Cu<sup>2+</sup><sub>6</sub>[Te<sup>6+</sup>O<sub>4</sub>(OH)<sub>2</sub>](OH)<sub>7</sub>Cl
Mojaveite is a very rare secondary mineral of the tellurate group, forming microscopic crystals of an intensely emerald-green color.
Description
## Characteristics Mojaveite is a copper and tellurium mineral that visually presents as coatings and aggregates of small, bladed or tabular crystals. Its most characteristic feature is its vivid, emerald-green, and sometimes blue-green color. Crystals rarely exceed a fraction of a millimeter in length, forming druses covering the rock matrix or filling small fissures. Due to their size, individual crystals are usually only observable under magnification. ## Physical Properties This mineral is characterized by a vitreous luster. It is transparent to translucent. Its Mohs hardness is approximately 3, making it relatively soft and susceptible to scratching. The density calculated from the chemical formula and unit cell parameters is 4.33 g/cm³, but this has not been empirically confirmed due to the small size of the crystals. ## Colors and Varieties The dominant and only known color of mojaveite is an intense emerald-green, which can transition to blue-green tones. No color varieties or commercial varieties are distinguished. ## History and Name The mineral's name, approved in 2013, comes from its discovery location – the Mojave Desert in California, USA. It was first identified in material from the small Bird Nest mining prospect on Otto Mountain in San Bernardino County. It was described by a team of mineralogists led by Anthony R. Kampf. ## Applications Mojaveite has no industrial applications. Its significance is purely scientific and collectible, being a coveted object for advanced collectors specializing in rare minerals or tellurium minerals.
Diagnostic features
## Identification The key diagnostic feature of mojaveite is its characteristic emerald-green color, bladed crystal habit, and occurrence environment. Positive identification is almost exclusively possible based on chemical analysis (e.g., EDS), which will show the presence of copper and tellurium, and by knowing the associated minerals. ## Distinguishing from Similar Minerals Mojaveite can be confused with other green secondary copper minerals, such as brochantite, malachite, or other rare tellurates (e.g., xocomecatlite). It is distinguished from brochantite by its crystal habit (blades instead of needles), and from malachite by the lack of effervescence with hydrochloric acid. Co-occurring xocomecatlite usually forms spherical aggregates (spherulites), not individual, elongated crystals. However, definitive differentiation requires advanced research methods. ## Crystal Forms Mojaveite forms very small, thin, bladed or tabular crystals, elongated in one direction. They often occur as dispersed, radial, or reticulated aggregates on the surface of the host rock.
Geological environment
## Genesis It is a secondary mineral, formed in the oxidation zones (so-called iron caps) of polymetallic, hydrothermal ore deposits that are rich in tellurium. It crystallizes as a result of the weathering of primary copper tellurides and other minerals under desert conditions. ## Mineral Associations Mojaveite often occurs in association with other rare tellurates and tellurites, which is an important clue for identification. Its typical associated minerals include: khinite, parakhinite, dugganite, xocomecatlite, as well as cerussite, chlorargyrite, bromargyrite, and native gold. ## Localities The most important and type locality is Otto Mountain in San Bernardino County, California, USA. It is also known from several mines in the Tombstone area of Cochise County, Arizona (USA), such as the Emerald and Joe mines.
Rarity
Very rare
Collector aspects
## Quality Criteria The collectible value of a specimen is primarily determined by the richness and coverage of the mineral on the surface – the denser and more extensive the druse, the better. The intensity and purity of the emerald color are important. Although the crystals are always small, specimens with well-formed blades visible under magnification are more highly valued. An additional advantage is the association with other rare minerals, especially with well-formed khinite or native gold. ## Popular Localities The most prized specimens by collectors come from the type locality – Otto Mountain in California. Material from mines in the Tombstone area of Arizona also provides high-quality microcrystals.
Care and storage
## Cleaning Mojaveite specimens should be cleaned with the utmost care, using only a soft, dry brush to remove dust. If necessary, a brief rinse in distilled water is permissible, followed by immediate and thorough drying. Ultrasonic cleaners should not be used. ## What to Avoid The mineral is sensitive to acids and ammonia, which can damage or destroy it. Any contact with household and laboratory chemicals should be avoided. Due to its low hardness, it must be protected from abrasion and scratching by harder minerals. ## Storage The safest way to store it is to place the specimen in a sealed "micromount" box, which protects it from dust, mechanical damage, and direct contact. The mineral is stable under household conditions and does not require special humidity or temperature control.